products Animal health risks associated with ostrich F.W. Huchzermeyer

Rev. sci. tech. Off. int. Epiz., 16 (1 ), 111-116
Animal health risks associated with ostrich
products
F.W. Huchzermeyer
Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort 0110, South Africa
Summary
Five diseases recorded in ostriches are regarded as posing a potential animal
health threat to meat-importing countries. Newcastle disease causes an
atypically low mortality in ostriches: infected birds display typical nervous
symptoms but no pathognomonic lesions which could be detected during
post-mortem inspection. The vaccination of feedlot birds and a thorough
ante-mortem examination are regarded as necessary precautions to ensure virus
carriers are not among those animals destined for slaughter and subsequent
export.
Avian influenza produces clinical depression and lesions can be detected at
post-mortem examination. Borna disease appears to affect mainly younger birds,
and the virus is probably not present in the meat of affected birds. Finally, there is
little evidence to suggest that ostriches could play a role in the epidemiology of
transmissible spongiform encephalopathies. Cases of anthrax are extremely rare.
The importation of deboned ostrich meat reduces the risk of infected scraps being
fed to susceptible animals.
Keywords
Anthrax - Avian influenza -
Borna disease -
Newcastle disease - Ostriches
-
Transmissible spongiform encephalopathy.
Introduction
Newcastle disease
In recent years, there has been a rapid, world-wide expansion
of ostrich production. Large quantities of ostrich meat are
exported by a number of producing countries, chiefly South
Africa, Israel, Zimbabwe, Namibia and the United States of
America (USA). Other countries are rapidly approaching the
slaughter and exporting stage in the development of their own
ostrich industries. Consequently, there is - from an animal
health point of view - growing concern about the safety of
ostrich products for importing countries.
Newcastle disease (ND) is a highly contagious viral infection
which affects domestic poultry in particular. There are many
different strains of the ND virus: these are indistinguishable
serologically, but vary in their virulence, pathogenicity,
infectivity and to a certain extent, their host range.
Ostriches do not have any specific viral or bacterial infections
of their own, but are susceptible to a number of infectious
agents of other avian and mammalian species. This paper
reviews the current literature on the occurrence of Newcastle
disease, avian influenza, Borna disease, transmissible
spongiform encephalopathies and anthrax in farmed
ostriches, all of which could pose a threat to animal industries
in importing countries.
According to their virulence, the strains are classified as
lentogenic (of low virulence), mesogenic (of moderate
virulence) and velogenic (of high virulence). Lentogenic f i e l d
virus is of little concern, except as a source of antibodies in
exposed birds, and while mesogenic virus is readily controlled
by normal vaccination practices as used in the poultry
industries of many countries, outbreaks of velogenic ND can
cause severe losses in affected poultry flocks regardless of the
vaccination measures taken.
Some countries have successfully eliminated the velogenic ND
virus and even mesogenic viruses, obviating the need to
vaccinate against ND. In other countries, however,
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particularly in Africa, South America and tropical Asia,
velogenic ND still is endemic, predominantly in backyard or
village poultry, and from time to time major outbreaks of the
disease occur. The perpetuation of velogenic ND virus in
backyard poultry flocks depends on a number of factors, such
as the absence or use of night quarters, and the separation of
brooding and rearing hens (8).
While all birds are considered susceptible to ND virus
infection - and the virus has been isolated from many wild
species - few cases of clinical disease or mortality have been
reported from birds in the wild. Members of the following
avian families have been identified as carriers or reservoirs of
ND virus: Anseriformes (waterfowl), Psittaciformes (parrots),
Passeriformes
(songbirds),
Strigiformes
(owls)
and
Falconiformes (diurnal birds of prey) ( 2 5 ) .
From time to time, cases of ND in ostriches have been
reported from zoological gardens (7, 12, 14, 1 9 ) , and these
cases have been reviewed (9, 11). Outbreaks of ND with
chronic nervous symptoms were seen in Israel in farmed
ostriches reared in close proximity to commercial poultry
(21).
In 1 9 9 3 , an outbreak of ND occurred in poultry in South
Africa and spread to ostriches (2, 10, 1 1 , 2 5 ) : the disease is
still present four years later. The pathogenicity of ostrich
isolates from South Africa and Botswana (intracerebral
pathogenicity index in specific pathogen-free chicks) was
similar to that of poultry isolates from the same area, while
ostrich isolates from Zimbabwe were indistinguishable from
lentogenic poultry vaccine strains (17). Thus, it appears that
commercial and village poultry flocks in the vicinity of ostrich
farms act as main reservoirs of the ND virus and as the source
of infection, although the role of wild birds in the
dissemination of ND, particularly to ostrich feedlots, cannot
be excluded.
From observations of field and experimental cases made by
the author, it appears that, in ostriches, the route of infection
has a major impact on the clinical manifestation of the disease.
If ostriches are kept indoors and are exposed to infection via
the respiratory route, severe respiratory disease with rapid
spread and high mortality may result, while ostriches kept in
outdoor runs usually contract the disease by the oral route,
with resulting nervous symptoms and a very slow spread of
infection. The nervous symptoms are very specific, and
appear in a progression from slight head shaking and head
scratching to the complete loss of control of neck movements
and total ataxia (10). However, there are no pathognomonic
pathological or histopathological lesions. Consequently,
diagnosis can be confirmed by virus isolation only (10, 2 1 ) .
For effective control of the disease in ostriches, it is necessary
to vaccinate all poultry within a certain radius around ostrich
farms, to disallow the keeping of any susceptible non-ratite
birds on ostrich farms, and to vaccinate all ostriches following
Rev. sci tech. Off. int. Epiz., 16(1)
a strict schedule. Preliminary trials conducted by the author
indicate that the virus does not persist in the muscles of
immunised infected birds after the initial viraemic stage.
Therefore, the vaccination of feedlot ostriches at least one
month before slaughter with approved vaccines (e.g., a
combination of live and killed emulsified vaccines) is deemed
sufficient to eliminate the danger of ND virus being exported
in the meat obtained from these birds.
A pre-slaughter inspection for the absence of the typical - or
any - nervous symptoms is another important requirement
for preventing the slaughter and subsequent export of meat
from ostriches with clinical ND.
Avian influenza
Avian influenza (AI) is a highly contagious infection which
occurs mainly in wild birds, particularly waterfowl. There are
fourteen serologically different subtypes and, in addition,
there are differences in infectivity and pathogenicity to
different bird species. The various subtypes of the AI virus are
based on antigenic differences in the haemagglutinin (H)
protein (17). Isolates of AI virus which are highly pathogenic
to poultry have always belonged to the H5 and H7 subtypes
(17).
Outbreaks of AI occurred in ostriches in South Africa in 1 9 9 2
and subsequent years ( 1 , 2, 3 ) . The virus has also been
isolated from ostriches in Zimbabwe ( 1 7 ) , and from other
ratites in the Netherlands ( 1 7 ) and the USA (18).
The subtypes isolated from ostriches in South Africa were:
H5N9, H7N1 and H9N2; from Zimbabwe: H5N2; and from
other ratites in the Netherlands: H5N9 (17); and in the USA:
H5N2 and H7N1 ( 1 8 ) . None of the ratite AI virus isolates
from South Africa, Zimbabwe or the Netherlands were
pathogenic for chickens (intravenous pathogenicity index
0.00). It is believed that the ostriches contracted the infection
from wild bird reservoirs (17).
Clinical symptoms seen in ostriches aged between 5 days and
14 months varied in that the younger birds were more
severely affected. Symptoms included green discolouration of
the urine, ruffled feathers and, in cases of secondary bacterial
infections, airsacculitis and ocular discharge were observed.
Birds over eight months of age often showed only a green
discolouration of the urine and a slight depression, and
usually recovered within two to three weeks ( 1 , 3 ) .
Post-mortem lesions were influenced by concurrent bacterial
infections. Most commonly observed were focal areas of
necrosis in the livers, a severe congestion of the proximal
small intestine with mucous contents, and pale kidneys which
excreted a greenish urine (1).
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Rev. sci tech. Off. int. Epiz., 16(1)
Vaccination with strain-specific killed vaccines did suppress
clinical disease and mortality, but did not prevent the
shedding of the virus (1).
Ante-mortem inspection of slaughter birds aimed at
preventing depressed ostriches from being slaughtered, a
reliable post-mortem inspection, and strict quarantine
measures for farms in a known outbreak, should suffice to
prevent the slaughter of viraemic birds and the possible
export of their meat.
Borna disease
Borna disease (BD) is a viral infection which can affect several
species of livestock. In 1 9 9 3 , a paretic condition was seen in
ostriches in Israel (26), which subsequentiy was diagnosed as
being associated with or caused by the BD virus (4, 5, 6, 15,
16, 27).
Ostrich chicks aged between 14 and 4 2 days were most
susceptible to disease. Sometimes incoordination was seen a
few days before the onset of paresis, from which only 1%
recovered if submitted to intensive care treatment. On affected
farms, the disease is a significant cause of mortality (16).
There were no gross post-mortem lesions. Histopathologically, there were lesions in the lumbosacral region of the
spinal cord consisting of neuron degeneration in the central
grey matter, accompanied by satellitosis and neuronophagia
(16).
On threatened farms, further outbreaks were prevented by
prophylactic injection of reconvalescent serum (4, 16, 2 6 ) .
The questions of a carrier state in ostriches and of virus
replication sites outside the nervous tissue have not yet been
addressed. However, it is unlikely that the BD virus could be
transmitted through the meat of slaughtered ostriches. The
disease has not yet been found in ostriches in any other
country.
Transmissible spongiform
encephalopathies
Transmissible spongiform encephalopathies (TSEs) have been
reported from a number of mammalian species, and in recent
years bovine spongiform encephalopathy (BSE) has become
prominent. Through the feeding of contaminated carcass meal
and of raw meat from emergency-slaughtered cattle, the
condition appears to have spread to a large number of captive
herbivorous and carnivorous wild mammal species (13).
Three ostriches from two zoos in Germany, which were
slaughtered following the detection of protracted central
nervous symptoms with ataxia, were found to present
histopathological lesions suggestive of TSEs (22, 2 3 ) . These
cases occurred in 1 9 8 6 , 1 9 8 8 and 1 9 8 9 . Reports that the
birds had received commercial rations containing carcass
meal and had also been fed meat from emergency-slaughtered
cattle were made, although it is most unlikely that ostriches
should be fed or should eat meat. However, the brain material
of these birds was not examined for the scrapie-associated
fibrils.
While scrapie-associated TSEs have not yet been reported
from any other avian species, the longer life-span of ostriches
could allow these birds to survive long enough for the disease
to manifest itself clinically. The first of the reported cases
occurred at a time when Germany was officially free from BSE
cases. There is also reason to doubt the statement that the
birds had been fed meat. However, the possibility that
transmissible TSEs could and did infect ostriches cannot be
dismissed entirely and, consequently, slaughter offal and
carcass meal from ostriches in countries with endemic BSE
should be processed accordingly, to prevent the spread of the
agent through this material.
Anthrax
Cases of anthrax have been reported from ostriches ( 2 0 , 2 4 ) .
The normal picture is that of peracute deaths with typical
post-mortem lesions. In this form, the bacteria are present in
the blood and can be demonstrated in stained blood smears.
However, there is also a mild form referred to as 'anthrax
fever' with somnolence and anorexia, from which some birds
may recover after a few days ( 2 4 ) . No cases of anthrax in
ostriches have been reported in recent years. Ante-mortem
inspection will prevent clinically depressed birds from being
slaughtered and will eliminate the danger of infected ostriches
entering the food chain.
Risks of disease transmission
through ostrich products
Deboned meat
Ostrich bone marrow is much more likely than muscle tissue
to harbour any of the viruses of the conditions described
above. Therefore, the exclusive importation of deboned
ostrich meat must be regarded as a further general measure to
reduce the risk of introducing any of these diseases. Also, the
deboned ostrich meat contains very few parts which could be
discarded and fed to susceptible animals (fowls) in the
backyard.
Dried meat
Dried meat (biltong) has the same properties as raw meat and
carries the same dangers.
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Rev. sci tech. Off. int. Epiz., 16(1)
Processed meat
Egg shells
Heat processing sterilises the meat. Heat-processed meat
products are therefore safe from an animal health point of
view, except with regard to TSE agents (prions) which are
resistant to heat sterilisation.
The shells of ostrich eggs could become infected secondarily
with ND, AI and BD viruses. However, heat sterilisation or
fumigation with formalin should suffice to render cleaned
ostrich egg shells safe.
Feathers
Eggs
There is no evidence that any of the five diseases discussed
above could be transmitted through the egg, nor have any of
the egg-transmitted Salmonella serovars been reported from
ostriches. There are, however, indications that ostriches can
be infected with poultry mycoplasmas, and these in turn
could be transmitted transovarially.
Untreated ostrich feathers could carry ND, AI or BD viruses.
Hot washing or fumigation should eliminate such a threat.
Skins
Raw and salted ostrich skins could also carry the above
viruses, while tanned skins are rendered sterile by the tanning
process.
Risques zoosanitaires liés aux produits à base d'autruche
F.W. Huchzermeyer
Résumé
Cinq maladies affectant les autruches constituent une menace zoosanitaire
potentielle pour les pays importateurs de viande. La maladie de Newcastle
entraîne chez les autruches une mortalité atypique peu élevée ; les symptômes
nerveux observés sont caractéristiques chez les individus atteints, mais
l'inspection post-mortem ne révèle aucune lésion pathognomonique. La
vaccination des autruches destinées à la consommation humaine et un examen
ante-mortem approfondi sont des précautions indispensables pour s'assurer qu'il
n'y a pas de porteurs du virus parmi les autruches destinées à l'exportation de
viande.
L'influenza aviaire se traduit par une grave atteinte clinique et par des lésions
visibles lors de l'inspection post-mortem. La maladie de Borna semble affecter
essentiellement les jeunes autruches et le virus n'est probablement plus présent
dans la viande provenant des animaux atteints. Enfin, il y a peu de preuves que les
autruches puissent jouer un rôle dans l'épidémiologie des encéphalopathies
spongiformes transmissibles. Les cas de fièvre charbonneuse sont extrêmement
rares.
L'importation de viande désossée d'autruche réduit le risque de faire consommer
à des animaux sensibles des déchets de viande infectés.
Mots-clés
Autruches - Encéphalopathy spongiforme transmissible - Fièvre charbonneuse
Influenza aviaire - Maladie de Borna - Maladie de Newcastle.
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Rev. sci tech. Off. int. Epiz., 16(1)
Riesgos zoosanitarios asociados a productos derivados de avestruz
F.W. Huchzermeyer
Resumen
Cinco son las enfermedades del avestruz que se consideran una potencial
amenaza zoosanitaria para los países importadores de carne. La enfermedad de
Newcastle causa en los avestruces una tasa de mortalidad atípicamente baja: las
aves infectadas exhiben síntomas nerviosos característicos, pero en cambio no
presentan lesiones patognomónicas visibles durante la inspección postmortem.
Para garantizar la ausencia de portadores del virus entre los avestruces
destinados a la exportación de carne, se estima necesario vacunarlos en la
granja y someterlos a una cuidadosa inspección antemortem.
La influenza aviar induce depresión clínica y causa lesiones que se pueden
detectar durante la inspección postmortem. La enfermedad de Borna parece
afectar básicamente a los avestruces jóvenes, y es probable que el virus no
permanezca en la carne obtenida a partir de casos infectados. Existen pocos
indicios, por último, de que los avestruces desempeñen un papel en la
epidemiología de las encefalopatías espongiformes transmisibles. Casos de
carbunco bacteridiano no ocurren sino muy excepcionalmente.
La importación de carnes deshuesadas de avestruz reduce el riesgo de
suministrar restos infectados de comida a animales receptivos.
Palabras clave
Avestruces - Carbunco bacteridiano - Encefalopatía espongiforme transmisible
Enfermedad de Borna - Enfermedad de Newcastle - Influenza aviar.
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•
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