Pestivirus infections in ruminants other than cattle

publicité
Rev. sei. tech. Off. int. Epiz., 1990, 9 (1), 131-150.
Pestivirus infections in ruminants
other than cattle
P.F. NETTLETON *
Summary: Pestiviruses infect a wide range of domestic, captive and free-living
ruminants. Among domestic livestock, Border disease virus is a well recognised
cause of an important congenital disease of sheep in virtually all sheep-rearing
countries of the world. The clinical signs, pathogenesis, diagnosis, epidemiology
and control of this disease are described in detail. One natural outbreak of Border
disease in domestic goats has been described and there is serological and
virological evidence that pestiviruses occur widely in this species. A pestivirus
has been isolated from a farmed red deer (Cervus elaphus) and there is serological
evidence of a widespread low prevalence of infection among this new domestic
species. Pestiviruses have been associated also with outbreaks of disease among
captive ruminants in zoological collections.
Among free-living ruminants, pestiviruses have been recovered from dead
roe deer (Capreolus capreolus), fallow deer (Dama dama), African buffalo
(Syncerus caffer), giraffe (Giraffa camelopardalis) and wildebeest (Connochaetes
spp.) but in all these instances the contribution of the virus to the cause of the
disease was uncertain. Serological surveys have shown that many species of freeliving ruminants in North America, Europe and Africa have varying prevalence
rates of antibodies to pestiviruses.
KEYWORDS: Border disease - Border disease virus - Bovine virus diarrhoea
virus - Control - Deer - Epidemiology - Free-living ruminants - Goats Pathogenesis - Pestivirus - Ruminants - Sheep.
INTRODUCTION
The three pestiviruses, h o g cholera (classical swine fever) virus (HCV), bovine
virus diarrhoea (mucosal disease) virus (BVDV) and Border disease virus (BDV) were
named after t h e important diseases they cause. T h e recognition of a serological
relationship between viruses causing a systemic haemorrhagic disease of pigs, a n enteric
disease of cattle and a congenital disease of sheep remains a tribute to those responsible
(19, 53, 58).
Pestiviruses appear t o infect naturally only the even-toed ungulates belonging t o
the order Artiodactyla, within which there are 11 species of pig a n d 173 species of
ruminant (80). Despite attempts t o adapt pestiviruses t o grow in a variety of other
* Moredun Research Institute, 408 Gilmerton Road, Edinburgh EH17 7JH, Scotland, United
Kingdom.
132
hosts, only rabbits appear to support virus replication (22). Recent reports of
antibodies to pestiviruses in h u m a n sera (28, 59, 81) and pestivirus antigen in h u m a n
stools (83) require further substantiation, but raise the possibility of h u m a n infection
with a serologically related virus.
The success of pestiviruses, particularly in ruminants, is due to their ability to
cross the placenta, invade the fetus and set u p a persistent infection which continues
into post-natal life. These persistently infected animals excrete virus continuously and
spread infection wherever they go, sometimes for years (31, 49, 73).
This paper will address pestivirus infections in all ruminants, except cattle. After
a brief consideration of the relationship between ruminant pestiviruses, the main
features of Border disease (BD) in sheep will be described, followed by sections on
BD in goats a n d pestivirus infections in other farmed, captive and free-living
ruminants.
RELATIONSHIPS BETWEEN A N D AMONG
R U M I N A N T PESTIVIRUSES
Traditionally, pestiviruses isolated from pigs have been termed H C V , those from
cattle BVDV and those from sheep and goats BDV, but as new information emerges
the picture becomes more complex. Nevertheless, nearly all studies of the antigenic
relationship between representative isolates of the three pestiviruses have readily
differentiated H C V from the ruminant pestiviruses (31). The differentiation of bovine
virus diarrhoea (BVD) and BD viruses is less clear-cut. Serological comparisons of
more t h a n 110 British isolates using polyclonal and monoclonal antisera indicate the
presence of at least two antigenic groups of pestivirus, one of which predominates
in cattle and one in sheep (21, 47). There is limited information on the antigenic
relatedness between pestiviruses from other ruminants, although isolates from a giraffe
and a fallow deer have been shown to be substantially different (16), and the fallow
deer isolate is different from BVDV and BDV isolates (21).
T h e probability exists, therefore, that pestiviruses have evolved along with their
own host species. Interspecies transmission is achieved easily experimentally (31) and
it is prudent to believe that it will occur readily in domestic and free-living ruminants
when permitted to do so by new husbandry practices or changes in population
dynamics.
BORDER DISEASE OF SHEEP
Introduction
Border disease is a congenital disease of sheep first reported from the Border region
between England and Wales (33). Since then BD has been recorded in Scotland (6),
New Zealand (46), Ireland (30), Australia (1), USA (34), Switzerland (18), Greece
(66), Netherlands (68), C a n a d a (57), Norway (43), Federal Republic of Germany (41),
Syria (82), France (15) and Sweden (2). In addition, there is serological evidence that
133
BD is present in sheep in Nigeria (67) and the G e r m a n Democratic Republic (39) and
there is a strong likelihood that sheep flocks in other countries will be shown to be
infected by future investigators.
Virtually all field isolates of BDV are non-cytopathic in cell cultures, although
cytopathic strains have been described (37, 74). While the non-cytopathic biotypes
cause congenital disease and persistent infection, cytopathic isolates have been
recovered from sheep dying of a 'mucosal disease-like' syndrome (7, 27).
Review articles on BD include a m o n o g r a p h (8), a general review (70), an u p d a t e
on clinical disease (48) and chapters in two books (4, 31).
Clinical disease
One or m o r e of the following signs m a y indicate the presence of BD in a flock:
1. A n excessive number of abortions and barren ewes and the birth of small weak
lambs (Fig. 1).
FIG. 1
A group of hand-reared one-week-old lambs
affected with Border disease
All were small and only one was able to stand unaided.
At one month old, 3 of the 4 lambs were sufficiently recovered to move about freely
134
2. A number of lambs being b o r n with abnormal b o d y conformation, tremor
a n d / o r fleece changes sometimes with abnormal pigmentation (Fig. 2). T h e fleece
changes are due to long hairs rising above the fleece to form a ' h a l o ' effect especially
along the neck and back (Fig. 3). This effect is most evident in smooth-coated breeds
and is much less obvious in the coarse-fleeced breeds such as the Scottish Blackface.
Affected lambs have been termed 'hairy-shaker' or 'fuzzy lambs' in English-speaking
countries, and 'pellous' or ' b o u r r u s ' in France.
FIG.
2
Characteristic stance of a B D affected lamb
Hind legs splayed to reduce swaying of hindquarters.
Tail swinging from side to side
135
FIG. 3
Border disease lamb with hairy fleece
Long hairs rising above the rest of the fleece form a 'halo' effect,
especially over the back of the neck
3. A group of older lambs, especially a r o u n d weaning time, in which some have
died and others are scouring a n d / o r ill-thriven.
4. Occasionally other unusual clinical signs are associated with infection. In one
outbreak in France, lambs showed an unusual atrophic lesion of the diaphragm which
resulted in constriction between the thorax and a b d o m e n (64).
Pathogenesis
Infection
of non-pregnant
sheep
Infection of n o r m a l healthy sheep with virtually all BDV isolates is short-lived
and mostly sub-clinical. Mild pyrexia and transient lymphopaenia coincide with
viraemia, but with the production of neutralising antibodies 2 to 3 weeks after infection
these signs disappear.
O n e French isolate of BDV, however, has been shown t o produce profound
leucopaenia and death in 5 0 % of 3- to 5-month-old lambs. This unusually pathogenic
136
strain of BDV was recovered from a case of Syndrome ' X ' [also called Aveyron
disease, ovine leucopaenic enterocolitis or petega ovina (sheep plague)] first reported
in December 1983 in the Aveyron region of France a m o n g sheep reared intensively
for the production of milk used in the manufacture of Roquefort cheese. This new
disease killed 1,500 ewes a n d 24,000 lambs in 1984. T h e principal symptoms were
severe depression, pyrexia and diarrhoea and at post-mortem examination
haemorrhages were seen at m a n y sites and were consistently present in the caecum,
colon and mesenteric lymph nodes. Some recovered ewes later aborted or gave birth
to weak shaking lambs with p o o r viability. The incidence of the disease fell sharply
in 1985 and has remained low and although its cause was never determined
conclusively, characteristics of the syndrome suggested it had a viral aetiology. Of
t h e 5 viral agents recovered, only t h e B D virus isolate (AV2 strain) has a strong claim
for having m a d e a major contribution to causing syndrome ' X ' (17).
One other pestivirus isolate has been shown to cause disease in 4- to 5-month-old
lambs. This isolate, recovered in the Netherlands, was a pestivirus contaminant of
a live H C V vaccine. The contaminant was probably of sheep origin since its most
likely source was the secondary lamb kidney cells used to prepare the vaccine. Lambs
given the contaminated vaccine developed fever, prolonged leucopaenia, anorexia,
conjunctivitis, nasal discharge, pale conjunctivae, dyspnoea and diarrhoea and 4 of
8 lambs died (78).
Infection
of pregnant
ewes
The most serious consequences of BDV infection occur when the virus infects
susceptible ewes during pregnancy. The ewes show no clinical signs but virus spreads
rapidly t o the placenta and crosses t o the fetus within one week of infection. T h e
immune response of the ewe quickly eliminates all virus from the maternal tissues
but it has n o effect in the fetus where virus can persist.
Fetal
infection
The outcome of the fetal infection depends on the strain and dose of virus, the
breed of the fetus and its ability to repair damage but most important is the stage
of fetal development at which infection occurs. The age at which the fetus gains
immunological competence is critical in determining the distribution and persistence
of virus, which in turn influences the extent of fetal damage. The ovine fetus can
first respond to an antigenic stimulus between approximately 60 and 80 days of
gestation. T h e possible fates of fetuses before, during or after this crucial period are
summarised in Figure 4.
T h e most dangerous time for a fetus t o become infected is in the first 60 days
of gestation. Virus replication is uncontrolled and the death of the fetus is likely.
Death may occur rapidly leading to resorption or the unnoticed abortion of small
fetuses or may not occur until weeks or m o n t h s after infection when the subsequent
abortion or stillbirths are obvious. It is also possible for one fetus to die in early
gestation and be found mummified at the birth of its surviving twin. In lambs surviving
infection in early gestation virus is widespread in virtually all organs. Typically there
is n o evidence of any inflammatory reaction. T h e principal pathological findings are
myelin deficiency in the CNS which accounts for the tremor and an increase in the
number of primary hair follicles causing 'hairiness'. The low pathogenicity of some
virus strains, however, means that some lambs can be b o r n persistently infected with
virus without showing any clinical signs and with only minimal pathological
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Conception.
20
Early Gestation
40
60
Days
80
of
gestation
Onset of
|foetal immune
response
Mid Gestation
100
Late Gestation
120
140
Birth
"Hairy-Shaker",
weak or normal
PERSISTENTLY INFECTED
VIRAEMIC LAMBS
Weak or normal
or late
lambs w i t h
gestation.
antibody to B D V
Also severe
C N S defects
LAMB
STATUS
As for early
VIRUS
VIRUS
+
+
ANTIBODY
ANTIBODY
+
FIG.
VIRUS
o r _
o r _
ANTIBODY
+
4
Diagram showing the likely virological and serological status of lambs at birth
following in utero infection with BDV during early, mid or late gestation
138
lesions ( 1 4 ) . Precolostral blood samples from 'hairy-shaker' and other persistently
infected lambs contain readily detectable amounts of infectious BDV. Such lambs
are tolerant to the virus and have a persistent infection usually for life (69).
If fetal infection occurs when the i m m u n e system is beginning to develop (60-80
days) the outcome is unpredictable. Some lambs will be born viraemic and persistently
infected without detectable antibody in precolostral blood. Others will be b o r n virus
negative and antibody positive. Infection at this stage can result also in widespread
inflammatory lesions in the CNS leading to cerebral cavitation and cerebellar dysplasia;
the alternative pathology of BD (5). Lambs thus affected frequently have severe
nervous symptoms and major locomotor disturbances and have a high concentration
of serum antibody to BDV (61).
Fetal infection after 80 days gestation is met by an i m m u n e system capable of
eliminating the virus. Fetal death is rare and virtually all lambs will be born apparently
n o r m a l . They will be free of virus but have demonstrable antibody.
Persistently
infected
(PI)
lambs
Persistent infections with BDV can be established only if lambs are infected during
their first 80 days of intra-uterine life. At birth, clinically affected lambs have a low
chance of survival. M a n y die early in life while survivors have a poor growth rate
and an increased susceptibility to other diseases. Less severely affected lambs can
be reared with careful nursing but death may occur at any age. As lambs mature,
the nervous signs gradually diminish but may recur at times of stress. ' H a l o ' hairs
are soon lost from the birth-coat which is replaced by a coarse fleece. Whilst some
affected lambs grow poorly and die young, others mature normally and can survive
as persistent excretors of virus for years.
Most P I lambs will receive colostral antibody to BDV and for the first three months
of life can be serum antibody positive and viraemic. The virus can be difficult to
detect in serum during this time but can be recovered readily from leucocytes. Lambs
become seronegative as the colostral antibody concentration wanes. Virus persists
in most tissues and the lambs remain a potent source of infection.
Within groups of P I lambs some animals can suffer from chronic wasting, others
can develop excessive ocular and nasal discharges sometimes with respiratory distress,
while others develop an intractable scour and die within 2 to 4 weeks. Necropsy of
these scouring lambs often reveals gross thickening of the distal ileum, caecum and
colon resulting from focal hyperplastic enteropathy. Cytopathic BDV can be recovered
from the gut of these lambs and this syndrome has several similarities with bovine
mucosal disease (7, 27).
P I sheep surviving t o breeding age often have reduced fertility but P I ewes have
produced infected lambs in successive pregnancies (10, 79). Also virus-containing
semen from a P I r a m can produce P I offspring, with the early embryo becoming
infected from virus replicating in the uterine epithelium (26).
Diagnosis
The diagnosis of BD on clinical grounds will present little difficulty if typical 'hairyshaker' lambs are b o r n . Often however, laboratory confirmation will be necessary
since swayback, 'daft' lamb disease, bacterial meningo-encephalitis, focal symmetrical
encephalomalacia and hypothermia m a y have to be considered in the differential
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diagnosis of affected lambs. The specimens required by the laboratory to confirm
BD are summarised in Table I. As placentas and fetuses aborted due to BDV infection
have n o distinguishing characteristics, laboratory confirmation will be required to
differentiate BD from the other known infectious causes of ovine abortion. All animals
in suspected groups should be blood sampled in order to detect the antibody negative,
virus positive persistently infected sheep, whereas to determine the presence and extent
of BDV infection in a flock, 10% of animals from different age groups should be
tested for antibody. The most commonly used laboratory methods for demonstration
of virus are detection of viral antigen in cryostat sections of tissues using
immunofluorescence (IF), and virus isolation in susceptible ovine cell cultures, e.g.
fetal lamb kidney or muscle cells, with detection of the non-cytopathic virus by I F
or immunoperoxidase (IP) tests. Serum neutralisation or E L I S A methods are used
for detecting specific antibody. Histopathology on brain and spinal cord is also useful
if skilled interpretation is available.
TABLE I
Specimens to be collected for the laboratory confirmation of BD
Clinical
manifestation
Live animal
Dead animal
'Hairy-shaker' or weak
lambs; also poorly
thriving or scouring
lambs
Whole blood (clotted
and heparinised) for
virus isolation and
serology from both
the lamb and its dam
Thyroid, kidney, brain, spleen, gut
and lymph nodes: fresh for antigen
detection and in virus transport medium
for virus isolation. Heart blood for
serology. Brain and spinal cord in
calcium formol saline for
histopathology
Abortion
Blood from dam for
serology and virus
isolation
Tissues as above plus placenta for
antigen detection and virus isolation.
Brain and spinal cord in calcium
formol saline for histopathology
Epidemiology
Sheep-to-sheep contact is the principal way in which BDV is spread, and the most
potent source of virus is the persistent excretor. Bought-in P I sheep have been shown
to introduce BDV into a susceptible flock and cause a serious outbreak of B D , and
many other outbreaks of BD have a history of introduction of new stock at the
beginning of the breeding season (14, 76). M o r e intensive husbandry, particularly
housing during early pregnancy, increases the risk of an explosive outbreak of B D .
Under experimental conditions pestiviruses from other species can also cause BD
in sheep so that, among domestic animals, cattle in particular but also goats and
possibly pigs represent potential sources of infection. A m o n g free-living ruminants
pestiviruses have been isolated from red, roe and fallow deer and serological surveys
in E u r o p e , N o r t h America and Africa have shown that m a n y species have detectable
antibodies t o pestiviruses (see section below). Therefore, where sheep are grazed
extensively in contact with free-living ruminants the possibility of infection from these
other species cannot be excluded.
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One other possible source of BDV infection which cannot be ignored is a modified
live vaccine (MLV) contaminated with a pestivirus. All M L V ' s produced in ovine,
bovine or porcine cell cultures, or in medium supplemented with serum from these
species run the risk of being contaminated with a pestivirus (72). Screening techniques
must include I F or I P tests to detect non-cytopathic viruses. Both sheep pox and orf
virus vaccines administered to sheep have been incriminated as vectors of BDV
infection (41, 66).
Control
Countries importing high quality breeding stock should ensure that they originate
from flocks with no serological evidence of B D . Seronegativity of individual animals
from infected flocks is not acceptable since such sheep could be seronegative, virus
positive carriers. In countries where the disease is endemic, the introduction of
replacement breeding stock onto farms with no history of BD needs careful
consideration. Ideally, replacement females should be home-bred and purchased rams
tested to ensure they are not persistently infected. Where females are bought-in
the feasibility of testing t h e m should also be considered. Newly purchased females
should always be mated and kept separate from the rest of the flock until lambing
time.
In a flock which has recently had a sporadic outbreak of BD, the entire lamb
crop and the sheep suspected of or shown by blood tests to have introduced infection
must be removed from the farm before the start of the next breeding season. Disposal
by slaughter is the only way of preventing further spread of disease. Control of
infection in endemically infected flocks by the identification and disposal of
persistently infected sheep m a y not be practicable. In such a flock, control of disease
can be achieved by deliberately exposing all breeding stock t o k n o w n persistently
infected lambs. This natural exposure of breeding stock should be done when they
are not pregnant and at least two months before they are mated. The rate of virus
spread will depend on the ratio of P I to susceptible animals and the closeness of their
contact. Close herding indoors for at least 3 weeks is recommended for effective spread
of BDV.
It is very likely that the vaccination of female breeding stock several months before
tupping will ultimately play a major role in the control of B D . There are currently
n o vaccines available against BD and there is a need to develop one to protect sheep
against b o t h the BD virus which predominates in them and the antigenically
distinguishable viruses which have been recovered from sheep but which are more
closely related to BVD virus isolates from cattle (21, 47, 75). In the meantime, in
countries where BVDV vaccines are licensed for use in cattle, their use in sheep could
be considered. Such vaccines, however, should be critically evaluated to see if they
afford protection against local isolates of BDV.
BORDER DISEASE OF GOATS
There is serological evidence that BD occurs in goats in Africa (12, 67), North
America (25, 36), Australia (24) and E u r o p e (44). There appears to have been only
a single case of spontaneous clinical BD (44), although pestiviruses have been isolated
from aborted goat fetuses (52, 56) and the lung of a kid which died at 4 m o n t h s of
age (23).
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Experimental infections of pregnant goats with BDV produces severe placentitis
and clinical and pathological signs in the offspring similar to severe BD in sheep (9,
32, 42). Goats also appear very susceptible to H C V : intravenous inoculation of 13
pregnant goats with virulent H C V between 64 a n d 84 days of gestation resulted in
all their offspring becoming infected. Six goats kept until parturition produced 6
normal and H C V antibody positive, one apparently normal but dead, one mummified
and 3 oedematous kids (65).
PESTIVIRUS INFECTION IN F A R M E D RED DEER
The only other domestic r u m i n a n t from which a pestivirus has been recovered
is a penned red deer calf which died approximately 24 hours after first being seen
unwell. It was considered that the non-cytopathic virus was unlikely to have been
responsible for the symptoms and fatal outcome of this illness but that it may have
been a contributory factor (50).
The experimental infection of healthy red deer calves with BVD and BD viruses
results in seroconversion without obvious disease (45; Nettleton, unpublished findings).
A serological survey of 371 British farmed deer revealed 6% had antibodies to
pestiviruses (Nettleton, unpublished findings).
PESTIVIRUS INFECTION OF R U M I N A N T S
IN ZOOLOGICAL COLLECTIONS
Outbreaks of disease with similarities to mucosal disease in cattle have been
described in captive ruminants in zoological collections in the H a n o v e r Z o o and four
zoos in the U S A .
L a c k of virological c o n f i r m a t i o n m e a n s t h a t the o u t b r e a k in t h e H a n o v e r Z o o
cannot be attributed with certainty t o a pestivirus infection (35). A l t h o u g h extensive
virological a n d serological investigations were carried o u t in t h e A m e r i c a n
o u t b r e a k s , i n t e r p r e t a t i o n of t h e results w a s c o m p l i c a t e d b y t h e diagnosis of
malignant c a t a r r h a l fever ( M C F ) in s o m e of t h e a n i m a l s a n d b y a d m i n i s t r a t i o n
of B V D V vaccines t o in-contact a n i m a l s . Nevertheless, pestiviruses were isolated
from t w o wildebeest (Connochaetes
s p p . ) , a nilgai {Bosalephus
tragocamelus),
an axis deer (Cervus axis) a b a r a s i n g h a deer (Cervus duvauceli),
muntjac
{Muntiacus reevesi), serow (Capricornis sumatraensis),
p i g m y goats (Capra hirus)
and a Waterhuck (Kobus ellipsiprymnus).
T h e r e w a s also serological evidence of
pestivirus infection in 49 species of r u m i n a n t b u t m a n y of these h a d been vaccinated
(20). T h e species with a n t i b o d i e s a p p a r e n t l y d u e t o n a t u r a l infection a r e included
in T a b l e I I .
Veterinarians in charge of valuable zoological collections should be aware of the
dangers of pestivirus infection in r u m i n a n t s , and the possibility of enhanced
pathogenicity of isolates crossing species barriers. A policy of quarantine and testing
to prevent the introduction of P I animals should be followed.
142
TABLE II
Captive or free-living ruminants with evidence of pestivirus infection
Continent
[Captive (C) or
free-living (FL)]
Species
Evidence for infection
Antibody (AB) or
virus isolation (VI)
Reference
Camelidae
Dromedary
(Camelus dromedarius)
Llama (Lama guanicoe)
America (C)
America (C)
AB
AB
20
20
America (C)
VI
20
America (C)
VI
20
Europe (FL)
Europe (FL)
Australasia (FL)
America (FL)
AB
38
VI/AB
AB
AB
21,38,40,51,78
35, 64
72
America (FL)
AB
35
America (C)
VI
20
Europe (FL)
AB
13, 38, 40, 45
Europe (FL)
VI/AB
3, 40, 63
Europe (FL)
AB
38
America (FL)
Australasia (?)
AB
VI
35
64
Africa (C)
Africa (FL)
VI
AB
59
29, 35
America (C/FL)
AB
11, 20
Africa (FL)
America (C)
AB
AB
29, 35, 59
20
AB
AB
29
20
VI
20
AB
29
Cervidae
Axis deer (Cervus axis)
Barasingha deer
(Cervus duvauceli)
Chinese water deer
(Hydropotes inermis)
Fallow deer (Dama dama)
Moose (Alces alces)
Mule deer
(Odocoileus hemionus)
Muntjac
(Muntiacus reevesi)
Red deer
(Cervus elaphus)
Roe deer
(Capreolus capreolus)
Sika deer
(Cervus nippon)
White-tailed deer
(Odocoileus virginianus)
Deer -
unspecified
Giraffidae
Giraffe
(Giraffa camelopardalis)
Antilocapridae
Pronghorn antelope
(Antilocapra americana)
Bovidae
Eland
(Taurotragus spp.)
Kudu
(Tragelaphus strepsiceros) Africa (FL)
America (C)
Nilgai
(Boselaphus tragocamelus) America (C)
Nyala
(Tragelaphus angasi)
Africa (FL)
143
TABLE II (contd.)
Species
Continent
[Captive (C) or
free-living (FL)]
Evidence for infection
Antibody (AB) or
virus isolation (VI)
Reference
Oryx/gemsbok
(Oryx gazella)
Africa (FL)
America (C)
AB
AB
29
20
Africa (FL)
AB
29
Africa (FL)
AB
29
Africa (FL)
America (C)
AB
VI/AB
29
20
Africa (FL)
AB
29
Africa (FL)
AB
29, 61
Africa (FL)
AB
29, 61
Africa (FL)
AB
29
America (C)
AB
20
Africa (FL)
America (C)
VI/AB
VI/AB
29, 55
20
Africa (FL)
AB
29
Africa (FL)
AB
61
Africa (FL)
America (C)
AB
AB
29
20
Africa (FL)
America (C)
AB
AB
29
20
(Capra aegagrus aegagrus) America (C)
Europe (FL)
Ibex (Capra ibex)
Pygmy goat (Capra hircus) America (C)
AB
AB
VI
20
3
20
Europe (FL)
AB
3
(Capricornis sumatraensis) America (C)
America (C)
Urial (Ovis vignei)
VI
AB
20
20
America (FL)
AB
54
America (C)
AB
20
America (C)
AB
20
Africa (FL)
VI/AB
29, 59
America (C)
AB
20
Sable antelope
(Hippotragus niger)
Defassa Waterhuck
(Kobus defassa)
Waterhuck
(Kobus ellipsiprymnus)
Lechwe
(Kobus leche)
Reedbuck
(Redunca arundinum)
Hartebeest
(Alcelaphus buselaphus)
Tsessebe
(Damaliscus lunatus)
Bontebok/blesbok
(Damaliscus dorcas)
Wildebeest
(Connochaetes spp.)
Impala
(Aepyceros melampus)
Korin/red-fronted gazelle
(Gazella rufifrons)
Springbuck
(Antidorcas marsupialis)
Duiker
(Sylvicapra grimmia)
Dik-dik (Madoqua kirki)
Bezoar
Chamois
(Rupicapra rupicapra)
Serow
American bighorn
(Ovis canadensis)
Barbary sheep/Aoudad
(Ammotragus lervia)
Mountain goat
(Oreamnos americanus)
African buffalo
(Syncerus caffer)
Gaur
(Bos gaurus)
144
PESTIVIRUS INFECTION OF FREE-LIVING RUMINANTS
Pestiviruses have been recovered from dead roe deer (Capreolus capreolus) (62), fallow
deer (Dama dama) (77), African buffalo (Syncerus coffer), giraffe
(Giraffa
camelopardalis) (29, citing W . Plowright) and wildebeest (Connochaetes spp.) (55). The
role of the viruses in causing diseases in these free-living ruminants is uncertain. Similar
uncertainty relates to outbreaks of disease resembling mucosal disease in white-tailed
deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus) in the U S A (35).
Serological surveys have revealed t h e presence of antibodies to pestiviruses in the
sera of several species of free-living ruminants (Table II). In E u r o p e , low
seroprevalence rates of 5 t o 1 0 % have been detected in red deer (Cervus
elaphus),
sika deer (C. nippon), roe deer (Capreolus capreolus), fallow deer (Dama dama),
chamois (Rupicapra rupicapra) and ibex (Capra ibex) (3, 38, 40). In N o r t h America,
antibody to B V D virus has been demonstrated in white-tailed a n d mule deer,
p r o n g h o r n antelope (Antilocapra americana) a n d moose (Alces alces) (35, 71).
A n outstanding study on 3,359 sera from ruminants a n d other species in nine
African countries by H a m b l i n a n d Hedger (29) detected antibody t o BVDV (NADL
strain) in 17 of 29 species of ruminants. Seroprevalence rates of between 30 a n d 87%
were detected in African buffalo, kudu (Tragelaphus strepsiceros), eland (Taurotragus
oryx),
Waterhuck, defassa Waterbuck (Kobus
defassa),
reedbuck
(Redunca
arundinum),
sable antelope (Hippotragus
niger) a n d oryx (Oryx gazella). It is
reasonable t o believe that disease due t o pestiviruses is occurring in these 8 species
at least, since seroprevalence rates of this order are associated with a widespread low
incidence of disease in sheep a n d cattle. It is also reasonable t o suppose that many
other species of ruminants h a r b o u r pestiviruses.
CONCLUSION
A m o n g ruminants other than cattle, pestiviruses are known to be serious pathogens
of sheep in which they cause B D . Studies on this important congenital disease have
helped t o demonstrate the pivotal role of fetal infection in pestivirus infections.
Of t h e other domestic ruminants, goats are very susceptible t o experimental
infections with pestiviruses b u t natural disease is rare and although pestiviruses have
been isolated from red deer there is no evidence that they cause disease in this species.
Similarly, the role of pestiviruses in other ruminant populations is largely unknown
although there is some evidence that they m a y be significant: infection has been
demonstrated serologically in more t h a n forty species. Outbreaks of disease similar
to those caused by pestiviruses in domestic ruminants have been described in captive
and free-living ruminants, with pestiviruses being isolated from some such cases.
The elucidation of t h e epidemiology of pestiviruses in free-living ruminants and
the antigenic relationship of isolates from various species would make an important
contribution t o further understanding of the biology of these fascinating viruses.
*
* *
145
LES INFECTIONS PROVOQUÉES PAR LES PESTIVIRUS CHEZ LES RUMINANTS
AUTRES QUE LES BOVINS. - P.F. Nettleton.
Résumé: Les pestivirus peuvent infecter un grand nombre de ruminants,
domestiques, vivant en captivité ou en liberté. Le virus de la maladie de la
frontière (border disease) est responsable d'une maladie congénitale dont
l'importance est bien connue. On l'observe pratiquement dans tous les pays
d'élevage ovin. L'auteur expose en détail les signes cliniques, la pathogenèse,
le diagnostic, l'épidémiologie et la prophylaxie de cette maladie. On a décrit
un foyer de maladie de la frontière apparu dans les conditions naturelles chez
des chèvres domestiques. On a également la preuve sérologique et virologique
de la fréquence des pestivirus dans cette espèce. Un pestivirus a été isolé chez
un cerf d'élevage (Cervus elaphus) et on a la preuve sérologique que l'infection
se rencontre chez cette nouvelle espèce domestique, dans de nombreux pays,
avec une faible prévalence. Les pestivirus ont aussi été responsables de foyers
de maladie chez des ruminants en captivité dans des jardins zoologiques.
Parmi les ruminants vivant en liberté, des pestivirus ont été identifiés chez
le chevreuil européen (Capreolus capreolus), le daim (Dama dama), le buffle
(Syncerus caffer), la girafe (Giraffa camelopardalis) et le gnou (Connochaetes
spp.), mais dans aucun de ces cas la responsabilité du virus dans le développement
de la maladie n'a été établie avec certitude. Des enquêtes sérologiques ont montré
que beaucoup d'espèces de ruminants, vivant en liberté en Amérique du Nord,
en Europe et en Afrique, présentent des anticorps dirigés contre les pestivirus,
avec une prévalence variable.
MOTS-CLÉS : Cerfs - Chèvres - Epidémiologie - Maladie de la frontière Moutons - Pathogenèse - Pestivirus - Prophylaxie - Ruminants - Ruminants
vivant en liberté - Virus de la diarrhée virale bovine - Virus de la maladie de
la frontière.
*
* *
LAS INFECCIONES PROVOCADAS POR PESTIVIRUS EN RUMIANTES DISTINTOS
DE LOS BÓVIDOS. - P.F. Nettleton.
Resumen: Los pestivirus pueden infectar gran cantidad de rumiantes, tanto
domésticos como en cautividad o en libertad. El virus de la enfermedad de la
frontera (border disease) es responsable de una enfermedad congénita cuya
importancia es bien conocida. Se lo observa en prácticamente todos los países
de explotación ganadera ovina. El autor expone detalladamente los síntomas
clínicos, la patogénesis, el diagnóstico, la epidemiología y la profilaxis de esta
enfermedad. Se ha descrito un foco de enfermedad de la frontera que apareció
en cabras domésticas en condiciones naturales. Se cuenta asimismo con las
pruebas serológica y virológica que confirman la frecuencia de pestivirus en
esta especie. Un pestivirus fue aislado en un ciervo de cría (Cervus elaphus)
y se tiene la prueba serológica de que la infección puede hallarse en esta nueva
especie doméstica, en varios países, con baja prevalencia. Los pestivirus han
sido también causa de focos de enfermedad en rumiantes cautivos en jardines
zoológicos.
Entre los rumiantes en libertad, se identificaron pestivirus en el corzo europeo
(Capreolus capreolus), el gamo (Dama dama), el búfalo de Africa (Syncerus
caffer), la jirafa (Giraffa camelopardalis) y el ñu (Connochaetes spp.), pero
en ninguno de estos casos se pudo establecer con certeza la responsabilidad del
146
virus en el desarrollo de la enfermedad. Investigaciones serológicas mostraron
que muchas especies de rumiantes que viven en libertad en América del Norte,
Europa y Africa presentan anticuerpos contra los pestivirus, con una prevalencia
variable.
P A L A B R A S C L A V E : Cabra - Ciervo - Enfermedad de la frontera Epidemiología - Ovinos - Patogénesis - Pestivirus - Profilaxis - Rumiantes Rumiantes en libertad - Virus de la diarrea viral bovina - Virus de la enfermedad
de la frontera.
*
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