D9310.PDF

Rev. sci. tech. Off. int. Epiz., 2000,19 (2), 443-462
Newcastle disease and other avian
paramyxoviruses
D.J. Alexander
Central Veterinary Laboratory, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, United Kingdom
Summary
N e w c a s t l e disease (ND), caused by avian paramyxovirus serotype 1 (APMV-1)
viruses, is included in List A of the Office International des Epizooties. Historically,
ND has been a devastating disease of poultry, and in many countries t h e disease
remains one of t h e major problems affecting existing or developing poultry
industries. Even in countries w h e r e ND m a y be considered t o be controlled, an
economic burden is still associated w i t h v a c c i n a t i o n and/or maintaining strict
biosecurity measures. The variable nature of N e w c a s t l e disease virus strains in
t e r m s of virulence f o r poultry and t h e different susceptibilities of t h e different
species of birds mean t h a t f o r control and trade purposes, ND requires careful
definition. Confirmatory diagnosis of ND requires t h e isolation and
characterisation of the virus involved. A s s e s s m e n t s of virulence conventionally
require in vivo testing. However, in vitro genetic characterisation of viruses is
being used increasingly n o w t h a t the molecular basis of pathogenicity is more
fully understood. Control of ND is by prevention of introduction and s p r e a d , good
biosecurity practices and/or v a c c i n a t i o n . N e w c a s t l e disease viruses may infect
humans, usually causing t r a n s i e n t conjunctivitis, but h u m a n - t o - h u m a n spread has
never been reported.
Eight other serotypes of avian paramyxoviruses are r e c o g n i s e d , namely: A P M V - 2
to A P M V - 9 . M o s t of these serotypes appear t o be present in natural reservoirs of
specific feral avian species, although other host species are usually susceptible.
Only A P M V - 2 and A P M V - 3 viruses have made a significant disease and e c o n o m i c
i m p a c t on poultry production. Both types of viruses cause respiratory disease and
egg production losses w h i c h m a y be severe w h e n e x a c e r b a t e d by other
infections or environmental stresses. No reports exist of natural infections of
chickens w i t h A P M V - 3 viruses.
Keywords
Aetiology - Avian diseases - Avian paramyxoviruses Epidemiology - Newcastle disease - Public health.
Control -
Diagnosis
-
Introduction
represents a major limiting factor for increasing poultry
production in many countries.
Two poultry diseases are considered to be sufficiently serious
to be included in List A of the Office International des
Epizooties (OIE), namely: highly pathogenic avian influenza
(HPAI) and Newcastle disease (ND) (85). While HPAI occurs
relatively rarely, ND is enzootic in some areas of the world and
a constant threat to most birds reared domestically. Very few
commercial poultry flocks are not influenced in some way by
measures aimed at controlling ND and spread of the virus (4).
A large majority of the countries rearing poultry commercially
rely on vaccination to control ND, but ND nevertheless
The greatest impact of ND may be on village or backyard
chicken production. In developing countries throughout Asia,
Africa, Central America and some parts of South America, the
village chicken is an extremely important asset representing a
significant source of protein in the form of eggs and meat.
However, ND is frequently responsible for devastating losses
in village poultry. For example, Spradbrow estimated that
9 0 % of the village chickens in Nepal die each year as a result
of ND (107). Social and financial restraints mean that the
Rev. sci. tech. Off. int. Epiz., 19
444
control of ND in village chickens in developing countries is
extremely difficult, if not impossible, and this situation
impinges on the further development of commercial poultry
production and the establishment of trade links.
- mesogenic: viruses causing clinical signs consisting of
respiratory and neurological signs, with low mortality
- lentogenic:
viruses
causing
mild
infections
of
the
respiratory tract
- asymptomatic enteric: viruses causing avirulent infections
Aetiology
in which replication appears to occur primarily in the gut.
Viruses
Although these categories are useful for descriptive purposes,
The three virus families Rhabdoviridae,
Filoviridae
and
Paramyxoviridae
form the order Mononegavirales, i.e. viruses
with negative sense, single-stranded, non-segmented,
ribonucleic acid genomes. Newcastle disease is caused by
avian paramyxovirus serotype 1 (APMV-1) viruses, which
together with viruses of the other eight APMV serotypes
(APMV-2 to APMV-9), have been placed in the genus
Rubulavirus,
sub-family
Paramyxovirinae,
family
Paramyxoviridae,
in the current taxonomy ( 9 5 ) . Recent
studies involving the sequencing of the whole ND virus
(NDV) genome have suggested that avian paramyxoviruses
are sufficiently different from other rubulaviruses to warrant
the creation of a separate genus (45).
The prototype strains of each of the nine serotypes of avian
paramyxoviruses are shown in Table I.
Strains of NDV have been distinguished on the basis of the
clinical signs produced in infected chickens. Beard and
Hanson (29) defined the following five groups or pathotypes:
- viscerotropic velogenic: viruses responsible for disease
characterised by acute lethal infections, usually with
haemorrhagic lesions in the intestines of dead birds
- neurotropic
velogenic:
viruses
causing
disease
characterised by high mortality which follows respiratory and
neurological disease, but in which gut lesions are usually
absent
some overlapping does occur and some viruses are difficult to
place.
Antigenic relationships
Cross relationships in haemagglutination inhibition (HI) and
other tests have been detected between some of the APMV
serotypes ( 7 , 8 ) . However, use of a variety of serological and
non-serological tests has tended to confirm the distinctiveness
of the APMV serotypes. Antigenic relationships between
APMV-1 and other serotypes are important as these may affect
diagnosis of ND. Generally, such cross-reactions in serological
tests are low, but APMV-3 viruses may show sufficiently high
levels of cross reactivity with conventional APMV-1 antisera to
cause problems. Apparent antibodies to APMV-3 virus
detected in chickens have been attributed to high antibody
levels to NDV as a result of vaccination (33).
Antigenic variation between viruses within APMV serotypes
has been reported for most of the serotypes where more than a
few isolates have been obtained. For NDV (APMV-1),
differences detectable by conventional HI tests have been
reported, although only rarely ( 1 2 , 2 6 , 5 4 ) . One of the most
noted variations of this kind has been the virus responsible for
the panzootics in racing pigeons that occurred during the
1980s. The NDV responsible, referred to as pigeon APMV-1
(PPMV-1), was demonstrably different from standard strains
in HI tests, although not sufficiently different that
Table I
Serotypes of avian paramyxovirus
Prototype virus strain
Usual natural hosts
APMV-1 (Newcastle disease virus)
Numerous
APMV-2/chicken/California/Yucaipa/56
Turkeys, passerines
APMV-37turkey/Wisconsin/68
Turkeys
APMV-3*/parakeet/Netherlands/449/75
APMV-4/duck/Hong Kong/D3/75
APMV-5/budgerigar/Japan/Kunitachi/74
APMV-6/duck/Hong Kong/199/77
Psittacines, passerines
Ducks
Budgerigars
Ducks
None
Geese
APMV-7/dove/Tennessee/4/75
APMV-8/goose/Delaware/1053/76
APMV-9/domestic duck/New York/22/78
Pigeons, doves
Ducks, geese
Ducks
Turkeys, ostriches
* Serological tests may distinguish between turkey and psittacine isolates
APMV: avian paramyxovirus
Other hosts
Chickens, psittacines,
rails
None
Lorikeets
Geese, rails, turkeys
Disease produced in poultry
Varies from extremely pathogenic to inapparent, depending on
strain and host infected
Mild respiratory disease or egg production problems: severe if
exacerbation occurs
Mild respiratory disease but severe egg production problems
worsened by exacerbating organisms or environment
No infections of poultry reported
None known
No infections of poultry reported
Mild respiratory disease and slightly elevated mortality in turkeys:
no disease in ducks or geese
Mild respiratory disease in turkeys
No infections of poultry reported
None known
Rev. sci. tech. Off. int. Epiz., 19 (2)
conventional
ND
445
vaccines were
not
protective ( 1 6 ) .
Monoclonal antibodies (mAbs) raised against various strains
of NDV have been used to establish the uniqueness of the
variant NDV responsible for the panzootic of ND in pigeons
Disease
Newcastle disease
and have proven particularly useful in identifying the spread
The clinical signs seen in birds infected with NDV vary widely
of this virus around the world ( 1 4 , 17, 9 1 ) . Monoclonal
and are dependent on factors such as the virus, host species,
antibodies to NDV have also been used to distinguish between
age of host, infection with other organisms, environmental
specific viruses. For example, two groups have described
stress and immune status. In some circumstances, infection
mAbs that distinguish between the common vaccine strains,
with the extremely virulent viruses may result in sudden, high
Hitchner B l and La Sota ( 4 7 , 7 7 ) , while other mAbs can
mortality with comparatively few clinical signs. Although the
separate vaccine viruses from epizootic virus in a given area
clinical signs are variable and influenced by other factors, so
(108).
that none can be regarded as pathognomonic, certain signs do
appear to be associated with particular viruses. This has
Antigenic variation detected by mAb typing has also been
used in epidemiological studies. In a large study of over 1,500
viruses, Alexander et al. (21) used the ability of viruses to react
with panels of mAbs, consisting initially of nine mAbs and
later extended to twenty-six or twenty-eight mAbs, to place
strains and isolates of NDV into groups on the basis of ability
to react with the different mAbs. Viruses in the same mAb
group shared biological and epizootiological properties. Use
resulted in the grouping of viruses into five 'pathotypes' on the
basis of the predominant signs in affected chickens (see
above). These groupings are b y no means clear-cut, and even
in experimental infections of specific-pathogen-free (SPF)
chickens considerable overlapping occurs (9). In addition, in
the field, exacerbating factors may result in the clinical signs
induced by the milder strains mimicking those of the more
pathogenic viruses.
of such panels, particularly the extended panel, has indicated
that viruses tend to remain fairly well conserved during
In general terms, ND may consist of signs of depression,
outbreaks or epizootics and
this often allows valuable
diarrhoea, prostration, oedema of the head and wattles,
assumptions to be made concerning the source and the spread
nervous signs, such as paralysis and torticollis, and respiratory
of ND.
signs ( 7 5 ) . Decline in egg production, perhaps leading to
Variations within other serotypes have been reviewed by
signs of disease and deaths in egg-laying birds. Virulent ND
Alexander (7). Marked variations have been recorded between
strains may replicate in vaccinated birds, but the clinical signs
viruses placed in APMV-2, APMV-3 and APMV-7 serotypes.
will be greatly diminished in relationship to the antibody level
The variations recorded often showed two viruses with little
achieved (24).
complete cessation of egg laying, may precede more overt
relationship to each other, but each showing strong similarity
with a third virus. Ozdemir et al. produced mAbs against
As with clinical signs, no gross or microscopic lesions can be
APMV-2 virus and were able to class isolates from a wide
considered pathognomonic
for any form of ND ( 7 5 ) .
range of hosts and geographical locations into four groups
Carcasses of birds dying as a result of virulent ND usually
(88). The antigenic variations in the APMV-3 group seem to
have a fevered, dehydrated appearance. Gross lesions vary
have greater significance, as these appear to separate turkey
according to the infecting virus. Virulent panzootic NDVs
isolates from psittacine isolates. Anderson et al. produced
typically cause haemorrhagic lesions of the intestinal tract.
mAbs to APMV-3 virus and the use of these suggested that
These are most easily seen if the intestine is opened and may
antigenic variation within the APMV-3 serogroup may be
vary considerably in size. Some authors have reported lesions
more complicated than suggested using polyclonal antisera
most typically in the proventriculus, while others consider
(25).
lesions to be most prominent in the duodenum, jejunum and
ileum. Even in birds showing neurological signs prior to
Phylogenetic studies
death, little evidence is found of gross lesions in the central
Development
nervous system. Lesions are usually present in the respiratory
of
improved
techniques
for
nucleotide
sequencing, the availability of sequence data of NDV placed in
tract
computer
generally appear as haemorrhagic lesions and congestion;
databases
and
the
demonstration
that
even
when
clinical
signs
indicate
involvement.
These
relatively short sequence lengths could give meaningful
airsacculitis may be evident. Egg peritonitis is often seen in
results in phylogenetic analyses has led to a considerable
laying hens infected with virulent NDV.
increase in such studies in recent years. Considerable genetic
diversity has been detected, but viruses sharing temporal,
Microscopic lesions are not considered to have any diagnostic
geographical, antigenic or epidemiological parameters tend to
significance. In most tissues and organs, changes consist of
fall into specific lineages or clades and this has proven
hyperaemia,
necrosis, cellular infiltration
valuable in assessing both the global epidemiology and local
Changes in
the
spread of ND ( 2 3 , 4 0 , 5 7 , 6 7 , 6 8 , 73, 1 0 2 , 1 0 9 ) .
nonpurulent encephalomyelitis.
central nervous
and
oedema.
system are
those of
446
Other avian paramyxoviruses
As summarised in Table I, of the other APMVs, only APMV-2
and APMV-3 viruses have been consistently shown to
infect and cause disease in poultry, although APMV-6 and
APMV-7 viruses have been associated with clinical disease in
turkeys.
Uncomplicated infections of chickens or turkeys with
APMV-2 viruses probably result in only mild respiratory
disease. However, much more serious disease may ensue due
to exacerbation by other organisms. Avian paramyxovirus
serotype 2 viruses have been associated with respiratory and
egg production problems in chickens and turkeys ranging
from mild to severe with elevated mortality. Associated
disease has usually been more severe in turkeys than chickens
(7). Virus isolation and/or the presence of antibodies have also
confirmed APMV-2 virus infections in chicken and turkey
flocks that have experienced no clinical disease (34). The
clinical outcome of infections of domestic poultry with
APMV-2 viruses is probably dependent on exacerbation by
other organisms or environmental conditions. Experimental
infections of laying turkeys showed that egg production and
hatchability were adversely affected although fertility was not
(28).
Avian paramyxovirus serotype 3 viruses have been associated
with respiratory disease and egg production problems in
turkeys (27). To date, no natural infections have been
recorded in chickens, although experimental infections have
demonstrated that these birds are susceptible to the serotype.
In uncomplicated infections of turkeys, the first sign is often a
decline in egg production. However, early mild respiratory
signs have been reported, which suggest the respiratory tract
may be the initial site of infection (10). The decline in egg
production varies considerably according to the age of the
birds and the presence of secondary infections. In
uncomplicated infections of birds a few weeks after beginning
to produce eggs, the effective loss may be around 1-2 eggs per
bird per week for five or six weeks, after which the production
returns to expected levels (32). Production problems are
associated with a high level of white-shelled eggs, and the
hatchability and fertility of eggs are also reduced. Infection at,
or just before, the point of lay may result in more serious
losses, with the flock failing to reach target production
throughout the laying period. Far more serious respiratory
disease and egg production problems have been recorded
when dual infection with NDV (including live vaccines),
influenza viruses, chlamydiae, mycoplasmas or other bacteria
has occurred. No studies have reported on the lesions
associated with APMV-3 infections of turkeys.
Avian paramyxovirus serotype 6 has been isolated on one
occasion from turkeys with egg production and mild
respiratory problems.
Rev. sci. teck Off. int. Epiz., 19
Saif et al. reported APMV-7 virus as the primary pathogen in
natural outbreaks of respiratory disease with elevated
mortality in turkeys. Furthermore, mild respiratory disease
was demonstrated in turkeys infected experimentally (100).
Molecular basis of pathogenicity of Newcastle
disease virus
During replication, NDV particles are produced with a
precursor fusion glycoprotein, F 0 , which has to be cleaved to
F l and F2 for the virus particles to be infectious ( 9 8 ) . This
post translation cleavage is mediated by host cell proteases
(79). Trypsin is capable of cleaving F 0 for all NDV strains and
in vitro treatment of non-infectious virus will induce
infectivity (80).
The importance of F 0 cleavage can be demonstrated by the
ability of viruses normally unable to replicate or produce
plaques in cell culture systems to do both if trypsin is added to
the agar overlay or culture fluid. The cleavability of the FO
molecule was shown to be related directly to the virulence of
viruses in vivo. Viruses pathogenic for chickens could
replicate in a wide range of cell types in vitro with or without
added trypsin, whereas strains of low virulence could
replicate only when trypsin was added (96, 9 7 ) . The FO
molecules of viruses virulent for chickens can apparently be
cleaved by a host protease or proteases found in a wide range
of cells and tissues. This allows these viruses to spread
throughout the host, damaging vital organs. In contrast, FO
molecules in viruses of low virulence appear to have restricted
sensitivity to host proteases, resulting in restriction of these
viruses to growth only in certain host cell types.
Collins et al. compared the deduced amino acid sequences at
the cleavage site of the FO precursor of twenty-six APMV-1
isolates (38). All fourteen viruses that were virulent for
chickens had the sequence
R/K-R-Q-K/R-R
at the
C-terminus of the F2 protein and F (phenylalanine) at residue
117, the N-terminus of the F l protein. The eleven viruses of
low virulence had sequences in the same region of
G/E-K/R-Q-G/E-R
and L (leucine) at residue 117. Thus,
a double pair of basic amino acids was apparently required at
residues 112 and 113, and 115 and 116, plus a phenylalanine
at residue 117, if the virus was to show virulence for chickens.
The exception was the single pigeon variant virus examined
(PPMV-1) which had the sequence G - R - Q - K - R - F ; in
tests in vivo, this virus fell within the definition of viruses
virulent for chickens (see below). Jestin and Cherbonnel
demonstrated a similar motif at the F2/F1 cleavage site for two
viruses isolated from chickens (61), which they grouped
antigenically with PPMV-1 viruses (60). Further studies have
indicated that this variation is usual for PPMV-1 viruses, but
has no significance in the variability of pathogenicity for
chickens recorded with these viruses (39).
112
112
116
116
m
1 1 7
The major influence on the pathogenicity of NDV is therefore
the amino acid motif at the F 0 cleavage site, the presence of
447
Rev. sci. tech. Off. int. Epiz., 19 (2)
basic amino acids at positions 1 1 3 , 115 and 116 and
phenylalanine at 117 in virulent strains means that cleavage
can be effected by protease or proteases present in a wide
range of host tissues and organs. For viruses of low virulence,
cleavage can occur only in the presence of proteases
recognising a single arginine, i.e. trypsin-like enzymes. The
replication of such viruses is therefore restricted to areas
where trypsin-like enzymes are present, such as the
respiratory and intestinal tracts, whereas virulent viruses can
replicate in a range of tissues and organs, resulting in a fatal
systemic infection (96).
Epidemiology
Host range
The natural and occasional hosts of the different APMV
serotypes are summarised in Table I.
Host range of N e w c a s t l e disease
Newcastle disease viruses have been reported to infect animals
other than birds, ranging from reptiles to humans (71). Kaleta
and Baldauf concluded that NDV infections have been
established in at least 2 4 1 species of birds representing 2 7 of
the 5 0 orders of the class ( 6 4 ) . All birds are probably
susceptible to infection, but, as stressed by Kaleta and Baldauf,
the disease observed with any given virus may vary
enormously from one species to another.
Wild
birds
Newcastle disease virus isolates have been obtained frequently
from migratory feral waterfowl and other aquatic birds. Most
of these isolates have been of low virulence for chickens and
similar to viruses of the 'asymptomatic enteric' pathotype. The
potential of such viruses to become virulent and the role of
feral birds in the spread of ND are described below. The most
significant outbreaks of ND in feral birds were those reported
in double-crested cormorants (Phalacrocorax
auritus) in
North America during the 1990s. Newcastle disease in
cormorants and related species had been reported earlier, in
the late 1940s in Scotland (31) and in Quebec in 1975 ( 3 7 ) .
Recent outbreaks in cormorants in North America were first
reponed in 1 9 9 0 in Alberta, Saskatchewan and Manitoba in
Canada (114). In 1992, the disease re-appeared in cormorants
in western Canada, around the Great Lakes, and in the
northern Midwest of the United States of America (USA), in
the latter case spreading to domestic turkeys ( 5 6 , 7 8 ) .
Antigenic and genetic analyses of the viruses suggested that all
the 1 9 9 0 and 1 9 9 2 viruses were very closely related, despite
the geographical separation of the hosts. Since these outbreaks
affected birds that would follow different migratory routes,
the initial infection is thought to have occurred at a mutual
wintering area in Central America. Disease in double crested
cormorants was observed again in Canada, in 1995 and in
California in 1997. In both instances, NDV was isolated from
dead birds, and as previously, the viruses appeared to be
closely related (70).
Caged
'pet
birds'
Virulent NDV isolates have often been obtained from captive
caged birds (103). Kaleta and Baldauf suggested that
infections of recently imported caged birds were unlikely to
have resulted from enzootic infections in feral birds in the
countries of origin (64). The infections were considered likely
to have originated at holding stations before export, either as a
result of enzootic NDV at those stations or of spread from
nearby poultry such as backyard chicken flocks. Panigrahy e£
al. described outbreaks of severe ND in pet birds in six States
of the USA in 1991 (89). Illegal importations were assumed to
be responsible for the introductions of the virus.
Domestic
poultry
Virulent NDV strains have been isolated from all types of
commercially reared poultry, ranging from pigeons to
ostriches.
Racing
and show
pigeons
In the late 1970s, an NDV strain named PPMV-1, showing
some antigenic differences from classical strains, appeared in
pigeons, probably arising in the Middle East. In Europe, the
strain was first reported in racing pigeons in Italy in 1981 (30)
and subsequently produced a true panzootic, spreading in
racing and show pigeons to all parts of the world (8).
Host range of other avian paramyxoviruses
The known host range of each of the other serotypes of APMV
is more restricted than that of NDV (Table I). Viruses of
serotypes APMV-4, APMV-8 and APMV-9 appear to be
restricted to infections of ducks and geese. Similarly, APMV-6
viruses have been isolated frequently from feral ducks and
geese, in which viruses of this serotype appear to be enzootic.
Avian paramyxovirus serotype 6 viruses have also been
isolated from rails that presumably may have had contact with
ducks and geese; spread to turkeys has also been recorded.
Avian paramyxovirus serotype 5 viruses were restricted to
isolations made during a single epizootic in budgerigars in
Japan between 1 9 7 4 and 1 9 7 6 (81), but more recently,
similar viruses have been isolated from budgerigars in Great
Britain (52). Species of psittacines closely related to
budgerigars may also be infected.
The naturat hosts for APMV-7 viruses appear to be pigeons
and doves (species of the order Columbiformes). However,
infections of turkeys ( 1 0 0 ) and ostriches ( 1 1 5 ) have recently
been reported. Presumably, these infections resulted from
contact with pigeons or doves.
Avian paramyxovirus serotype 2 viruses have been isolated
from both chickens and turkeys in association with
respiratory disease. However, the primary natural host
appears to be small perching birds of the order Passeriformes.
Other species have been reported to be infected, including
captive caged psittacines that have usually been in contact
with caged passerines.
448
Avian paramyxovirus serotype 3 viruses can be divided into
two antigenically distinguishable groups. The first has only
been reported to infect turkeys. In experiments, chickens have
been demonstrated to be susceptible to infection, but no
natural infections have been reported. Viruses of the second
group have been isolated frequently from captive caged
psittacines and passerines. The evidence suggests that these
APMV-3 viruses primarily infect psittacine species but will
spread to passerines placed in contact. No isolations of
APMV-3 viruses have been reported from feral birds.
Geographical distribution
Rev. sci. tech. Off. int. Epiz., 19
caged birds in all countries that monitor such birds. Avian
paramyxovirus serotype 2 viruses have been isolated in
surveys of passerine birds in countries of Eastern and Western
Europe, the Middle East, South-East Asia, Africa and Central
America, essentially wherever surveillance of passerine species
has been undertaken. In poultry, APMV-2 viruses have been
isolated from chickens and/or turkeys in countries of Europe
(Eastern and Western), Asia, the Middle East, North and
Central America. The APMV-3 subserotype infecting turkeys
has been isolated only in countries of Western Europe and
North America, but these countries represent the primary
producers of turkeys.
Newcastle disease virus
In many respects, estimations of the geographical distribution
of NDV in domestic poultry are confused by the use of live
vaccines in all but a few countries throughout the world. In
addition, in many countries, a distinction is made between the
disease situation in large scale commercial poultry and in
village chickens. When countries or areas are declared free of
ND, further complications are caused by the definition of the
type of ND viruses described within the claim of 'freedom'.
Even in Australia, which was free of the virulent virus between
the 1 9 3 2 outbreak (2) and the 1 9 9 8 outbreaks, commercial
poultry flocks were frequently found to be infected with
viruses similar to those placed in the 'asymptomatic enteric'
pathotype group ( 1 0 5 , 113). Similarly, on the island of
Ireland, which had long been recognised as free of ND,
monitoring surveys often reveal symptomless infections,
presumably due to spread from waterfowl, and occasional
epizootics of virulent infections occur (87).
The severe form of ND is undoubtably a serious problem
either as an enzootic disease or as a cause of regular, frequent
epizootics throughout Africa, Asia, Central America and parts
of South America (43, 9 9 , 1 0 6 ) .
In other areas such as Europe, the situation appears to be one
of sporadic epizootics occurring despite vaccination
programmes (65).
Current distribution
Newcastle disease
Assessment of the prevalence of ND in the world at any given
time is extremely difficult. In some countries or areas, disease
is not reported at all or only reported if outbreaks occur in
commercial poultry, while the presence of disease in village
chickens or backyard flocks is ignored. Even in commercially
reared poultry, estimations of the geographical distribution of
NDV are confused by the use of live vaccines in all but a few
countries throughout the world. In some countries, the
distribution is especially confused by the use as live vaccines
of viruses that would be considered sufficiently virulent in
other countries to be defined as ND when infecting poultry.
In Western Europe, reported outbreaks increased markedly
during the early 1990s, peaking at 2 3 9 outbreaks in countries
of the European Union (EU) in 1 9 9 4 . The distribution with
time suggested a single epidemic during the early to
mid-1990s, but in fact, antigenic and phylogenetic evidence
indicates that several strains of virus were responsible for
these outbreaks.
Between 1991 and 1995, the majority of outbreaks in the EU
occurred in the Benelux countries and
Germany,
predominantly in backyard poultry. Most of the outbreaks
since 1 9 9 5 have also been in backyard poultry.
Other avian paramyxoviruses
The countries in which each of the APMV serotypes has been
isolated from the various types of avian hosts have been listed
by Alexander (7). Viruses of the serotypes isolated regularly
from migratory ducks and geese (i.e. APMV-4 and APMV-6)
appear to be ubiquitous and distributed world-wide. Fewer
isolations of APMV-8 viruses have been recorded, but the
presence of this serotype in migratory waterfowl in the USA
and Japan is an indication that these too may have a
world-wide distribution. Isolation of APMV-7 viruses from
feral and/or captive pigeons and doves in Japan, the USA and
England (18) again suggests that infections of viruses of this
serotype may occur throughout the world.
Avian paramyxovirus serotype 2 and APMV-3 viruses both
appear to have a world-wide distribution in varying hosts.
Viruses of both serotypes have been isolated from captive
One notable aspect of the outbreaks in Western Europe
during the 1990s was the occurrence of outbreaks in
countries which had been free of the disease for many years.
Since 1 9 9 5 , eighteen outbreaks have been reported in
Denmark, one in Sweden, two in Finland, one in Norway, one
in the Republic of Ireland and twenty-six in Northern Ireland,
all areas of Western Europe that had been declared free of ND
and which were monitored regularly by serological testing
with no evidence of ND virus infections.
Although voluntary vaccination was permitted, Great Britain
was also essentially free of ND, and the outbreak confirmed in
pheasants in 1 9 9 6 was the first in this country since 1984
(20). That outbreak and those in Great Britain in 1 9 8 4 (15)
were shown to b e caused by the variant NDV responsible for
the panzootic in racing pigeons (PPMV-1) that had reached
449
Rev. sci. tech. Off. int. Epiz., 19 (2)
Great Britain in 1 9 8 3 ( 1 3 ) . This virus is still detected
occasionally in racing and feral pigeons. However, in 1 9 9 7 ,
eleven outbreaks of ND were confirmed in Great Britain in
commercial poultry, four in broiler chickens and seven in
turkeys ( 2 2 ) . Although the viruses isolated were highly
virulent for chickens infected in the laboratory, the clinical
disease signs seen in field infections were variable and not
always associated with high mortality, especially in turkeys.
Epidemiological investigations indicated that the majority of
the outbreaks occurred as a result of secondary spread by
human agency from two or more primary infected flocks.
Outbreaks were caused by similar viruses in countries of
Scandinavia in 1 9 9 6 ( 2 3 ) . These outbreaks, linked to the
unusual patterns of movement of migratory birds at the end of
1996 and beginning of 1 9 9 7 , suggested that migratory birds
may have been responsible for the primary introduction of the
causative virus into Great Britain (22).
The first explanation remains a possibility. Some consider that
the disease is unlikely to have gone unreported if it was
enzootic in village chickens, but even at present, village
chickens throughout Africa, Asia and the Americas often show
high levels of mortality, either regularly or as large die-offs
every few years which largely go undiagnosed. Similarly,
occasional descriptions of disease outbreaks prior to 1 9 2 6 are
very similar to ND.
Until recent years, the second explanation has been the one
generally accepted to be most likely. This was fed by the
finding, during the panzootic of 1 9 7 0 - 1 9 7 3 , that movement
of captive caged birds, particularly psittacines, which may be
resistant excreters of NDV, was to some extent responsible for
the introduction and spread of NDV in some countries, and
most noticeably in
California ( 5 0 , 1 1 2 ) . However,
as
discussed above, viruses isolated from feral birds are usually
Until 1998, Australia had been free of virulent NDV since the
1932 outbreak (2). Since 1 9 6 6 , viruses similar to those placed
in the 'asymptomatic enteric' pathotype group ( 1 0 5 , 1 1 3 ) had
been recognised in wild birds in Australia, and on occasions
had spread to commercial poultry flocks. Two outbreaks of
virulent ND occurred in Australia in 1 9 9 8 and further
outbreaks were reported in 1 9 9 9 .
of low virulence and caged birds are most probably infected
after trapping. Maintenance of virus in any species of feral bird
that is at all affected by the virus seems unlikely due to the
likely effect of infection on the survival of the bird.
The
third
explanation has
usually
been
dismissed
as
representing too large a mutation to be within the bounds of
probability of occurring, especially without any apparent
Other avian paramyxoviruses
As discussed above, the most recent developments
concerning other APMVs were the isolation of APMV-7
viruses from ostriches ( 1 1 5 ) and turkeys ( 1 0 0 ) . Until these
reports, natural infections with APMV-7 viruses had been
detected only in pigeons and doves. Recent reports of other
APMVs are scarce, although investigations of poultry and
other birds for other reasons suggest that the distribution and
host range of the other APMVs remains constant.
evolutionary
advantage
that
would
result
in selection.
However, viruses isolated from ND outbreaks in Ireland and
Australia during the 1990s have suggested that some virulent
NDVs may emerge this way.
In Ireland in 1 9 9 0 , two outbreaks of ND occurred in egg
laying birds. The viruses isolated were highly virulent and
apparently identical ( 1 9 ) . Interestingly, these viruses were
very closely related antigenically and genetically ( 4 0 ) to
viruses
of tow virulence normally
isolated
from
feral
Origins of virulent Newcastle disease viruses
waterfowl, but known to have infected chickens on the island
The emergence of ND as a highly pathogenic disease of
poultry in 1 9 2 6 , initially predominantly in South-East Asia,
suggested that a sudden major change had occurred either in
the virus or hosts, although earlier outbreaks may have been
confused with HPAI. Hanson (55) considered that the various
hypotheses proposed could be grouped in three categories, as
follows:
was both antigenically and genetically distant from all other
a) the virulent virus has always existed in poultry in
South-East Asia, but the disease with its enormous economic
impact was only recognised as a significant problem when the
commercialisation of the poultry industry commenced in that
part of the world
the virulent viruses originally arose by mutation
of Ireland in 1 9 8 7 (76). The group formed by these viruses
ND viruses. Collins et al. had shown that the virulent 3 4 / 9 0
virus had four nucleotide differences at the site coding for the
F 0 cleavage site compared to the related viruses of low
virulence (Table II), which would explain the higher virulence
for chickens ( 3 8 ) . However, while the distinctiveness of this
group of viruses from other NDVs supports the theory that
from
those of
low virulence, the mechanism by which this may have
occurred is not at all clear.
Phylogenetic studies have shown all the virulent viruses
b) the virus was enzootic in different species, possibly
inhabiting tropical rain forests, and spread to domestic
poultry due to the incursion of man into that habitat
responsible for the outbreaks in Australia in 1 9 9 8 and 1999 to
c) a major mutation occurred in a precursor virus of low
which in this instance required only two point mutations
virulence.
(Table III).
be extremely closely related to each other and to the endemic
virus of low virulence, suggesting emergence by mutation,
Rev. sci. tech. Off. int. Epiz., 19
450
Table II
Nucleotide/amino acid sequences at FO cleavage site of a virus of high
virulence (34/90) isolated from poultry in Ireland compared to an
antigenically and genetically closely related virus of low virulence
isolated from ducks
Virus
Virulence
MC110
Low
Nucleotide/amino acid sequence at FO
cleavage site
GAA CGG CAG GAG CGT CTG
ERQER*L
112
34/90
High
117
AAA CGG CAG AAG CGTTTT
KRQKR*F
112
If virulent ND strains can emerge from those of low virulence
by mutation, this may have important repercussions on the
current philosophy on control of ND, not least in view of the
enormous quantities of live vaccines used throughout the
world. However, no evidence exists to suggest that the
licensed lentogenic vaccines have mutated and become
virulent strains.
Table III
Nucleotide/amino acid sequence at FO cleavage site of viruses of high
and low virulence isolated in Australia in 1998
Virus
Virulence
Nucleotide/amino acid sequence at FO
cleavage site
1154/98
Low
GGA AGG AGA CAG GGG CGT CTT
1249/98
High
High
111
117
111
117
GRRQGR*L
GGA AGG AGA CAG AGG CGT TTT
GRRQRR*F
GGA AGG AGA CAG AGG CGT TTT
GRRQRR*F
111
Primary and secondary introduction
117
If mutations to virulence do occur, it is not clear whether
these take place in feral birds and then pass to poultry, or
occur once the virus has been introduced in poultry.
However, the lack of virulent isolations from feral birds
suggests that the latter is more likely.
1238/98
susceptible birds in this way, even over short distances. The
success of this route of transmission will depend on many
environmental factors, such as temperature, humidity and
stocking density. In contrast, transmission of virus infection
from one bird to another via contaminated faeces can be easily
demonstrated. The pigeon variant virus, the 'asymptomatic
enteric' viruses, and other viruses which fail to induce
significant respiratory signs in infected birds, are likely to be
transmitted primarily in this way (11, 13).
117
Introduction and spread
Investigation into the epidemiology of avian paramyxoviruses
other than APMV-1 that infect poultry has been limited. The
similarities to APMV-1 in infection and replication suggest
that the same mechanisms and risks will apply.
Transmission between birds
Excluding predatory birds or the feeding of untreated swill
containing poultry meat to poultry, spread from bird to bird
appears to occur as the result of either inhalation of excreted
droplet particles or the ingestion of infective material such as
faeces. Although the administration of live vaccines by aerosol
demonstrates clearly that infection may be established via the
respiratory route, remarkably little experimental evidence
exists to suggest that infected birds will pass on the virus to
Several reviews have dealt with the way in which NDV may be
introduced into a country or area and then subsequently
spread from flock to flock (3, 8, 7 1 , 7 2 ) . The main methods
by which virus can be spread are summarised below.
M o v e m e n t of live b i r d s
Migratory feral birds may be responsible for the primary
introduction of infection, but nearly all NDV isolates obtained
from feral birds are of low virulence. A more significant role of
such birds may be the transmission of virus within an area
following NDV infection of poultry. Exceptions to the
presence of virus of low virulence in migratory birds have
been discussed in the section entitled 'Host range'.
World trade in captive caged birds is enormous, and in many
countries virulent NDV has been isolated frequently from
such birds held in quarantine. For example, 147 virulent
NDV isolations were made from 2 , 2 7 4 lots of captive birds
held in quarantine in the USA from 1974 to 1981 (103). Some
infected psittacines have been shown to excrete virulent virus
intermittently for extremely long periods, in some cases for
more than one year ( 4 8 ) , which further emphasises the
potential role these birds may have in the introduction of
NDV to a country or area.
Game birds may also be implicated in the introduction of
NDV to a country, since considerable international trade
occurs in these birds, which are often imported for immediate
release.
The potential for racing pigeons to carry and introduce NDV
into a country or area has been highlighted by the panzootic
in such birds since the early 1980s.
Trade in backyard flocks and other birds kept for recreational
purposes (hobby birds) has been implicated in the
introduction and spread of ND in the outbreaks in countries
of the EU from 1991 to 1 9 9 4 .
Modern methods of slaughter of commercial poultry,
marketing of poultry meat and veterinary inspection, have
reduced the movement of live commercial poultry (excluding
day-old chicks) in many developed countries. However, in
many countries, the normal method of trade is by five poultry
markets. Such markets, where birds of many different species
451
Rev. sci. tech. Off. int. Epiz., 19 (2)
may be placed in close contact, represent ideal reservoirs of
virus from which disease may be disseminated.
Movement of people and equipment
Secondary spread during most epizootics of ND in recent
years has been the result of the movements of personnel or
equipment. Humans may be infected with NDV, but the most
likely role of personnel is in the transfer of infective faeces
from one site to another on hair, clothing, footwear, crates,
feed sacks, egg trays or vehicles.
Movement of poultry products
In the past, poultry meat has been incriminated as the main
vehicle for the introduction and spread of NDV. For example,
in 1947, one-third of the first 5 4 2 outbreaks in England and
Wales were considered to be directly attributable to feeding
poultry waste to chickens (51). Sampling of batches of frozen
poultry imported into Great Britain in the same year produced
an isolation rate of up to 6 6 % ( 9 4 ) . Modem methods of
poultry carcass preparation and legislation on the feeding of
untreated swill to poultry have greatly diminished the risk
from poultry products, but the possibility of spread in this
way nevertheless remains.
Contaminated poultry food or w a t e r
In countries of the British Isles, outbreaks of ND in
commercial poultry have been associated with feed
contaminated with infective faeces from feral pigeons infected
with NDV ( 1 5 , 8 7 ) . Similarly, water contaminated with
infective faeces may introduce NDV to a flock.
Airborne spread
In recent years, the significance of airborne transfer of virus
has been the subject of some debate. During the 1960s and
1970s, this was considered a major method of spread and
Smith considered it the most logical explanation of spread in
outbreaks occurring in 1 9 6 0 and 1 9 6 2 in Great Britain (104).
In the same country, Dawson considered windborne spread
to be of major significance during the outbreaks of 1 9 7 0 - 1 9 7 2
that were noted for severe respiratory signs and unusual
patterns of spread ( 4 4 ) . However, in the epizootic of
1971-1973 in California, with ostensibly the same virus,
respiratory signs were not especially prominent and Utterback
and Schwartz considered airborne spread to be of low
significance ( 1 1 0 ) .
Few studies have attempted to assess the survival of airborne
virus, but Hugh-Jones et al. were able to detect virus 6 4 m but
not 165 m downwind of an infected premises ( 5 8 ) . These
authors stressed the importance of environmental conditions,
particularly relative humidity, on the likelihood of airborne
spread.
When climatic conditions are favourable and poultry farms
sufficiently concentrated, as in Northern Ireland in 1 9 7 3 , it is
difficult not to conclude that airborne spread may play a
significant role in epidemics of ND ( 7 4 ) . However, in the
majority of outbreaks there has been no evidence that
airborne spread has played á major role and in recent years
airborne spread has not been an issue in reported outbreaks
and an alternative, more likely, cause has nearly always
existed, particularly the movement of poultry and the agency
of humans.
Vaccines
Good manufacturing practices should ensure that vaccines are
highly unlikely to be carriers of virulent NDV. However, in
the past, birds have become infected when vaccines against
other diseases have been contaminated with NDV, or as a
result of failure to inactivate killed vaccines prepared from
virulent NDV. In 1 9 9 6 and 1 9 9 7 , a series of NDV isolates of
low virulence were obtained from poultry flocks in Denmark,
a country which pursues a non-vaccinating policy for ND.
These viruses were demonstrated to be the result of
contamination of avian virus vaccines with vaccinal NDVs
(63). This episode further emphasises the potential for spread
of ND in this way.
Non-avian hosts
Non-avian species are likely to introduce NDV by mechanical
transfer of infective faeces, e.g. by insects, rodents or
scavenging animals. In hot countries, reptiles which may
enter poultry houses should not be ignored as potential
transmitters of NDV, as susceptibility to infection has been
reported in reptiles.
Diagnosis
The diagnostic methods described in this section are primarily
those recommended by the OIE for ND. Diagnosis of other
APMVs is essentially similar. Avian paramyxovirus infections
have usually been diagnosed by serology or virus isolation. In
common with ND, antibodies to APMVs may be detected by
HI tests using the relevant antigens and controls. Avian
paramyxoviruses can be isolated from tracheal or faecal swabs
or tissue samples from infected birds by inoculation of eightto ten-day-old embryonating chicken eggs via the allantoic
cavity. Confirmation of the virus as belonging to the APMV
serotype can be performed by HI tests with specific antiserum.
Definition of Newcastle disease
Although the vast majority of birds are likely to be susceptible
to infection with NDVs of both high and low virulence for
chickens, the disease seen with any given virus may vary
enormously from one species to another.
The clinical signs seen in birds infected with NDV vary widely
and are dependent on factors such as the virus, host species,
age of host, infection with other organisms, environmental
stress and immune status. In some circumstances, infection
with the extremely virulent viruses may result in sudden, high
mortality with comparatively few clinical signs. Thus, the
clinical signs are variable and influenced by other factors so
that none can be regarded as pathognomonic. As discussed
452
Rev. sci. tech. Off. int. Epiz., 19 (2)
above, virulent viruses have been divided into those in which
the predominant signs produced in infected chickens are
intestinal lesions (termed viscerotropic) and those that induce
mainly neurological signs (neurotropic). However, in practice
such distinctions are not clear cut and may be affected by
other factors. Some viruses produce only mild respiratory
disease (lentogenic), and others replicate in the intestine with
little or no clinical signs (asymptomatic enteric). Viruses in
these last two categories are widely used as live vaccines
against ND.
Samples from live birds should include both tracheal and
cloacal swabs, the latter should be visibly coated with faecal
material. Swabbing may harm small delicate birds, but the
collection of fresh faeces may serve as an adequate alternative.
Newcastle disease viruses show a considerable range of
virulence for susceptible hosts such as chickens. In tests used
to assess virulence, variation generally consists of clusters
around the two extremes, but for a variety of reasons, some
viruses may show intermediate virulence (mesogenic).
Equally, the very virulent viruses may infect and replicate in
vaccinated birds without causing clinical disease (35, 5 3 , 9 0 ) .
The samples should be placed in phosphate buffered isotonic
saline (PBS) at pH 7.0-7.4 containing antibiotics. The
antibiotics can be varied according to local conditions but
could contain penicillin (2,000 units/ml), streptomycin
(2 mg/ml), gentamycin (0.05 mg/ml) and mycostatin
(1,000 units/ml) for tissues and tracheal swabs, but at
concentrations 5-fold higher for faeces and cloacal swabs. The
pH of the solution must be adjusted to pH 7.0-7.4 following
the addition of the antibiotics. Faeces and finely minced
tissues should be prepared as 1 0 % - 2 0 % (w/v) suspensions in
the antibiotic solution. Suspensions should be processed as
soon as possible after 1 h-2 h at room temperature. Where this
is impracticable, samples may be stored for up to several days
at 4°C.
This enormous variation in virulence and clinical signs means
that careful definition of what constitutes ND is necessary for
the purposes of trade, control measures and policies.
At the 67th General Session of the OIE held in Paris in May
1999, Resolution No. XIII was to amend the definition of ND
in the Manual of Standards for Diagnostic Tests and Vaccines,
Chapter 2.1.15. on Newcastle disease, as follows:
'Newcastle disease issdefined as an infection of birds caused by
a virus of avian paramyxovirus serotype 1 (APMV-1) that
meets one of the following criteria for virulence:
a) The virus has an intracerebral pathogenicity index (ICPI)
in day-old chicks (Gallus gallus) of 0.7 or greater.
Or
b) Multiple basic amino acids have been demonstrated in the
virus (either directly or by deduction) at the C-terminus of the
F2 protein and phenylalanine at residue 117, which is the
N-terminus of the F1 protein. The term 'multiple basic amino
acids' refers to at least three arginine or lysine residues
between residues 113 to 116. Failure to demonstrate the
characteristic pattern of amino acid residues as described
above would require characterisation of the isolated virus by
an ICPI test.
In this definition, amino acid residues are numbered from the
N-terminus of the amino acid sequence deduced from the
nucleotide sequence of the F 0 gene, 1 1 3 - 1 1 6 corresponds to
residues - 4 to - 1 from the cleavage site' (86).
Where opportunities of obtaining samples are limited, it is
important that cloacal swabs (or faeces) and tracheal swabs
(or tracheal tissue) are examined in addition to organs or
tissues that are grossly affected or associated with clinical
disease.
The supernatant fluids of faeces or tissue suspensions
obtained through clarification by centrifugation at 1,000 g are
inoculated into the allantoic sac of at least five embryonated
SPF chicken eggs of nine to eleven days incubation. After
inoculation, these eggs are incubated at 35°C-37°C for four to
seven days. Eggs containing dead or dying embryos as they
arise, and all eggs remaining at the end of the incubation
period, should first be chilled at 4°C and the allantoic fluids
tested for haemagglutination (HA) activity. Fluids that give a
negative reaction should be passaged into at least (one further
batch of eggs.
Haemagglutination activity detected in bacteriologically sterile
fluids harvested from inoculated eggs may be due to the
presence of any of the fourteen haemagglutinin subtypes of
influenza A viruses or of the eight other APMV serotypes.
Newcastle disease virus can be confirmed by the use of
specific antiserum in an HI test. Usually chicken antiserum is
used, prepared against one of the strains of NDV.
Cross-reactions in HI tests between NDV and APMVs,
particularly APMV-3 may cause some problems which can be
resolved by the use of suitable antigen and antiserum controls
Diagnostic tests
Identification of the agent
Pathogenicity indices
Samples from dead birds should consist of oro-nasal swabs, as
well as samples collected from lung, air sac, intestine
(including contents), spleen, brain, liver and heart tissues.
These may be collected separately or as a pool.
The extreme variation in virulence of different NDV isolates
and the widespread use of live vaccines means that the
identification of an isolate of NDV from birds showing clinical
signs does not confirm a diagnosis of ND. As indicated in the
453
Rev. sci. tech. Off. int. Epiz., 19 (2)
definition, an assessment of the virulence of the isolate by ICPI
test or amino acid sequencing is also required.
The intracerebral pathogenicity index (ICPI) test should be
done as follows:
- fresh infective allantoic fluid with an HA titre of greater
than 2 (1/16) is diluted 1/10 in sterile isotonic saline, with no
additives
4
- 0.05 ml of the diluted virus is injected intracerebrally into
each of ten one-day-old chicks hatched from an SPF flock
- the birds are examined every 2 4 h for eight days
- at each observation the birds are scored: 0 if normal, 1 if
- place 0.025 ml of virus suspension (i.e. infective allantoic
fluid) in the first well. For accurate determination of the HA
content, this should be from a close range of an initial series of
dilutions, i.e. 1/3, 1 / 4 , 1 / 5 , 1 / 6 , etc.
- two-fold dilutions of 0.025 ml amounts of the virus
suspension are made across the plate
- dispense a further 0 . 0 2 5 ml of PBS to each well
- dispense 0.025 ml of 1% v/v chicken red blood cells to each
well
- mix by tapping the plate gently and allow RBC to settle for
approximately 4 0 minutes (either at room temperature or 4°C
if ambient temperatures are high) when control RBC should
be settled to a distinct button
A
sick, and 2 if dead
- the ICPI is the mean score per bird per observation over the
eight-day period.
The most virulent viruses will give indices that approach the
maximum score of 2.0, whereas lentogenic strains will give
values close to 0.0.
- haemagglutination is determined by tilting the plate and
observing the presence or absence of tear-shaped streaming of
the red blood cells. The titration should be read to the highest
dilution giving complete haemagglutination (no streaming);
this represents 1 HA unit (HAU) and can be calculated
accurately from the initial range of dilutions.
The HI test should be done as follows:
Serological tests
Newcastle disease virus may be employed in a wide variety of
serological tests as an. antigen, enabling neutralisation or
enzyme-linked immunosorbent assays (ELISA) to be used for
diagnosis. At present, the HI test is most widely used. Chicken
sera rarely give non-specific positive reactions in this test and
any pre-treatment o f sera is unnecessary. Sera from species
other than chickens may sometimes cause agglutination of
chicken red cells, so this property should first be determined
and then removed by absorption of the serum with chicken
red cells.
Variations of the procedures for HA and HI tests are practised
in different laboratories. Examples are given in Chapter
2.1.15. of the Manual of Standards for Diagnostic Tests and
Vaccines, as presented below (85).
fa
The following examples apply in the use of V-bottomed
microwell plastic plates in which the final volume for both
types of test is 0.075 ml. The reagents required for these tests
are isotonic saline buffered with phosphate (0.1M) to
pH 7.0-7.2 (PBS) and red blood cells (RBC) taken from a
minimum of three SPF chickens and pooled into an equal
volume of Alsever's solution (if SPF chickens are not available,
blood may be taken from unvaccinated birds regularly
monitored and shown to be free of antibodies to NDV). Cells
should be washed three times in PBS before use as a 1%
(packed cell v/v) suspension. Positive and negative control
antigens and antisera should be run with each test, as
appropriate.
The HA test should be done as, follows:
- dispense 0.025 ml of PBS into each well of a plastic
microtitre plate (V-bottomed)
- dispense 0.025 ml of PBS into each well of a.plastic
microtitre plate (V-bottomed)
- place 0.025 ml of serum into first well of plate
- make two-fold dilutions of 0.025 ml amounts of the serum
across the plate- add 4 HAU of virus/antigen in 0.025 ml to each well and
leave for a minimum of 3 0 minutes at room temperature or
60 minutes at 4°C
- add 0.025 ml of 1% v/v chicken RBC to each well and after
gentle mixing allow RBC to settle for approximately
4 0 minutes (either at room temperature or 4°C if ambient
temperatures are high) when control RBC should be settled to
•a distinct button
- the HI titre is the highest dilution o f serum causing
complete inhibition of 4 HAU of antigen. The agglutination is
assessed more exactly by tilting the plates. Only those wells in
which the red cells 'stream' at the same rate as the control
wells (containing 0 . 0 2 5 ml RBC and 0 . 0 5 ml PBS only) should
be considered as showing inhibition
- the validity of results should be assessed against a negative
control serum, which should not give a titre > 2 and a.positive
control serum for which/ the titre should be within one
dilution of the known titre..
2
The value of serology in diagnosis is clearly related to the
immune status of the affected birds. Haemagglutination
inhibition titres may be regarded as positive if inhibition
occurs at a serum dilution of 1/16 ( 2 ) or more against 4 HAU
of antigen.
4
Haemagglutination inhibition titres may be used to assess the
immune status, of a flock. In vaccinated flocks that are being
monitored serologically, anamnestic responses may be
Rev. sci. tech. Off. int. Epiz., 19 (2)
454
observed as the result of a challenge infection with field virus
(24), but great care should be exercised as variations may
occur from other causes. For example, APMV-3 virus
infections
of NDV-vaccinated
turkeys
have
been
demonstrated to result in substantially increased titres to NDV
(10).
Other diagnostic methods
Nucleotide
policies. Vaccinal viruses are somewhat different, as some are
sufficiently virulent to cause disease in fully susceptible birds.
In some countries, legislation is designed to reduce the
likelihood of outbreaks from specific sources. For example,
on the island of Ireland, legislation requires that poultry feed
is heat-treated to reduce the possibility of introduction of
NDV by this, route.
sequencing
The knowledge that the virulence of NDV strains is primarily
dependent on the amino acid sequence at the FO cleavage site
has led to several suggestions for in vitro tests based on
detection of the nucleotide sequence coding for the FO
cleavage site to replace the in vivo pathogenicity tests. Studies
have been performed using molecular techniques to
determine the FO cleavage site sequence by reverse
transcription polymerase chain reaction either on the isolated
virus or on tissues and faeces from infected birds (62, 6 6 , 8 4 ,
102). In other studies, oligonucleotide probes tailored to the
FO cleavage site have been used to detect NDV in tissues and
differentiate between viruses of high or low virulence by
hybridisation techniques (59, 8 3 ) . With both these
approaches, problems relating to mismatching of the primers
or probes or mixtures of virulent and avirulent viruses mean
that, at present, these in vitro techniques cannot wholly
replace the in vivo ICPI test.
Monoclonal antibodies
Mouse mAbs directed against strains of NDV have been used
in HI tests to allow rapid identification of NDV without the
possible cross reactions with other PMV serotypes that may
occur with polyclonal sera (6).
Some workers have used mAbs to distinguish between
specific viruses. For example, two groups have described
mAbs which distinguish between the common vaccine
strains, Hitchner B l and La Sota (47, 77), while other mAbs
can separate vaccine viruses from epizootic virus in a given
geographical area (108).
Panels of mAbs have been used to establish antigenic profiles
of NDV isolates based on their ability to react or not with the
viruses. This has proven to be a valuable method for grouping
and differentiating isolates of NDV which has been
particularly valuable in understanding the epizootiology of
outbreaks (20, 2 1 ) .
Control
Newcastle disease
Policies
In countries or areas that are free of ND, the primary aim
should be to prevent the introduction of the virus. As
migratory and other feral birds frequently carry NDV strains
of low virulence, which occasionally spread to domestic
poultry, such viruses are usually excluded from control
On farms, control measures should attempt to prevent virus
from infecting the flock. The practice of good hygiene and
biosecurity measures aimed at preventing the introduction of
virus by the routes described above is of paramount
importance on poultry farms.
Biosecurity aimed at preventing disease should commence at
the planning stage of commercial poultry farms. Farms and
flocks should be well separated, hatcheries should be isolated
from poultry farms, different species should be reared on
different sites, and an adequate fresh water supply should be
available, preferably one that does not draw on surface water.
On poultry farms, the following points should be observed:
a) bird houses, feed stores and water tanks should be
bird-proofed
b) movements on and off the farm should be kept to a
minimum
c) all equipment, especially vehicles, should be disinfected
before access to the site is permitted
d) movements between different farms for egg collection,
carcass collection, feed delivery and similar should be to and
from a specified collection and delivery point away from the
poultry flocks.
Visits by personnel such as bleeding or vaccination teams,
inseminators and veterinarians are the most likely method of
introduction of ND. If such visits are unavoidable, regimens of
clothing change, equipment disinfection and other basic
hygiene controls must be enforced.
Vaccination
Vaccination must be regarded as complementing good
management, biosecurity and hygiene in rearing domestic
poultry. Vaccination against ND must never be considered an
alternative to these other measures.
Vaccinated birds challenged with virulent NDV may become
infected and excrete virus, although in relatively small
amounts, while remaining apparently healthy ( 5 3 , 9 0 , 110).
This disadvantage must be fully understood when planning
the role of vaccination in the control of ND.
Details of vaccination regimens, methods of administration
and interpretation of antibody titres can be found in the
review by Kouwenhoven (69), the text that follows considers
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Rev. sci. tech. Off. int. Epiz., 19 (2|
the factors leading to the decision to vaccinate and to the
choice of vaccine.
Decision
to
vaccinate
National or international legislation or agreements that give
the farmer and advisers little choice may control vaccination
policies. For example, in the Netherlands vaccination is
compulsory, but in countries such as Finland, Sweden and
Norway vaccination is banned. In countries where legislation
does not enforce vaccination under normal circumstances,
'ring vaccination' may be required should an outbreak occur.
In many countries, severe ND is enzootic, usually in village
chickens at least, and in such high risk areas, vaccination of
commercially reared birds is the only way to reduce the
disease and losses resulting from the inevitable introduction of
virus. In countries where disease is not enzootic, a decision to
include prophylactic vaccination, as part of the control of ND
is not so clear cut, especially when the cost and the possibility
of vaccine reactions are considered. In addition, the existence
of a slaughter policy based on infection rather than disease, as
in the EU (41), would seem a disincentive for routine
vaccination.
Choice of vaccine
Choice of vaccine is governed by three main considerations,
namely:
a) the immunogenicity of the vaccine
b) the type of vaccine (inactivated or live)
c) the virulence of live vaccine strains, not only for the
recipient host species, but also for other species which may
become infected due to lateral spread of the vaccine.
For live vaccines, the likely exacerbation of infections with
other organisms or vaccines must also be considered.
Using modem techniques, considerable antigenic diversity
has been detected in NDV isolates and strains (21). However,
the vaccines commonly in use are capable of producing
antibodies that protect against even those NDV isolates
showing a high degree of antigenic divergence from the
vaccine strain ( 1 6 , 19). Thus, antigenic variation does not
seem to be an important consideration in the choice of
vaccine.
Although inactivated oil emulsion vaccines can be efficacious
if used as primary vaccine (111), the additional cost of these
vaccines, both direct and in administration, means that live
vaccines are usually preferred. Vaccination programmes for
laying birds are usually based on the use of several doses of
live lentogenic vaccine followed by inactivated vaccine at
point of lay.
Mesogenic live vaccines tend to be used only in countries
where virulent NDV is widespread and maintenance of high
antibody titres is important to prevent serious disease. The
presence of enzootic disease is usually linked to severe
economic restrictions, which exclude the use of oil emulsion
vaccine. Mesogenic vaccines may have serious clinical effects
if given to birds which have not been immunised previously
and these vaccines are sufficiently virulent to fall within the
new OIE definition of ND.
The most popular live vaccines have evolved from field
isolates of low virulence. Most are based on the 'lentogenic'
virases Hitchner B l or La Sota or similar viruses, although
some 'asymptomatic enteric' viruses have also been used as
live vaccines. A difficulty associated with live vaccines is that
the immune response appears to be related to the virulence of
the virus strain ( 9 3 ) ; La Sota, for example, gives better
protective antibody titres than Hitchner B l , but is more likely
to cause reactions. The method of application is important.
Individual application methods such as the use of eye drops
and beak dipping are costly; mass application of live vaccine
in generated aerosols or sprays or in drinking water is cheaper
and more convenient. However, sprays and aerosols in
particular may result in severe respiratory reaction and,
especially with La Sota virus, even high mortality.
The choice of vaccine may also be restricted by control
policies, and the Commission of the EU has set criteria
banning the use of live ND vaccines with an ICPI of greater
than 0.4 and inactivated vaccine production from viruses with
an ICPI exceeding 0.7 ( 4 2 ) .
Other avian paramyxoviruses
The risk from APMV-2 virus may be minimised by prevention
of introduction of the virus by bird-proofing poultry houses
and good general hygiene practices. Some success has been
reported in treatment of exacerbating secondary bacterial
infections with antibiotics. Samberg et al. reported good
antibody response in day-old turkeys to an inactivated oil
emulsion APMV-2 vaccine (101).
Avian paramyxovirus serotype 3 virases appear to spread
slowly. However, good hygiene, including careful disinfection
and allowing time between restocking, has not always
prevented infection in subsequent flocks. Inactivated,
oil-emulsion vaccines are available in the USA, the United
Kingdom (UK) and other countries of Europe for use in
turkey breeding flocks. These are usually injected twice, four
weeks apart, before the birds begin to lay ( 3 2 , 4 9 ) . Duchatel et
al. showed that subcutaneous inoculation of parakeets with
APMV-3 vaccine afforded these birds protection from
challenge with APMV-3 virus (46).
Public health
Newcastle disease virus is a human pathogen. In the UK, the
virus is placed in Hazard group 2 of the Advisory Committee
on Dangerous Pathogens (1). The virus is thus considered to
Rev. sci. tech. Off. int. Epiz., 19 (2
456
be: 'A biological agent that can cause human disease and may
be a hazard to employees; it is unlikely to spread to the
community...'.
A review of ND as a zoonosis recorded thirty-five published
reports of ND virus infections of humans between 1 9 4 8 and
1971 (36). Since that time, few additional reports have been
published, which probably reflects the lack of serious, lasting
effects resulting from such infections and the fact that such
infections are commonplace.
Reported infections have not been life threatening and usually
have not been debilitating for more than one or two days. The
most frequently reported and best substantiated clinical signs
in human infections have been eye infections, usually
consisting of unilateral or bilateral reddening, excessive
lachrymation, oedema of the eyelids, conjunctivitis and
sub-conjunctival haemorrhage (36). Although the effect on
the eye may be quite severe, infections are usually transient
and the cornea is not affected.
Human infections with NDV have usually resulted from direct
contact with the virus, infected birds or carcasses of diseased
birds. Human to human spread has never been reported,
although spread by contagion is theoretically possible. The
types of people known to have been infected with NDV
include laboratory workers (usually as a result of accidental
splashing of infective material into the eye), veterinarians in
diagnostic laboratories (presumably as a result of contact with
infective material during post-mortem examinations),
workers in broiler processing plants and vaccination crews,
especially when live vaccines are administrated as aerosols or
fine dust. Pedersden et al. reported significantly higher
antibody titres to NDV in people who had an association with
poultry (92).
No reports exist of other APMV serotypes infecting humans.
However, the potential may exist, and virus of APMV-2
serotype has been isolated from cynomolgus monkeys
(Macaca fascicularis) (82).
Reports of other clinical symptoms in humans infected with
NDV are less well substantiated, but suggest that a more
generalised infection may sometimes occur, resulting in chills,
headaches and fever, with or without conjunctivitis (36). Both
vaccinal strains and strains virulent for poultry may infect and
cause clinical signs in humans.
La maladie de Newcastle et les autres paramyxoviroses aviaires
D.J. Alexander
Résumé
La maladie de N e w c a s t l e , conséquence d'une infection par des paramyxovirus de
sérotype 1 (APMV-1), est inscrite sur la Liste A de l'Office international des
épizooties. Très meurtrière dans le passé, la maladie de N e w c a s t l e pose toujours
d'importants problèmes à l'aviculture industrielle existante o u naissante de
nombreux pays. Elle a une incidence économique élevée, même dans les pays où
elle est pratiquement maîtrisée, en raison des coûts liés à la v a c c i n a t i o n et/ou au
maintien d e mesures rigoureuses d e biosécurité. La v i r u l e n c e v a r i e selon les
souches du virus de la maladie de N e w c a s t l e , et la sensibilité des oiseaux diffère
d'une espèce à l'autre, ce qui entraîne la nécessité de bien définir la maladie
avant toute mesure prophylactique liée aux échanges. Pour confirmer le
diagnostic, il f a u t isoler et caractériser le virus en cause. L'évaluation de la
virulence se fait habituellement par des r e c h e r c h e s in vivo. Cependant, depuis
que la base moléculaire du pouvoir pathogène du virus est mieux c o n n u e , on
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Rev. sci. tech. Off. int. Epiz., 19 (2)
recourt de plus en plus à la caractérisation génétique in vitro. La prophylaxie de la
maladie repose sur des méthodes visant à e m p ê c h e r l'introduction et la
propagation du virus ainsi que sur des bonnes pratiques de biosécurité,
associées ou non à la vaccination. Les virus de la maladie de N e w c a s t l e peuvent
infecter l'homme, provoquant le plus souvent des cas sporadiques de
conjonctivite, mais a u c u n cas de transmission entre êtres humains n'a jamais été
observé.
Huit autres sérotypes de paramyxovirus aviaires ont été r e c o n n u s (APMV-2 à
APMV-9). La plupart de ces sérotypes semblent spécifiques à des espèces
d'oiseaux sauvages qui leur servent de réservoir naturel, mais d'autres espèces
hôtes sont également sensibles. Seuls les virus A P M V - 2 et A P M V - 3 ont eu un
impact sanitaire et économique important sur la production aviaire. Ces deux
types de virus provoquent des maladies respiratoires et une chute de ponte qui
peuvent être graves lorsque d'autres infections ou des f a c t e u r s de stress lié à
l'environnement viennent s'y ajouter. A u c u n e infection naturelle par les virus
A P M V - 3 n'a été signalée chez les volailles.
Mots-clés
Diagnostic - Épidemiologie - Étiologie - Maladie - Maladie de Newcastle - Maladies
aviaires - Paramyxovirus aviaires - Prophylaxie - Santé publique.
•
Enfermedad de Newcastle y otros paramixovirus aviares
D.J. Alexander
Resumen
La enfermedad de N e w c a s t l e , causada por paramixovirus aviares pertenecientes
al serotipo 1 (APMV-1), figura en la Lista A de la Oficina Internacional de
Epizootias. Esta e n f e r m e d a d , que históricamente ha tenido efectos devastadores
sobre las poblaciones de aves de corral, sigue constituyendo en muchos países
uno de los principales problemas que afectan a las explotaciones avícolas, tanto
jóvenes como consolidadas. Incluso en países donde la enfermedad puede
considerarse bajo control, las campañas de v a c u n a c i ó n y/o el mantenimiento de
estrictas medidas de seguridad biológica siguen suponiendo una pesada carga
e c o n ó m i c a . La desigual virulencia que presentan las cepas víricas para las aves
de corral, junto con la distinta susceptibilidad de las diversas especies de aves,
hace necesaria una definición muy cuidadosa de la enfermedad a efectos de
control sanitario y de actividad comercial. Para el diagnóstico de confirmación de
la enfermedad de N e w c a s t l e es preciso aislar y caracterizar el virus de que se
trate. Para evaluar su virulencia suelen ser necesarias pruebas in vivo. Sin
embargo, ahora que se comprenden más cabalmente los mecanismos
moleculares en los que se funda el poder patógeno del virus, se viene usando
cada vez más su caracterización genética in vitro. La lucha contra la enfermedad
integra desde medidas para prevenir la introducción y propagación del virus
hasta buenas prácticas en materia de seguridad biológica y/o v a c u n a c i o n e s .
A u n q u e el virus de la enfermedad de N e w c a s t l e puede afectar al hombre,
causando en general episodios pasajeros de conjuntivitis, no se ha descrito
ningún caso de transmisión entre seres humanos.
Se c o n o c e n otros ocho serotipos de paramixovirus aviares, numerados del
A P M V - 2 al A P M V - 9 . Buena parte de esos serotipos parecen estar presentes en
reservorios naturales de determinadas especies aviares silvestres, aunque hay
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Rev. sci. tech. Off. int. Epiz., 19
otras especies que suelen ser susceptibles y pueden ejercer de huéspedes. Sólo
los serotipos A P M V - 2 y A P M V - 3 han tenido efectos sanitarios y económicos de
cierta importancia para la producción avícola. Ambos tipos de virus provocan
afecciones respiratorias y caídas de la producción de huevos, que pueden
revestir cierta importancia cuando a sus efectos se suman los de otras
infecciones o presiones ambientales. No se ha descrito ningún caso de infección
natural de pollos por virus del tipo APMV-3.
Palabras clave
Control - Diagnóstico - Enfermedad - Enfermedad de Newcastle - Enfermedades aviares
- Epidemiología - Etiología - Paramixovirus aviares - Salud pública.
References
1. Advisory Committee on Dangerous Pathogens (1995). Categorisation of biological agents according to hazard and
categories of containment, 4th Ed. Health and Safety
Executive Books, Sudbury, 152 pp.
10. Alexander D.J., Pattison M. &Macpherson I. (1983).-Avian
paramyxoviruses of PMV-3 serotype in British turkeys. Avian
Pathol, 12, 469-482.
2. Albiston H.E. & Gorrie C.J. (1942). - Newcastle disease in
Victoria. Aust. vet.J., 18, 75-79.
11. Alexander D.J., Parsons G. & Marshall R. (1984). - Infection
of fowls with Newcastle disease vims by food contaminated
with pigeon faeces. Vet. Rec., 115, 601-602.
3. Alexander D J . (1988). - Newcastle disease: methods of
spread. In Newcastle disease (D.J. Alexander, ed.). Kluwer
Academic Publishers, Boston, 257-272.
4. Alexander D.J. (1988). - Preface: methods of spread. In
Newcastle disease (D.J. Alexander, ed.). Kluwer Academic
Publishers, Boston, xi.
5. Alexander D.J. (1990). - Avian Paramyxoviridae - recent
developments. Vet. Microbiol., 23, 103-114.
6. Alexander D.J. (1992). - U s e of monoclonal antibodies in the
diagnosis of Newcastle disease and characterisation of the
virus. In Proc. Commission of the European Communities
workshop on avian paramyxoviruses (E.F. Kaleta &
U. Heffels-Redmann, eds), 27-29 July, Rauischholzhausen,
Germany. Institut für Geflügelkrankheiten, Giessen,
145-156.
7. Alexander D.J. (1993). - Paramyxovirus infections. In Viral
infections of vertebrates, Vol. 3. Viral infections of birds
(M.C. Horzinek, ed.). Elsevier Science Publishers Co.,
Amsterdam, 321-340.
8. Alexander D.J. (1997). - Newcastle disease and other avian
Paramyxoviridae infections. In Diseases of poultry, 10th Ed.
(B.W. Calnek with H.J. Barnes, C.W. Beard, L.R. McDougald
& Y.M. Saif, eds). Mosby-Wolfe, London, 541-570.
9. Alexander D.J. & Allan W.H. (1974). - Newcastle disease
vims pathotypes. Avian Pathol, 3, 269-278.
12. Alexander D.J., Russell P.H. & Collins M.S. (1984). Paramyxovirus type 1 infections of racing pigeons.
1: Characterisation of isolated viruses. Vet. Rec., 114,
444-446.
13. Alexander D.J., Wilson G.W.C., Thain J.A. & Lister S.A.
(1984). - Avian paramyxovirus type 1 infections of racing
pigeons. 3. Epizootiological considerations. Vet. Ree, 115,
213-216.
14. Alexander D.J., Russell P.H., Parsons G., Abu Elzein E.M.E.,
Ballough A., Cernik K., Engstrom B., Fevereiro M.,
Fleury H.J.A., Guittet M., Kaleta E.F., Kihm U., Kosters J.,
Lomniczi B., Meister J., Meulemans G., Nerome K., Petek M.,
Pokomunski S., Polten B., Prip M., Richter R., Saghy E.,
Samberg Y., Spanoghe L. & Tumova B. (1985). - Antigenic
and biological characterisation of avian paramyxovirus type
1 isolates from pigeons - an international collaborative
study. Avian Pathol, 14, 365-376.
15. Alexander D.J., Wilson G.W.C., Russell P.H., Lister S.A. &
Parsons G. (1985). - Newcastle disease outbreaks in fowl in
Great Britain during 1984. Vet. Ree, 117, 429-434.
16. Alexander D.J. & Parsons G. (1986). - Protection of
chickens against challenge with the variant virus responsible
for Newcastle disease in 1984 by conventional vaccination.
Vet. Rec., 118,176-177.
Rev. sci. tech. Off. int. Epiz., 19 (2)
17. Alexander D.J., Manvell R.J., Kemp P.A., Parsons G.,
Collins M.S., Brockman S., Russell P.H. & Lister S.A. (1987).
- Use of monoclonal antibodies in the characterisation of
avian paramyxovirus type 1 (Newcastle disease virus)
isolates submitted to an international reference laboratory.
Avian Pathol, 16, 553-565.
18. Alexander D.J., Manvell R.J., Collins M.S. & Brockman S.J.
(1991). - Evaluation of relationships between avian
paramyxoviruses isolated from birds of the Columbidae
family. Arch. Virol., 114, 267-276.
19. Alexander D.J., Campbell G., Manvell R.J., Collins M.S.,
Parsons G. & McNulty M.S. (1992). - Characterisation of an
antigenically unusual vims responsible for two outbreaks of
Newcastle disease in the Republic of Ireland in 1990. Vet.
Rec., 130, 65-68.
20. Alexander D.J., Manvell R.J., Frost K.M., Pollitt W.J.,
Welchman D. & Perry K. (1997). - An outbreak of
Newcastle disease in pheasants in Great Britain in May 1996.
Vet. Rec., 140,20-22.
21. Alexander D.J., Manvell R.J., Lowings J.P., Frost K.M.,
Collins M.S., Russell P.H. & Smith J.E. (1997). - Antigenic
diversity and similarities detected in avian paramyxovirus
type 1 (Newcastle disease vims) isolates using monoclonal
antibodies. Avian Pathol, 26, 399-418.
22. Alexander D.J., Morris H.T., Pollitt W.J., Sharpe C.E.,
Eckford R.L., Sainsbury R.M.Q., Mansley L.M., Gough R.E.
& Parsons G. (1998). - Newcastle disease outbreaks in
domestic fowl and turkeys in Great Britain during 1997. Vet.
Rec., 143,209-212.
23. Alexander D.J., Banks J . , Collins M.S., Manvell R.J.,
Frost K.M., Speidel E.C. & Aldous E.W. (1999). - Antigenic
and genetic characterisation of Newcastle disease viruses
isolated from outbreaks in domestic fowl and turkeys in
Great Britain during 1997. Vet. Rec., 145, 417-421.
24. Allan W.H., Lancaster J.E. & Toth B. (1978). - Newcastle
disease vaccines - their production and use. Food
Agriculture Organization (FAO) Animal Production Series
No. 10. FAO, Rome, 163 pp.
25. Anderson C , Kearsley R., Alexander D J . & Russel P.H.
(1987). - Antigenic variation in avian paramyxovirus type 3
detected by mouse monoclonal antibodies. Avian Pathol, 16,
691-698.
26. Arias-Ibarrondo J., Mikami T., Yamamoto H., Furuta Y.,
Ishioka S., Okado K. & Sato G. (1978). - Studies on a
paramyxovirus isolated from Japanese sparrow-hawks
(Accipiter virugatus gularis).Jpn. J. vet. Sci., 40, 315-323.
27. Bahl A.K. & Vickers M.L. (1982). - Egg drop syndrome in
breeder turkeys associated with turkey para-influenza
virus-3 (TPIV-3). In Proc. 31st Western Poultry Disease
Conference, Davis, California. University of California,
Davis, 113 pp.
28. Bankowski R.A., Almquist J . & Dombrucki J . (1981). Effect of paramyxovirus Yucaipa on fertility, hatchability and
poult yield of turkeys. Avian Dis., 25, 517-520.
459
29. Beard C.W. & Hanson R.P. (1984). - Newcastle disease. In
Diseases of poultry, 8th Ed. (M.S. Hofstad, H.J. Barnes,
B.W. Calnek, W.M. Reid & H.W. Yoder, eds). Iowa State
University Press, Ames, 452-470.
30. Biancifiori F. & Fioroni A. (1983). - An occurrence of
Newcastle disease in pigeons: virological and serological
studies on the isolates. Comp. Immunol Microbiol infect. Dis.,
6, 247-252.
31. Blaxland J.D. (1951). - Newcastle disease in shags and
cormorants and its significance as a factor in the spread of
this disease among domestic poultry. Vet. Rec., 63, 731-733.
32. Box P. (1987). - PMV-3 disease of turkeys. Int. Hatchery
Pract.,2, 4-7.
33. Box P., Holmes H.C. & Webb K.J. (1988). - Significance of
antibody to avian paramyxovirus 3 in chickens. Vet. Rec.,
121, 423.
34. Bradshaw G.L. & Jensen M.M. (1979). - The epidemiology
of Yucaipa virus in relationship to the acute respiratory
syndrome in turkeys. Avian Dis., 2 3 , 539-542.
35. Capua I., Scacchia M., Toscani T. & Caporale V. (1993). Unexpected isolation of virulent Newcastle disease virus
from commercial embryonated fowls' eggs. J. vet. Med., B, 4 0 ,
609-612.
36. Chang P.W. (1981). - Newcastle disease. In CRC handbook
series in zoonoses. Section B: viral zoonoses. Vol. II
(G.W. Beran, ed.). CRC Press, Boca Raton, Florida, 261-274.
37. Geary L. (1977). - Succès de reproduction du cormoran à
aigrettes, Phalacrocorax auritus auritus, sur trois îles du
St Laurent, en 1975 et 1976. MSc Thesis, University of Laval,
Canada, 1-68.
38. Collins M.S., Bashiruddin J.B. & Alexander D.J. (1993). Deduced amino acid sequences at the fusion protein cleavage
site of Newcastle disease viruses showing variation in
antigenicity and pathogenicity. Arch. Virol, 128, 363-370.
39. Collins M.S., Strong I. & Alexander D J . (1994). - Evaluation
of the molecular basis of pathogenicity of the variant
Newcastle disease viruses termed 'pigeon PMV-1 viruses'.
Arch. Virol, 134, 403-411.
40. Collins M.S., Franklin S., Strong I., Meulemans G. &
Alexander D.J. (1998). - Antigenic and phylogenetic studies
on a variant Newcastle disease vims using anti-fusion protein
monoclonal antibodies and partial sequencing of the fusion
protein gene. Avian Pathol, 27, 90-96.
41. Commission of the European Communities (1992). Council directive 92/66/EEC of 14 July 1992 introducing
Community measures for the control of Newcastle disease.
Off.]. Eur. Communities, L 2 6 0 , 1 - 2 0 .
42. Commission of the European Communities (1993). Commission decision of 8 February 1993 laying down the
criteria to be used against Newcastle disease in the context of
routine vaccination programmes. Off. J. Eur. Communities,
L 5 9 , 35.
.460
43. Copland J.W. (1987). - Newcastle disease in poultry: a new
food pellet vaccine. The Australian Centre for International
Agricultural Research, Canberra, 119 pp.
44. Dawson P.S. (1973). - Epidemiological aspects of Newcastle
disease. Bull. Off. int. Epiz., 79, 27-34.
45. De Leeuw O. & Peeters B. (1999). - Complete nucleotide
sequence of Newcastle disease virus: evidence for the
existence of a new genus within the subfamily
Paramyxovirinae. J. gen. Virol., 80, 131-136.
46. Duchatel J.P., Flore H. & Vindevogel H. (1998). Vaccination de perruches de Bourke [Neophema bourkii)
contre l'infection par le paramyxovirus sérotype 3 au moyen
de vaccins inactivés adjuvés aqueux. Ann. Med. vét., 142,
203-206.
47. Erdei J., Erdei J . , Bachir K., Kaleta E.F., Shortridge K.F. &
Lomniczi B. (1987). - Newcastle disease vaccine (La Sota)
strain specific monoclonal antibody. Arch. Virol., 9 6 ,
265-269.
48. Erickson G.A., Mare C.J., Gustafson G.A., Miller L.D.,
Protor S.J. & Carbrey E.A. (1977). - Interactions between
viscerotropic velogenic Newcastle disease vims and pet birds
of six species. 1. Clinical and serologic responses, and viral
excretion. Avian Dis., 2 1 , 642-654.
49. Eskelund K.H. (1988). - Vaccination of turkey breeder hens
against paramyxovirus type 3 infection. In Proc.
37th Western Poultry Disease Conference, 29 February2 March, Davis, California. University of California, Davis,
43-45.
50. Francis D.W. (1973). - Newcastle and psittacines, 1970-71.
Poult. Digest, 3 2 , 16-19.
51. Gordon R.F., Reid J . & Asplin F.D. (1948). - Newcastle
disease in England and Wales. In Official Report 8th World's
Poultry Congress, Vol. 1, 20-27 August, Copenhagen,
642-650.
52. Gough R.E., Manvell R.J., Drury S.E.N., Naylor P.F.,
Spackman D. & Cooke S.W. (1993). - Deaths in budgerigars
associated with a paramyxovirus-like agent. Vet. Rec., 132,
123.
53. Guittet M., Le Coq H., Morin M., Jestin V. & Bennejean G.
(1993). - Distribution of Newcastle disease virus after
challenge in tissues of vaccinated broilers. In Proc.
10th World Veterinary Poultry Association Congress,
Sydney, 179.
54. Hannoun C. (1977). - Isolation from birds of viruses with
human neuraminidase. Dev. biol. Standard., 39, 469-472.
55. Hanson R.P. (1972). - Newcastle disease. In Diseases of
poultry, 6th Ed. (M.S. Hofstad, ed.). Iowa State University
Press, Ames, 619-656.
56. Heckert R.A. (1993). - Newcastle disease in cormorants.
Can. vet.J.,34, 184.
Rev. sci. tech. Off. int. Epiz., 19
57. Herczeg J., Wehmann E., Bragg R.R., Travassos Dias P.M.,
Hadjiev G , Werner O. & Lomniczi B. (1999). - Two novel
groups (Vllb and VIII) responsible for recent Newcastle
disease outbreaks in Southern Africa, one (Vllb) of which
reached Southern Europe. Arch. Virol, 144, 2087-2099.
58. Hugh-Jones M., Allan W.H., Dark F.A. & Harper G.J.
(1973). - The evidence for the airborne spread of Newcastle
disease. J. Hyg. (Camb.), 71, 325-339.
59. Jarecki-Black J.C. & King D J . (1993). - An oligonucleotide
probe that distinguishes isolates of low virulence from the
more pathogenic strains of Newcastle disease virus. Avian
Dis., 37, 724-730.
60. Jestin V., Cherbonnel M., Morin M., Guittet M. &
Bennejean G. (1989). - Characterisation of French avian
paramyxovirus type 1 (PMV 1) isolates with a panel of
monoclonal antibodies to the Ploufragan strain of Newcastle
disease vims. Arch. Virol., 105, 189-198.
61. Jestin V. & Cherbonnel M. (1992). - Use of monoclonal
antibodies and gene amplification (PCR) for characterisation
of a-PMV-1 strains. In Proc. Commission of the European
Communities workshop on avian paramyxoviruses
(E.F. Kaleta & U. Heffels-Redmann, eds), 27-29 July,
Rauischholzhausen,
Germany.
Institut
für
Geflügelkrankheiten, Giessen, 157-166.
62. Jestin V., Cherbonnel M. & Arnauld C. (1994). - Direct
identification and characteristion of APMV-1 from
suspicious organs by nested PCR and automated sequencing.
In Proc. Joint 1st Annual Meetings of the National Newcastle
Disease and Avian Influenza Laboratories of the European
Communities (D.J. Alexander, ed.), 5-6 October 1993,
Brussels. Commission of the European Communities,
Brussels, 89-97.
63. J0rgensen P.H.Jensen Handber K., Manvell R.J., Frost K.M.
& Alexander D.J. (2000). - Comparison between avian
paramyxovirus serotype 1 isolates of low virulence for
chickens obtained from contaminated poultry vaccines and
from poultry flocks. Vet. Rec. (in press).
64. Kaleta E.F. & Baldauf C. (1988). - Newcastle disease in
free-living and pet birds. In Newcastle disease
(D.J. Alexander, ed.). Kluwer Academic Publishers, Boston,
197-246.
65. Kaleta E.F. & Heffels-Redmann U. (eds) (1992). - Proc.
Commission of the European Communities workshop on
avian paramyxoviruses, 27-29 July, Rauischholzhausen,
Germany. Institut für Geflügelkrankheiten, Giessen, 391 pp.
66. Kant A., Koch G., Van Roozelaar D.J., Balk F. & Ter
Huurne A. (1997). - Differentiation of virulent and
non-virulent strains of Newcastle disease vims within
24 hours by polymerase chain reaction. Avian Pathol, 26,
837-849.
67. King D.J. & Seal B.S. (1997). - Biological and molecular
characterisation of Newcastle disease vims field isolates with
comparison to reference NDV strains. Avian Dis., 42,
507-516.
Rev. sci. tech. Off. int. Epiz., 19 (2)
68. King D.J. & Seal B.S. (1997). - Biological and molecular
characterisation of Newcastle disease virus isolates from
surveillance of live bird markets in the Northeastern United
States. Avian Dis., 4 1 , 683-689.
69. Kouwenhoven B. (1993). - Newcastle disease. In Virus
infections of birds (J.B. McFerran & M.S. McNulty, eds).
Elsevier, Amsterdam, 341-361.
70. Kuiken T. (1998). - Newcastle disease and other causes of
mortality in double-crested cormorants (Phalacrocorax
auritus). PhD thesis, University of Saskatchewan, 174 pp.
71. Lancaster J.E. (1966). - Newcastle disease - a review
1926-1964. Monograph No. 3. Canada Department of
Agriculture, Ottawa, 188 pp.
72. Lancaster J.E. & Alexander D.J. (1975). - Newcastle disease:
vims and spread. Monograph No. 11. Canada Department of
Agriculture, Ottawa, 79 pp.
73. Lomniczi B., Wehmann E., Herczeg J . , Ballagi-Pordany A.,
Kaleta E.F., Werner O., Meulemans G., Jorgensen P.H.,
Mante A.P., Gielkens A.L.J., Capua I. & DamoserJ. (1998). Newcastle disease outbreaks in recent years in Western
Europe were caused by an old (VI) and a novel genotype
(VII). Arch. Virol, 143, 49-64.
74. McFerran J.B. (1989). - Control of Newcastle disease in
Northern Ireland. In Proc. avian exotic disease control
seminar. Animal Health Report 2. New South Wales (NSW)
Agriculture and Fisheries, Glenfield, NSW, Australia, 16-21.
75. McFerran J.B. & McCracken R.M. (1988). - Newcastle
disease. In Newcastle disease (D.J. Alexander, ed.). Kluwer
Academic Publishers, Boston, 161-183.
76. McNulty M.S., Adair B.M., O'Loan C.J. & Allan G.M. (1988).
- Isolation of an antigenically unusual paramyxovirus type 1
from chickens. Avian Pathol, 17, 509-513.
77. Meulemans G., Gonze M., Carlier M.C., Petit P., Burny A. &
Le Long (1987). - Evaluation of the use of monoclonal
antibodies to hemagglutination and fusion glycoproteins of
Newcastle disease vims for virus identification and strain
differentiation purposes. Arch. Virol, 92, 55-62.
78. Mixson M.A. & Pearson J.E. (1992). - Velogenic neurotropic
Newcastle disease (VNND) in cormorants and commercial
turkeys, FY 1992. In Proc. 96th Annual meeting of the
United States Animal Health Association (USAHA),
31 October-6 November, Louisville, Kentucky. USAHA,
Richmond, Virginia, 357-360.
79. Nagai Y., Klenk H.-D. & Rott R. (1976). - Proteolytic
cleavage of the viral glycoproteins and its significance for the
virulence of Newcastle disease vims. Virology, 72, 494-508.
80. Nagai Y., Ogura H. & Klenk H.-D. (1976). - Studies on the
assembly of the envelope of Newcastle disease virus.
Virology, 69, 523-538.
81. Nerome K., Nakayama M., Ishida M., Fukumi H. &
Morita A. (1978). - Isolation of a new paramyxovirus from
budgerigar (Melopsittacus undulatus). J. gen. Virol, 38,
292-301.
461
82. Nishikawa F., Sugiyama T. & Suzuki K. (1977). - A new
paramyxovirus isolated from cynomolgus monkeys. Jpn. J.
med. Sci. Biol, 30, 191-204.
83. Oberdorfer A. & Werner O. (1996). - Estimation of the
pathogenicity of NDV isolates by hybridisation with
digoxigenin-tailed
oligonucleotides. In Proc. Joint
3rd annual meetings of the National Newcastle Disease and
Avian Influenza Laboratories of Countries of the European
Union, 30-31 October 1995, Brussels. Commission of the
European Communities, Brussels, 58-62.
84. Oberdorfer A. & Werner O. (1998). - Newcastle disease
vims: detection and characterization by PCR of recent
German isolates differing in pathogenicity. Avian Pathol., 27,
237-243.
85. Office International des Epizooties (OIE) (1996). Newcastle disease. In Manual of standards for diagnostic tests
and vaccines, 3rd Ed. OIE, Paris, 161-169.
86. Office International des Epizooties (OIE) (1999). - OIE
official acts. II. Resolutions adopted by the International
Committee of the OIE during the 67th General Session. Bull.
Off. int. Epiz., 111 (3), 266-267.
87. O'Reilly P.J., McCullough S., Alexander D.J. & de Burca M.
(1994). - Recent avian paramyxovirus infections on the
island of Ireland. In Proc. Commission of the European
Communities meeting on viras diseases of poultry - new and
evolving pathogens, 15-16 December 1992, Brussels.
Commission of the European Communities, Brussels, 47-63.
88. Özdemir I., Russell P.H., Collier J . , Alexander D.J. &
Manvell R.J. (1990). - Monoclonal antibodies to avian
paramyxovirus type 2. Avian Pathol, 19, 395-400.
89. Panigrahy B., Senne D.A., Pearson J.E., Mixson M.A. &
Cassidy D.R. (1993). - Occurrence of velogenic viscerotropic
Newcastle disease in pet and exotic birds in 1991. Avian Dis.,
37, 254-258.
90. Parede L. & Young P.L. (1990). - The pathogenesis of
velogenic Newcastle disease virus infection of chickens of
different ages and different levels of immunity. Avian Dis.,
34, 803-808.
91. Pearson J.E., Senne D.A., Alexander D.J., Taylor W.D.,
Peterson L.A. & Russell P.H. (1987). - Characterization of
Newcastle disease virus (avian paramyxovirus-1) isolated
from pigeons. Avian Dis., 3 1 , 105-111.
92. Pedersden K.A., Sadasiv E.C., Chang P.W. & Yates V.J.
(1990). - Detection of antibody to avian virases in human
populations. Epidemiol Inject., 104, 519-525.
93. Reeve P., Alexander D.J. & Allan W.H. (1974). - Derivation
of an isolate of low virulence from the Essex '70 strain of
Newcastle disease virus. Ve£. Rec., 94, 38-41.
94. Reid J . (1961). - The control of Newcastle disease in Great
Britain. Br. vet.J., 117, 275-288.
462
95. Rima B., Alexander D.J., Billeter M.A., Collins P.L.,
Kingsbury D.W., Lipkind M.A., Nagai Y., Orvell C ,
Pringle C.R., Rott R. & ter Meulen V. (1995). Paramyxoviridae. In Virus taxonomy. Sixth report of the
International Committee on Taxonomy of Viruses
(F.A. Murphy, C.M. Fauquet, D.H.L. Bishop, S.A. Ghabrial,
A.W. Jarvis, G.P. Martelli, M.A. Mayo & M.D. Summers,
eds). Springer-Verlag, Vienna and New York, 268-274.
96. Rott R. (1979). - Molecular basis of infectivity and
pathogenicity of myxoviruses. Arch. Virol, 59, 285-298.
97. Rott R. (1985). - In vitro Differenzierung von pathogenen
und apathogenen aviaren Influenzaviren. Berl. Münch.
tierärztl Wochenschr., 98, 37-39.
98. Rott R. & Klenk H.-D. (1988). - Molecular basis of
infectivity and pathogenicity of Newcastle disease virus. In
Newcastle disease (DJ. Alexander, ed.). Kluwer Academic
Publishers, Boston, 98-112.
99. Rweyemamu M.M., Palya V., Win T. & Sylla D. (eds) (1991).
- Newcastle disease vaccines for rural Africa. Food and
Agriculture Organization Pan-African Veterinary Vaccine
Centre, Debre Zeit, Ethiopia, 219 pp.
100. Saif Y.M., Mohan R., Ward L., Senne D.A., Panigrahy B. &
Dearth R.N. (1997). - Natural and experimental infection of
turkeys with avian paramyxovirus-7. Avian Dis., 4 1 ,
326-329.
101. Samberg Y., Horenstein K., Peleg B. '& Meroz M. (1981). Use of an oil adjuvant paramyxo Yucaipa vaccine in poultry serological response. Dev. biol Standard., 5 1 , 75-78.
102. Seal B., King D.J. & Bennett J.D. (1995). - Characterisation
of Newcastle disease virus isolates by reverse transcription
PCR coupled to direct nucleotide sequencing and
development of sequence database for pathotype prediction
and molecular epidemiological analysis. J. clin. Microbiol., 33,
2624-2630.
103. Senne D.A., Pearson J.E., Miller L.D. & Gustafson G.A.
(1983). - Vims isolations from pet birds submitted for
importation into the United States. Avian Dis., 27, 731-744.
104. Smith C.V. (1964). - Some evidence for the windborne
spread of fowl pest. Meteorol Mag., 93, 257-263.
105. Spradbrow P.B. (1987). - Newcastle disease in Australia. In
Newcastle disease in poultry: a new food pellet vaccine
(J.W. Copland, ed.). The Australian Centre for International
Agricultural Research, Canberra, 40-43.
Rev. sci. tech. Off. int. Epiz., 19
106. Spradbrow P.B. (1988). - Geographical distribution.
Newcastle disease in free-living and pet birds. In Newcastle
disease (D.J. Alexander, ed.). Kluwer Academic Publishers,
Boston, 247-255.
107. Spradbrow P.B. (1992). - Newcastle disease respite for
poultry. Shell Agric, 12, 29-31.
108. Srinivasappa G.B., Snyder D.B., Marquardt W.W. &
King D.J. (1986). - Isolation of a monoclonal antibody with
specificity for commonly employed vaccine strains of
Newcastle disease vims. Avian Dis., 3 0 , 562-567.
109. Takakuwa H , Ito T., Takada A., Okazaki K. & Kida H.
(1998). - Potentially virulent Newcastle disease viruses are
maintained in migratory waterfowl populations. Jpn. J. vet.
Res., 4 5 , 207-215.
110. Utterback W.W. & Schwartz J.H. (1973). - Epizootiology of
velogenic viscerotropic Newcastle disease in southern
California, 1971-1973. J . Am. vet. med. Assoc., 163,
1080-1088.
111. Van Eck J.H.H. (1987). - Immunity to Newcastle disease in
fowl of different breeds, primarily vaccinated with
commercial inactivated oil-emulsion vaccines: a laboratory
experiment. Vet. Q., 9, 296-303.
112. Walker J.W., Heron B.R. & Mixson M.A. (1973). - Exotic
Newcastle disease eradication program in the United States
of America. Avian Dis., 17, 486-503.
113. Westbury H.A. (1981). - Newcastle disease virus in
Australia. Aust. vet.J., 57, 292-298.
114. Wobeser G., Leighton F.A., Norman R., Myers D.J.,
Onderka D., Pybus M.J., Neufeld J.L., Fox G.A. &
Alexander D.J. (1993). - Newcastle disease in wild water
birds in western Canada. Can. vet. J., 34, 353-359..
115. Woolcock P.R., Moore J.D., McFarland M.D. & Panigrahy B.
(1996). - Isolation of paramyxovirus serotype 7 from
ostriches (Struthio camelus). Avian Dis., 4 0 , 945-949.