D9120.PDF

Rev. sci. tech. Off. int. Epiz., 16 (1), 104-110
Animal health risks associated with
the transportation and utilisation
of wildlife products
R.G. Bengis
Chief State Veterinarian, Kruger National Park, P.O. Box 12,1350 Skukuza, South Africa
Summary
The animal health risks associated with the movement of wildlife products are
infinitely less than those associated with the movement of live animals. Very f e w
pathogens are sufficiently robust to survive the significant changes in
temperature, pH, moisture content and osmolality which occur post mortem, or
which are associated with preservation processes such as pickling, smoking or
drying. Certain pathogens, however, (e.g. foot and mouth disease, classical swine
fever [hog cholera] and African swine fever viruses and the anthrax bacillus) are
hardy and resistant to these environmental changes and therefore constitute a
finite animal health risk if raw, undercooked or under-preserved products from
infected wild animals are imported.
Other less robust pathogens, such as rinderpest virus, may remain infectious in
animal products if these are obtained from acutely infected animals and frozen
immediately.
Macroparasitic
diseases
such
as trichinellosis and
echinococcosis-hydatidosis, if present in the unprocessed tissues of infected
wildlife, are potentially infectious to carnivorous or omnivorous companion
animals. The importation of untreated w e t hides may result in the introduction of
alien ectoparasites and/or the infectious diseases for which they are vectors.
The author discusses the more significant pathogens found in free-ranging
wildlife which should be taken into consideration when importing wildlife
products from endemically or epidemically infected countries.
Keywords
Animal health - Animal products - International trade - Pathogens - Risk - Wildlife.
Introduction
The animal health risk associated with moving infected wild
animals is generally far greater than that associated with
moving wildlife products. Thus, with international movement
of wildlife products there are only a few 'foreign animal
diseases' for which a definite risk exists and for which
prevention strategies are important, if these wildlife products
are imported from a disease-endemic region of the exporting
country. The pathogens involved are usually fairly hardy and
are resistant to environmental extremes of temperature, pH,
moisture content, ultra-violet irradiation and osmolality.
Viral diseases
Foot and mouth disease
Foot and mouth disease (FMD) can potentially infect all
cloven-hoofed wild ungulates. In most countries, infected
cattle are the major source of FMD outbreaks in wildlife. On
the African continent, however, African buffalo (Syncerus
caffer) have been shown to develop long-term persistent
infection, ( 7 , 1 5 ) making them an ideal maintenance host and
reservoir for these apthoviruses. In free-ranging African
ecosystems, the endemic FMD infection in buffalo herds may,
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Rev. sci tech. Off. int. Epiz., 16 (1)
from time to time, 'spill over' into other associated clovenhoofed species and may result in short-term epizootic cycles
(3). Such epizootics, because of the difficulty in determining
their spatial and temporal scale, represent the periods of
greatest animal health risk for the movement of wildlife
products.
The decrease in pH which occurs during the glycolytic
ripening process inactivates most FMD viruses present in
skeletel muscle within 4 8 hours ( 9 ) . However, when impala
(Aepyceros melampus) were experimentally infected with a
Southern African Territories (SAT) type 1 virus strain
(SAR 9/81), this specific virus was found to be highly
myotropic in the species (virus titres > log 5 T C I D were
isolated from some muscles). Significant titres of virus were
still present in certain muscle samples after 72 hours, by
which time the pH had decreased to (and eventually stabilised
at) 5.6 (Van der Walt and Bengis, personal communication).
These findings demonstrate the risks of extrapolating from
one species to another. Furthermore, the survival of FMD
viruses at 4°C in tissues other than skeletal muscles, in which
little or no post-mortem acidification occurs, is highly
significant. Henderson and Brooksby reported virus survival
in excess of 5 months in bovine liver, rumen and lymph node
stored at 4°C ( 1 6 ) . Cottral reported virus survival for 120 days
in chilled lymph nodes (8).
5 0
Heat also inactivates the FMD virus, and 69°C appears to be
the critical temperature, although higher temperatures may be
required if the virus is protected by lipid structures, as found
in tissue cells and milk (18). Freezing preserves the virus, thus
rapidly frozen or chilled products from infected animals are
most likely to remain infectious. Pickling in brine or salting
does not destroy the virus unless vinegar or some other
organic acid is also used in the process.
The raw or partially processed organs of infected wild
ungulates are therefore potentially infectious, and appropriate
animal health preventive measures should be taken to avoid
importation or spread of the disease.
These measures should include the following:
a) Prohibit the importation of raw or unprocessed wildlife
products from any region in which FMD is endemic in the
buffalo population, or in which there is an active (buffalo- or
cattle-associated) FMD epidemic.
b) Avoid including wildlife-derived trimmings and off-cuts in
swill fed to pigs.
and viscera; such carcasses should be ripened for 4 8 hours in
a chilled hanging position, before transport.
e) Process hides of potentially infected wild ungulates using
salt plus an organic acid (e.g. citric or formic acid) or alkali
(sodium carbonate).
f) Clean skulls of potentially infected wild ungulates of all soft
tissues, and then either boil in water for 4 5 minutes or
immerse in 5% formaldehyde for 2 4 hours.
African swine fever
The natural sylvatic hosts of African swine fever (ASF)-viruses
are certain argasid ticks of the genus Omiihodoros. The ticks
are true maintenance hosts in which these viruses can cycle
independently - requiring no additional vertebrate or
invertebrate host - and both horizontal (sexual) and vertical
(transovarial) transmission have been documented ( 2 1 , 2 2 ) .
ASF can also infect wild and domestic swine, hence its
veterinary importance. ASF virus has been isolated from
warthogs
(Phacochoerus
aethiopicus),
bush
pigs
(Potamochoerus porcus) and the giant forest hog (Hylochoerus
meinertzhageni).
These infections are generally subclinical,
but virus might be present in normal physiological secretions
and excretions, and has been shown to be transmitted under
experimental
conditions
(E.C. Anderson,
personal
communication). No horizontal transmission has been
demonstrated in these wild porcine species, which appear to
be 'dead end' hosts in the absence of the argasid tick (tampan)
vectors. In contrast, ASF in domestic pigs is usually a clinical
entity with high morbidity and variable mortality. Acute
disease with high mortality is usually seen in commercial
breeds raised in intensive farming conditions, whereas
subacute and chronic disease, which may become endemic, is
more common in free-ranging rustic pigs. Horizontal
transmission readily occurs amongst domestic pigs since virus
is present in most physiological secretions and excretions and,
in the endemic free-ranging situation, these pigs may become
maintenance hosts.
The environmental stability of the ASF virus is a notable
feature. The virus has been found to survive in serum at room
temperature for 18 months (19), and in refrigerated blood for
at least six years ( 1 1 ) . The virus is still infectious after 15
weeks in chilled meat, and for three to six months in
processed hams, salamis and smoked sausages (17), Heating
at 56°C for 3 0 minutes does not kill the virus, which remains
stable at pH 4 - 1 0 . Putrefaction does not destroy the virus
quickly, which is resistant to proteases.
c) Ensure the processing of carcasses of ungulates from zones
in which FMD is endemic among wildlife by 'hot' canning
(retort cooking), hot smoking for at least 3 6 hours or pickling
of thin strips in brine containing an organic acid which
reduces the pH of the solution to below 4 . 0 , for 2 4 hours,
followed by drying to less than 4 0 % moisture content.
In wild swine, viraemia develops following exposure to an
infected tampan, and this may last three weeks. Thereafter the
virus persists in the peripheral and visceral lymph nodes for
many months (23). In turn, non-infected tampans feeding on
viraemic pigs also become infected with ASF virus.
d) Transport the carcasses of wild ungulates from adjoining,
non-endemic surveillance zones without hides, heads, hooves
In the past, ASF was limited to those parts of the African
continent corresponding to the geographic distribution of the
106
argasid tick maintenance host. During the past forty years,
however, ASF outbreaks have occurred for the first time
outside Africa: initially in Portugal, from where the disease
spread to Spain, France, Italy, Belgium, Malta, Sardinia and
Madeira. From Europe, ASF also spread to the Caribbean and
to Brazil. The spread of ASF outside Africa appears to have
been related to the movement of contaminated,
underprocessed pork products, and wildlife per se could not
be directly incriminated. Nevertheless, it is important to
prevent the introduction of this economically devastating
porcine disease from a wildlife source, and this may be
accomplished by the following precautions:
a) The movement or importation of all wild porcine meat
products from ASF-endemic countries/regions/zones should
ideally be prevented; alternatively, such products must be
adequately processed using an approved technique to ensure
biosafety.
b) All hides from wild porcines should be dipped in an
approved acaricide to prevent the passive transportation of
viable (potentially ASF-infected) argasid ticks.
c) Skulls and tusks must be cleaned of all soft tissues, and
then boiled for 4 5 minutes, or immersed in 5% formaldehyde
for 2 4 hours. Lipid solvents, detergents, oxidising agents and
substituted phenols are also effective.
Rinderpest
Rinderpest is primarily a disease of domestic cattle which is
capable of 'spilling over' into non-domestic ungulates during
cyclical epizootics. Previous records indicated that once the
disease had been controlled in cattle, it disappeared from
surrounding wildlife populations ( 2 7 ) . More recenüy,
however, events in East Africa have indicated that the role of
wildlife may not be so straightforward. Serological surveys in
the 1970s and 1980s suggest that certain strains of rinderpest
may cycle in certain wildlife populations and may be
maintained independently of cattle for variable periods of
time (24). Moreover, isolates from the most recent outbreaks
in wildlife in East Africa (1995 to 1997) have been genetically
fingerprinted and have proved to be identical to the strain
isolated during the last outbreak in the 1980s, despite the
absence of any identifiable disease in cattle in the intervening
period. A more cautious reappraisal of the role of wildlife in
the epidemiology of rinderpest is thus required.
The rinderpest virus is, however, relatively fragile and at
tropical ambient temperatures survives for only a few hours
outside the host (26). Carcass decomposition inactivates the
virus in one to three days (10). Being enveloped, the virus is
readily inactivated by lipid solvents, and is sensitive to light,
ultraviolet radiation, heat and extremes in pH. Infectivity is
also destroyed by most disinfectants.
Importation of fresh carcasses and meat products from an
infected zone/country does constitute a finite threat, and at
least one epidemic has been attributed to this source (1). In
Rev. sci tech. Off. int Epiz., 16(1)
frozen meat, the virus persists for much longer than in fresh
meat and is therefore a risk to swill-fed pigs (25). Infectivity
disappears rapidly from adequately dried infected hides (2).
As a result of the environmental lability of rinderpest virus,
the risk of importing the virus with meat and products of wild
game animals is minimal, and then only when meat from
acutely infected animals is rapidly frozen prior to
transportation.
A related virus which causes peste des petits ruminants (PPR)
infection has only once been reported in wildlife. An outbreak
occurred in a zoo in the United Arab Emirates, and mortalities
were recorded in wild sheep (Ovis orientalis
laristanica),
gazelles (Gazella dorcas), gemsbok (Oryx gazella) and a
Nubian ibex (Copra nubiana) (14).
Classical swine fever (hog cholera)
Classical swine fever (hog cholera) is known to circulate in
wild boar populations, and such an endemically-mfected
population is a potential risk to domestic pigs, either through
the food chain or by direct contact. The virus is relatively
robust and can survive in pork and processed pork products.
Survival can be prolonged for months when meat is stored
cool, or even for years when stored frozen (28).
Preventive measures include prohibiting the importation of
insufficiently cooked pork and pork products from infected
countries.
Common arbovirus diseases of ungulates
In Africa, the common arbovirus diseases of ungulates include
Rift Valley fever, bluetongue and African horse sickness.
These endemic diseases which are indigenous to Africa have
all been shown to cycle in wild ungulate populations, which
were probably the natural hosts for the viruses before the
arrival of pastoral man with his domesticated livestock.
Infections with these viruses in African wildlife are generally
subclinical, and because of the non-contagious nature of the
infections in animals, as well as the pH sensitivity of the
viruses, wild animal tissues and products, even from infected
animals, are unlikely sources of infection.
Transmissible spongiform encephalopathies
Spongiform encephalopathies have been documented in
farmed and free-ranging white tailed deer
(Odocoileus
virginianus), mule deer (Odocoileus hemionus) and wapiti
(Cervus canadensis) in North America since the late 1960s.
Chronic wasting disease has been reported from the states of
Colorado and Wyoming, and more recently in a Rocky
Mountain elk (Cervus elaphus nelsoni) in Saskatchewan,
Canada (this animal originated from South Dakota) (20). As
an animal health protection measure, carcasses from victims
of this disease should be prevented from entering the
commercial farm-animal feed production chain.
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Rev. sci tech. Off. int. Epiz., 16(1)
Bacterial diseases
Anthrax
Anthrax has been documented in many species of wild
animals from various taxa, including: artiodactyls,
perissodactyls, proboscids, carnivores and primates ( 1 3 ) .
Anthrax also has an almost world-wide distribution and has
been described in wildlife in various parts of Africa, Eastern
and Western Europe, Asia, the Pacific Rim and North and
South America (4, 6 ) . Vaccination and other animal health
measures have resulted in a lower incidence of anthrax in
domestic livestock in many countries, but an endemic
situation with interspersed cyclical epidemics still exists
among free-ranging wildlife in the so-called 'anthrax belts'.
The anthrax bacillus is notoriously resistant to environmental
extremes and may survive for decades in organic materials.
The vegetative bacillary form is killed by heating to
temperatures of 60°C for 3 0 minutes ( 5 ) . By contrast, the
spores are highly resistant to heat treatment (without
pressure), as well as to exposure to alcohols, phenols,
quaternary ammonium compounds, acids and alkalis.
The terminal septicaemic nature of anthrax ensures that most
organs of the victim are infected, and therefore all parts of the
carcass (including hides, bones, horns and hooves) are
potentially infectious. Preventing importation of wildlife
products from endemic areas (especially during epidemic
cycles) is therefore important. Such products should never be
allowed to enter the domestic animal food chain. It must be
remembered that anthrax-contaminated bone meal has been
shown to still be infective after being steam-treated for 15
minutes at 115°C or treated with dry heat (140°C) for 3 hours
(12).
Bovine tuberculosis and bovine brucellosis
Both of these significant bacterial diseases have been reported
in free-ranging and fanned wildlife, on several continents. The
heat-labile nature of the causative organisms, combined with
their predilection for visceral organs and lymph nodes makes
them unlikely animal health risk candidates when importing
wildlife products.
Macroparasitic diseases
Echinococcosis/hydatidosis
This parasitic infection is frequently reported in natural
ecosystems in which the definitive hosts are indigenous
carnivores with adult tapeworms present in the small
intestine. In these ecosystems, herbivorous prey animals
perform the role of the intermediate hosts in which hydatid
cysts develop following ingestion of vegetation contaminated
with infected predator faeces. The movement of raw predator
hides contaminated by faecally-borne gravid proglottids, or
the movement of raw cyst-containing organs, may result in
directly or indirectly linking the sylvatic and synanthropic
cycles through the infection of domestic livestock or
carnivorous companion animals.
Trichinellosis
Infection with Trichinella spp. has been diagnosed in the flesh
of many wild carnivores and some wild swine. The raw,
undercooked, dried or cold-smoked meat of these infected
animals are potentially infectious to carnivorous or
omnivorous companion animals.
Ectoparasitoses
Ectoparasitoses may constitute an animal health problem if
untreated wet hides from wild animals are imported. This
problem may be associated with importing an exotic
ectoparasite per se (e.g. alien ixodid or argasid ticks, mites, lice
or screw worms) or the problem could be associated with the
importation of a disease vector which may or may not be
infected with an alien pathogen, e.g. heartwater (cowdriosis),
tularaemia, babesiosis or ehrlichiosis. Untreated wet hides
may also be a source of dermatomycoses or pox viruses.
Conclusion
In general, with the notable exceptions of the individual
diseases listed, the animal health risks associated with the
movement of wildlife products are infinitely less than those
associated with the movement of live animals. It behoves the
regulatory authority of the importing country to ascertain if
any of these diseases are present in the country/region from
which the products originate, and to take appropriate
measures to prevent the importation of these disease agents.
However, it should also be remembered that since disease
surveillance in free-ranging wildlife populations is often
difficult and frequently inadequate, the decision-maker
should preferably err on the conservative side when
considering the importation of products derived from known
wildlife host species, when no reliable data is available.
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Rev. sci tech. Off. int. Epiz, 16(1)
Risques zoosanitaires liés au transport et à l'utilisation de produits
dérivés d'animaux sauvages
R.G. Bengis
Résumé
Les risques zoosanitaires liés aux échanges de produits dérivés d'animaux
sauvages sont infiniment moins importants que ceux liés aux déplacements
d'animaux sur pied. Très peu d'agents pathogènes survivent, en effet, aux
importantes variations de température, de pH, d'hygrométrie et d'osmolarité
survenant après abattage ou liées aux procédés de conservation, tels que le
marinage, le fumage ou le séchage. Cependant, certains agents pathogènes (par
exemple les virus de la fièvre aphteuse, de la peste porcine classique et de la
peste porcine africaine, ainsi que le bacille de la fièvre charbonneuse) résistent à
ces modifications du milieu et constituent donc un risque zoosanitaire limité en
cas d'importation de produits crus, mal cuits ou mal conservés et provenant
d'animaux sauvages infectés.
Des agents pathogènes moins résistants, tels que le virus de la peste bovine,
peuvent rester infectieux dans les produits d'origine animale lorsque ceux-ci
proviennent d'animaux souffrant d'une infection aiguë et qu'ils ont été congelés
immédiatement. Les agents de maladies macroparasitaires, telles que la
trichinellose et l'échinococcose-hydatidose, présents dans les tissus non traités
d'animaux sauvages atteints, présentent un risque d'infection pour les animaux
de compagnie, carnivores ou omnivores. Des ectoparasites étrangers peuvent
également être introduits dans un pays, avec les maladies infectieuses dont ils
sont les vecteurs, à l'occasion de l'importation de peaux vertes non traitées.
L'auteur étudie le cas des principaux agents pathogènes rencontrés chez les
animaux sauvages en liberté, qui doivent être pris en considération lors de
l'importation de produits dérivés de la faune sauvage et provenant de zones
d'endémie ou d'épidémie.
Mots-clés
Agents pathogènes - Commerce international - Faune sauvage - Produits d'origine
animale - Risques - Santé animale.
Riesgos zoosanitarios asociados al transporte y el uso de
productos derivados de la fauna salvaje
R.G. Bengis
Resumen
Los riesgos zoosanitarios asociados a los intercambios de productos derivados
de la fauna salvaje son infinitamente menores que los que entraña el movimiento
de animales vivos. Son muy pocos los patógenos lo bastante resistentes como
para sobrevivir a los notables cambios de pH, temperatura, humedad y
osmolalidad que se siguen de la muerte del animal o que acompañan a procesos
de conservación como el adobado, el ahumado o el secado. Ciertos patógenos,
sin embargo (por ejemplo los virus de la fiebre aftosa, la peste porcina clásica o la
peste porcina africana, así como el bacilo del carbunco bacteridiano), resisten a
estos cambios ambientales y constituyen un riesgo zoosanitario finito en el caso
de importación de productos crudos, semicrudos o en semiconserva procedentes
de animales salvajes infectados.
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Rev. sci tech. Off.int.Epiz., 16 (1)
Aunque menos resistentes, otros patógenos (como el virus de la peste bovina)
pueden conservar su infecciosidad en el interior de derivados animales en el
caso de que éstos procedan de individuos con infección aguda y sean
congelados inmediatamente. Cuando están presentes en tejidos no procesados
de animales salvajes enfermos, algunas enfermedades macroparasitarias como
la triquinelosis o la equinococosis/hidatidosis resultan potencialmente
infecciosas para los animales de compañía carnívoros u omnívoros. La
importación de cueros no tratados, por su parte, puede acarrear la introducción
de ectoparásitos extraños y/o la aparición de las enfermedades infecciosas de
las que son vectores.
El autor examina una serie de importantes patógenos que afectan a la fauna
salvaje en libertad y cuya eventual presencia convendría tener en cuenta a la
hora de importar productos derivados de animales salvajes desde países
infectados, ya sea de forma endémica o epidémica.
Palabras clave
Comercio internacional - Fauna salvaje - Patógenos - Productos de origen animal Riesgo-Sanidad animal.
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