Foreign animal diseases and Canadian wildlife: Reasons for concern and the elements of preparedness

Reasons for concern

During an incursion of a foreign animal disease (FAD), susceptible wild animals may become infected and act as reservoirs and sources of new infections for livestock, thereby prolonging outbreaks and trade embargoes, complicating eradication and control efforts, and, thus, magnifying the economic harm to livestock and related industries. This is the potential importance normally accorded to wildlife in FAD planning. It is an important issue and, usually, it is discussed with the implicit assumption that, if necessary, livestock must be protected at the expense of wildlife.

Wild animals themselves can be harmed by FADs. They can experience morbidity and mortality, reproductive loss, and increased predation when FADs to which they are susceptible are introduced. As a result, a nation's natural capital, namely, its natural resources and associated ecologies and economies, can be significantly affected through the impact of disease on wild animals. Wild animals also can be harmed and diminished by FAD control activities when these include destruction, confinement, or harassment of wildlife. Thus, wild animals must be viewed, not just as potential sources of FAD for livestock, but also as potential victims of both the diseases and their control measures.

Some decades ago, the response of the general public to expressions of concern for the welfare of wildlife in the face of a potential FAD outbreak might have been that, unfortunate though it may be, wildlife interests simply must be set aside when diseases, such as foot and mouth disease (FMD), break out, because the economic consequences to the livestock industry are enormous if these diseases are not dealt with harshly and immediately. But societal values and economic realities have changed. Environmental quality, nature appreciation and associated tourism, fishing, hunting, and both subsistence and commercial food procurement based on wildlife are dominant public interests and very big business in Canada. It is no longer certain that society will place a higher value on the livestock industry than it will on its wildlife resources, if the latter is threatened by the former. Thus, wildlife interests must be fully integrated into planning responses to FAD incursions, if such planning is to be realistic and effective.

Foot and mouth disease serves as a timely example of the importance of incorporating wild animals in FAD response planning. It must be assumed that all wild artiodactyls (cloven-hoofed animals) can become infected with the FMD virus. A special publication on this topic listed 55 species of wild artiodactyls worldwide that are known to have supported natural infection with FMD virus (1). The list includes 7 of Canada's 12 wild artiodactyls: white-tailed deer, mule/black-tailed deer, wapiti (elk), bison, moose, caribou/reindeer, and feral pigs/European wild boar. It is almost certain that the other 5 native species — mountain goat, bighorn and Stone/Dall's sheep, muskox, and pronghorn — are also susceptible to infection.

Very little is known about FMD in these susceptible Canadian species. A small amount of information exists for white-tailed deer, and the large body of information about FMD in domestic pigs has been applied to feral pigs. White-tailed deer were infected experimentally with FMD in 1 experiment (2). The deer suffered typical clinical disease and shed virus for up to 11 wk. This duration of shedding virus may be long enough to keep the virus active in wild white-tailed deer populations for many months. The geographic range of the white-tailed deer in Canada is very large, extending from southern Labrador to British Columbia and the Yukon, and including all areas of major livestock production. The species is abundant over most of its range; for example, there are approximately 350 000 in Ontario and 250 000 in Saskatchewan.

Populations of feral pigs exist in Canada, but their number, distribution, and biology are poorly documented. These are pigs that have escaped from farms and have formed self-sustaining, reproducing populations. For example, about 500 feral pigs, mostly derived from imported European wild boar, are present in Manitoba. In the United States, feral pig populations are very large and widespread. The range of the feral pigs in Manitoba is within about 100 km of a population of feral pigs in Minnesota. Pigs infected with FMD shed very large quantities of virus and produce aerosols of virus that can be infectious to other susceptible animals over distances of several kilometers. Foot and mouth disease in feral pigs has been the subject of considerable research and modelling. For example, Australian scientists have estimated that FMD will spread among feral pigs at a rate of about 2.8 km per day when pigs are at a fairly low population density (1 to 2/km²) (3).

The wild species in which FMD is best understood is the African buffalo, in which FMD infection is permanent. The African buffalo is a source of infection for cattle and also for other susceptible wildlife, most notably impala. The African buffalo is taxonomically and behaviorally rather close to the American bison. It is possible, therefore, that Canada's large and expanding populations of wild bison also might support long-term infection with FMD virus (4).

Wildlife and responses to FMD

During outbreaks of FMD in livestock during the past century, government authorities appear most often to have selected 1 of 2 different options regarding how wild animals should be considered:

Kill wildlife — Include all susceptible wild animals in eradication programs and attempt to kill them all in the eradication area. This was the basis for the killing of some 20 000 mule deer in California in 1924–1925 (5).

Ignore wildlife — Simply ignore wildlife when planning and implementing FMD control plans. Operationally, this seems to have been the most common response, and it seems to be based on 2 premises: the first, that it is impractical to try to eliminate wild animal populations; the second, that it is not necessary to be concerned about FMD in wild animals, because it is assumed that wild animals will not maintain the virus for long. Thus, controlling the disease in livestock should be sufficient to achieve total eradication.

There are at least 2 problems with killing wildlife. First, usually, it is not possible to kill enough animals quickly enough to make a difference to actual disease transmission. The relationship between the rate of disease transmission and the density of susceptible animal populations is not linear because of grouping behavior. Thus, it is necessary to kill a very large proportion of the total population to have any effect at all on the disease transmission rate. The number of animals that must be killed to reach this threshold level of effective population reduction is seldom known. Methods and personnel to kill large numbers of animals quickly are not usually available.

Second, society is intolerant of this action. Today, it is very likely that any government agency that tried to carry out a major slaughter of wild animals in order to protect the economic interests of the livestock industry would immediately be served with a court injunction. That injunction would as likely come from competing economic interests in tourism, nature viewing, and hunting as from environmental, conservation or animal rights groups. The value of wildlife to society should not be underestimated. In 1996, Canadians spent $11.0 billion on nature-related activities. This expenditure, together with the $700 million spent by visiting Americans, contributed $17.3 billion to gross business production and $12.1 billion to the gross domestic product (GDP) (6). For comparison, farm cash receipts for all livestock in Canada in 1996 totalled $13.9 billion, and the contribution to the GDP for the total of Canadian agriculture, including livestock, crops, and related service industries, was $12.3 billion (7). Thus today, killing wild animals to protect livestock from an FAD may be, simultaneously, impossible, illegal, and economically foolhardy.

But there also are problems with ignoring wildlife. First, to simply ignore wildlife in FAD control and response planning in Canada is also to court disaster. Again, using FMD as an example, Canada has large populations of 12 species of susceptible wild animals, many of which are expanding in number and range, and many of which intimately share habitat with the livestock industry. Whatever effect an FAD might have on wild animals themselves should they become infected, it absolutely would be harmful to a livestock industry dependent on international trade. The very real possibility of long-term and widespread infection of Canadian wildlife with FMD or some other FAD represents an enormous and unacceptable economic risk to animal agriculture and to all who derive their living from it.

The elements of preparedness

Effective planning for responses to FAD incursions must accord to wildlife the same degree of thought and detailed attention now given only to livestock. Such planning will require substantial activity on 3 related fronts: information, networks, and methods.

Information — Complete information about Canada's susceptible wildlife populations, for example, the 12 wild artiodactyls susceptible to FMD, must be gathered together in one place. The data must include geographic distribution, population densities, habitats, seasonal movements, and annual hunting and harvest statistics. All this should be assembled, mapped, posted online, and kept up-to-date. This is the information required to evaluate the risk and rates of disease transmission between livestock and wildlife, and the potential of disease to spread within wildlife populations. No such assemblage of data for these species in Canada currently exists. No federal government department has a mandate to manage these species nationally; their management is the mandate of provincial and territorial governments. The needed information is archived within some 14 or more different agencies and will take months to assemble for the first time. No credible, science-based FAD response plan can be made without this information.

Networks — Planning and implementing an FAD response requires the full participation of Canada's professional wildlife biologists. The highest level of expertise in modelling disease dynamics in wild animal populations exists within biological science units of universities and government wildlife agencies. In addition, provincial and territorial wildlife agencies have jurisdiction over most of the species of concern. Control measures that affect wildlife will fail unless they are planned with the participation and agreement of these agencies and, also, of the nongovernment organizations with vested interests in wild animals. For all these reasons, FAD response planners must develop an inclusive consultative network that provides both expertise and consensus on effective and acceptable disease management strategies and methodologies that can be deployed in the event of an FAD outbreak. The important players in this network will be people with whom, traditionally, regulatory veterinary authorities have had no contact whatsoever. Thus, it is a network that must be built from scratch, and built right now.

Methods — The wildlife consultative network described above should be deployed to develop a range of methods that could be used to reduce the risk of transmission of disease from livestock to wildlife in the event of an FAD outbreak, or to limit or prevent its spread among wild animals. These methods might range from effective fencing to exclude wildlife from infected premises to realistic and acceptable methods of rapid, local depopulation. They might include manipulation of hunting activity, radiotelemetry to measure animal movement during the outbreak, diversion of migration routes, and other techniques based on methods and knowledge in modern wildlife biology. This network also should establish the conditions and species for which the various methods would be appropriate and procedures to measure their effectiveness.

These 3 actions are both feasible and affordable, and are absolutely essential. With respect to the current pandemic of FMD, they should be implemented immediately. They will establish the necessary information, lines of communication, and science-based plans to achieve FAD preparedness. Anything less will not.