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| Non-Cervid Wildlife |
In 1995, bovine tuberculosis (TB) was discovered to be endemic in free-ranging
white-tailed deer in the northeastern Lower Peninsula of Michigan. The discovery
of endemic tuberculosis in deer coupled with the wide host range of
Mycobacterium bovis (M. bovis), the causative agent of bovine TB, provided the
impetus for a survey of other wild species present in the area. Wildlife species
selected for inclusion in the study were those non-cervid mammalian
species present in the area where deer had been found with bovine TB. Species
that have been tested in this survey are the American badger, black bear,
bobcat, coyote, feral cat, feral dog, gray fox, long-tailed weasel, mink,
opossum, porcupine, raccoon, red fox, river otter, snowshoe hare, and striped
skunk.
One thousand five hundred and fourteen (1,514) non-cervid animals were tested with seven black bear, four
bobcats, nineteen coyotes, two opossums, eight raccoons, and three red fox,
found to be infected with the bovine TB organism. The most likely source of
infection for these animals was through the consumption of tuberculous
white-tailed deer.
The finding of bovine TB in free-ranging non-cervid wildlife in North America,
although rare, is not unprecedented. Mycobacterium bovis was cultured from one
of 23 free-ranging coyotes collected near a bovine TB infected captive elk herd
in Montana in 1994. This was the first report of bovine TB in a coyote. No gross
or microscopic lesions were observed in this animal.
The number, extent, and distribution of tuberculous lesions in an infected
animal provides an indication of that species' ability to act as a reservoir of
infection for other animals, since successful disease transmission requires
excretion of the infectious agent from the host. While most mammalian species
are susceptible to bovine tuberculosis, only a few non-cervid species are
thought to be reservoirs of M. bovis. Brush-tail possums and ferrets in New
Zealand, and European badgers in England and Ireland are believed to be
reservoir hosts for M. bovis. These species develop extensive lesions containing
tremendous numbers of tuberculosis bacteria. Excretion of M. bovis has been
demonstrated from these species. Thus far, disseminated lesions with high
numbers of bacteria have not been found associated with native Michigan
non-cervid wildlife. The number of tuberculous non-cervid wildlife, the variety
of species involved, and the geographic spacing between the cases is more
indicative of disease spillover from free-ranging deer, the primary reservoir to
these non-cervid wildlife species, rather than endemic tuberculosis.
The white-tailed deer in Michigan is recognized as the primary reservoir host of
bovine TB. Once the disease is eliminated from the deer, the disease should die
out in the non-cervid species. As long as bovine TB exists in the wild,
free-ranging deer population, there will be some risk to local wildlife species
that feed on bovine TB-infected deer carcasses or gut piles.
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