Bovine tuberculosis in Michigan (Proceedings)


Bovine tuberculosis in Michigan (Proceedings)

Aug 01, 2008

Bovine Tuberculosis (bTB) is an infectious bacterial disease that poses a risk to domestic livestock and wildlife in the United States (U.S). In 1917 the U.S. government began a comprehensive national bovine TB eradication program. The disease has been nearly eradicated from livestock in the U.S., but periodically areas of infection resurface. As part of the United States bTB eradication program, Michigan was declared free of bTB in cattle in 1979. In 1975, a 9-year-old female white-tailed deer located in Northeast lower - Michigan, was found to have lesions consistent with bovine tuberculosis (bTB). Subsequently Mycobacterium bovis was isolated. This was believed to be an isolated case and no further testing was done on the surrounding livestock or deer. Historically, bTB in wild deer has been rare in the United States. Each of the 8 cases reported prior to 1995 was found to be associated with exposure to infected cattle, bison, captive elk, or feral swine and no evidence of further transmission between white tail deer was evident.

In 1994, a hunter in Northeast Michigan, shot a 4-year-old male whitetail deer, which had lesions consistent with TB, and M. bovis was isolated. The deer was harvested approximately 10 miles from the site of the 1975 infected deer. Because of Michigan's bTB free status in cattle, it was decided to test the surrounding cattle and captive cervid herds. No evidence of bovine TB was found. In the fall of 1995, surveillance of hunter-killed deer was initiated and 27/814 deer were found to be culture-positive for bovine TB.

The Bovine TB Eradication Project was established as a multiagency partnership to investigate the issues. The project consisted of personnel from the United States Department of Agriculture (USDA); the Michigan Departments of Agriculture (MDA), Natural Resources (DNR), and Community Health (MDCH); and Michigan State University (MSU).

Since 1995, wildlife surveys have been conducted by the DNR in the surrounding area. Cervid and noncervid carcasses and/or heads are examined grossly for lesions. Suspicious lymph nodes and tissues from cervids were submitted to the National Veterinary Services Laboratories (NVSL) or MDCH for culture and to MSU and NVSL for histopathology.

Figure 1: Location of bovine TB positive animals in Michigan, 1975-2003.
As of the end of 2007, over 161,000 whitetail deer and 1,876 elk have been examined for bTB. From these animals, 593 white tailed deer and 5 elk have been identified as positive for bTB. In addition, several non-cervid species have been surveyed primarily from Northeast Michigan and include (number of positive in parentheses) badgers, black bears (7), bobcats, coyotes (18), feral cats, feral dogs, gray fox, mink, opossum (2), otters, porcupine, raccoons (8), red fox (3), skunks, snowshoe hare, and weasel. The majority of the infected wildlife has come from 12 northeastern Lower Peninsula counties in Michigan (Figure 1). In the winter of 2008, a single white tailed deer was found infected with bTB in the southern part of the lower peninsula of MI. This is only the third positive deer found outside of Northeast MI and represents the most distant positive animal from the core of the bTB outbreak. A 10 mile circle test of all cattle around this infected deer has not found any indication of infected cattle to date.