D8371.PDF

Rev. sci. tech. Off. int. Epiz., 1988, 7 (4), 783-795.
Research on wildlife diseases:
is a reappraisal necessary?
W. PLOWRIGHT *
Summary: Past antipathy or apathy to research on wildlife infections and
diseases (they are not synonymous) has probably been based on the belief that
veterinary and paraveterinary workers are almost entirely concerned with diseases
transmissible to domestic animals and man. There is, however, great scientific
and practical potential in studying diseases of free-living animals per se as an
important branch of their ecology, essential to their sound conservation and
economic exploitation.
From the present base there are considerable difficulties in increasing the
veterinary contribution to research on wildlife: the recognition of disease is not
easy; notification may be delayed or is suppressed; some biologists, the lay press
and the public seem to find it easier to understand "pollution" than infectious
disease wild animals which are sick tend to die and to be removed very quickly.
Wildlife veterinarians act primarily as providers of an emergency service
but they could play a much more important part in wildlife programmes. They
require continuous access to animal populations to detect low levels of, or
inapparent but significant, infection. Additional, basic training in epidemiology,
ecology and conservation techniques is highly desirable for them and many
wildlife biologists would benefit from a better knowledge of infectious diseases.
The most important methods for monitoring microbial infections in wild
animals are discussed in relation to some past and present epizootics. The
Resolutions of the 56th General Session of the OIE are to be welcomed as a
step in the right direction.
KEYWORDS: Animal diseases - Animal production - Animal welfare -
Ecology - Epidemiology - Veterinary research - Wild animals.
INTRODUCTION
The theme of this issue of the OIE Scientific and Technical Review, "Wild animal
diseases transmissible to domestic animals" is, in itself, a reflection of the
overwhelming need for a reappraisal of the attitudes and role in wildlife biology of
those with special knowledge of animal disease. The unfolding saga of the recent
seal mortality in Western Europe, as judged largely by press and television reports,
on which most of us have perforce depended, shows how infrequently veterinarians
and their scientific co-workers are regarded as the experts by the media, the public
or those confronted more immediately by a spectacular epidemic decimating some
of our largest mammals.
* Whitehill Lodge, Reading Road, Goring, Reading RG8 OLL, England.

784
It is an objective of this paper to examine some of the reasons for this state of
affairs and to suggest ways in which veterinary and paraveterinary expertise can be
better equipped and applied to problems of disease in wildlife, whether transmissible
or non-transmissible. The examples quoted bear inevitably a personal bias; they reflect
an initial experience in Africa with major plagues transmissible to domestic species,
and recent data on spectacular lethal infections of wildlife.
At the opening of the Third International Wildlife Disease Conference in 1975,
the President, Milton Friend, referred to the difficulties of pursuing wildlife studies
in these words: "resistance or apathy towards controlling wildlife disease arises
because:
1. seldom is this action initiated primarily for the direct benefit of wildlife;
2. the action may be at the direct expense of wildlife;
3. there has been little to demonstrate that wildlife diseases can be controlled in
free-living populations;
4. the role of disease in the population dynamics of wildlife species has not been
adequately documented" (15).
Veterinary workers who have experience of investigating disease in wildlife or,
more particularly, inoffensive infections of wildlife which are more serious when
transmitted to man or his domestic animals, will recognise this "resistance or apathy"
and the justice of these complaints.
In North America, for which Friend was speaking, the situation is more favourable
than in Europe. Wildlife research in the USA began in the early 1900's at the Bureau
of Biological Survey, later to become the US Fish and Wildlife Service. The Wildlife
Disease Association (WDA), which published its first quarterly Bulletin in 1965, soon
to become the Journal of Wildlife Diseases, was "dedicated to the conservation of
wildlife through sharing the study and understanding of diseases of wild animals.
The object of the Association is to advance knowledge of the effect of infectious,
parasitic and physiologic diseases and other factors upon the health and survival of
free-living and captive wild animals, upon populations of wild animals and upon their
relationship to man". In this statement there is a conspicuous omission of any direct
reference to diseases transmissible from wildlife to man or his domesticated animals
or vice versa, although this may be covered by the phrase "their relationship to man".
The primary purpose of this article is to focus attention on infections and diseases
of wildlife per se. Microbiologists, parasitologists, toxicologists, specialists on nutrition
and metabolic disease as well as general epidemiologists and others should all be
brought to recognise the practical necessity for independent study of wildlife pathology
in its broadest sense and a vigorous development of its scientific potential.
DIFFICULTIES IN THE RECOGNITION OF INFECTIOUS DISEASES
IN WILDLIFE
It is indisputable that the level of disease and mortality in a free-living population
usually reaches severe or even catastrophic proportions before it is noticed and
recorded. The reasons for this are manifold. They include the relative isolation and

785
inaccessibility of wildlife populations. For example, rabies was estimated to have killed
30,000 to 50,000 greater kudu in the years 1977 to 1983, spreading out from the
Okahandja area of Namibia; furthermore, it was found to spread experimentally by
the oral route (20). Laws and Taylor (32) reported an 85% mortality amongst 2,500
crabeater seals (Lobodon carcinophagus) on sea ice near the tip of the Antarctic
Peninsula between 4 September and 21 October 1955; the sledging party which
discovered them noted abortions and concluded the disease was probably due to an
unidentified virus (31). There are press reports that 1,000 of the 6,000 hippopotamuses
in the Luangwa river valley in Zambia died of a disease, never officially notified but
thought to be anthrax, in an unknown period up to January 1988; the infection was
stated to have spread to elephant, buffalo, kudu, puku and Thornycroft's giraffe.
Surprisingly, a pack of "wild dogs", presumably the African hunting dog (Lycaon
pictus), a species which is becoming rare and on the threatened list, was said to have
been reduced to a single adult survivor with pups (23).
Another reason for the paucity of recorded outbreaks of infectious disease in
wildlife may be the failure to call in qualified investigators before or at the time of
epidemics. This omission is sometimes, unfortunately, attributable to a vested interest
in incriminating other more "popular" causes, such as chemical pollution, along with
real difficulties in recognition of its infectious character and even a desire to conceal
the existence of transmissible disease, ostensibly in the interests of the animals
themselves.
As an example of the first two of these factors in operation, Smith (53) reported
the history of "Western duck sickness" which caused tremendous mortality from
1910 onwards in waterfowl on lakes and mudflats of the western USA. It was not
until 1930 that the original attribution to alkali poisoning from lakes with high salinity
(e.g. the Great Salt Lake) was shown to be mistaken and type C botulism confirmed
as the cause. Similarly, the death of 50,000 birds, including 80% of the spoonbills,
occurred in 1973 in the Coto Doñana Reserve at the mouth of the Rio Guadalquivir
in Spain; whilst attributed at first to pesticide poisoning it was later shown to be due
to type C botulism (53, 54). A similar sequence of events was recorded in the Mersey
estuary (England) in Autumn 1979, where lead poisoning was at first invoked as the
cause of death in 2,400 water birds, whereas later bacteriological investigation showed
the probable involvement of type C botulism (55).
It is interesting to observe parallels with the recent seal morbillivirus epidemic
off Western European coasts (40). Press reports have continued to emphasise an
imputed association with pollutants, especially polychlorinated biphenyls (PCB's),
DDT, lindane and dioxin, etc. On 27 September 1988, Nicholson-Lord reported in
The Times (London) that "scientists have argued that pollution cannot be ruled out
as an underlying cause of the epidemic. Although the trigger was the canine distemper
virus (CDV), toxins may have harmed the immune system" (36). This was after a
conference in London on 11 August which decided that the primary cause "on the
basis of epizootiological observations is generally believed to be infectious" (41). A
later report of 27 deaths in a population of 220 grey seals in the Dee estuary (England)
between March and September 1988, postulated that this was possibly due to an
unidentified virus unrelated to CDV and "caused by mercury pollution" (37).
On the question of concealing disease in wildlife in the belief that this is in their
best interests, two examples will suffice. Long after a high incidence of bovine
tuberculosis in badger populations in parts of south-west England had been confirmed

786
pathologically and bacteriologically as a source of infection for cattle, there were
strident objectors to the control measures, which involved the killing of infected
badgers. Some of them, lay-persons admittedly, strongly denied that tuberculosis did
in fact occur in badgers (62) and did everything within their power to conceal its
presence.
In East Africa, where there was a long history of wild ungulates serving as a
reservoir and means of dispersal of rinderpest virus (7, 45), there is little doubt that
a tendency grew up on the part of some authorities in the National Parks and game
reserves to minimise and delay reports of mortality in rinderpest-susceptible species
in the belief, not unfounded, that publicising the information would lead to unwanted
investigation of these species by the veterinary authorities and subsequent pressure
to control their movements and numbers by rather drastic measures. This tendency
for development of a conflict of interests between veterinarians and conservationists
was also commented on in a more general sense by Woodford (59). It later diminished
with the recognition of a common interest in eradication of a lethal disease but it
has probably not disappeared.
In South Africa, a long-standing record of moderate attitudes on the part of the
veterinary authorities (56, 9, 11) has been, apparently, conducive to better
collaboration with those in National Parks, etc. (60) leading to some excellent examples
of the part which the investigation of disease or methods for its prevention in wildlife
can contribute to conservation (anthrax in wildebeest in the Etosha National Park,
Namibia: 12, 5; development of anthrax immunisation from helicopters, of roan
antelope in the Kruger National Park, South Africa: 10).
Other important reasons for the failure to observe and report disease in wild
animals are the frequent lack of easily recognisable signs, the rapid deterioration of
animals which become sick and die and their early detection and removal by scavengers
leading to the "impression that wild game populations are not frequently decimated
by disease" (60). It is remarkable, for instance, that approximately 13,000 of 16,000
juvenile buffaloes in a total population of 61,000, died in the Serengeti National Park
of Tanzania in the years 1970-71 and 1971-72 without severe morbidity becoming
apparent on continuous close observation. This was in the absence of rinderpest, which
up to 1963-65 had been a major external "regulator" of the buffalo population,
possibly since the great panzootic of the early 1890's (51). The removal of this regulator
was considered to be largely responsible for the rapid increase in the population -
or "eruption" - which followed up to the early 1970's (52); nevertheless catastrophic
or striking mortality in buffaloes had been observed very irregularly and usually in
localised form.
"Scavengers" in the sense employed by Young (60) include predators such as lion,
leopard, hyenas and jackals, as well as vultures, etc. and their ability to recognise
relatively minor incapacity in their prey is well known. In early attempts to immobilise
and fit identification collars on species such as hartebeest and wildebeest in Kenya,
it was found that a large proportion of the subjects "disappeared" very quickly. It
was then discovered that the premature release of immobilised animals led to their
rapid recognition, probably from gait abnormalities, and a speedy despatch by the
ever-present hyenas. It is nevertheless debatable whether predation generally is selective
for unhealthy individuals (6) and May (34) remarked about this popular ecological
notion as follows: "I have yet to see the suggestion that microparasites are beneficial
in supplying weakened prey to sustain predator populations". The rapidity with which

787
wildlife species die was supported by evidence from the Pretoria zoo; in spite of daily
inspections, 80% of 280 mammals which died had shown no premonitory signs and
the figure could be higher in wild birds and reptiles (61).
THE ROLE OF WILDLIFE VETERINARIANS
It has been evident for many years in Africa, with its great resources of wildlife,
that there was a need for veterinarians who concerned themselves entirely with their
diseases or infections. The first "wildlife veterinarian" to be appointed in Kenya under
the United Nations Development Programme (through the FAO) arrived in 1967;
the account on his activities (13) contains much that was relevant to defining the
functions of the office then and to-day.
Thus it was recognised that wildlife were among the most important national assets
and that their diseases needed to be studied in depth whether or not they were
transmitted to domestic animals. They also needed to be viewed consistently and
primarily in an ecological context; national parks and reserves were delineated and
protected (thus not a completely "natural" environment) and monitoring the health
of wildlife populations was an important factor in the successful exploitation of the
resources. A team approach was necessary, so that consultation and cooperation with
biologists allowed the best use of restricted materials, obtained, for example, in the
course of culling operations. Again, inspection of wildlife products was necessary
if they were destined for human consumption - or, incidentally, to control movement
of agents of animal disease.
This broadly based and positive approach to the functions of wildlife veterinarians
may be compared with a recent statement of its objectives and scope from the
Veterinary Specialist Group (VSG) of the SSC/IUCN (24). This affirmed that the
"study of disease conditions in wildlife is a relatively new discipline... still in the
descriptive stage", and concluded that the first important concern of members was
"the justification for veterinary intervention in cases of wildlife disease or injury".
The statement recognised that "disease is part of the ecosystem and plays an important
part in natural selection" but that "there are examples where intervention is plainly
justified, as for instance in populations of seriously endangered species...".
The subsequent references to parasitism, deficiency diseases and "zoonoses", the
effects of overcrowding and disease in species reintroduced to the wild are depressingly
those of a "service" profession, rather than one which actively participates, as of
right, in research on all aspects of the impact of wildlife disease in ecology and
conservation and contributes to its understanding. The second major concern of the
VSG is said to be "immobilising and tranquillising of wild animals", undoubtedly
a very important technique, but hardly more than that and certainly not elevating
the practitioners out of the service role.
It is in this context that the recent Resolutions from the 56th General Session of
the Office International des Epizooties (39) should be welcomed, as going some way
towards recognising the intrinsic economic and ecological importance of wildlife
diseases per se, promoting their study and accepting them as proper subjects for the
agenda of Conferences. What will need to be determined next is the source of funds