Evaluation of Potential Shedding of Mycobacterium bovis in Free-Ranging Raccoons

Abstract

Author(s): Berentsen, Are R.; Dunbar, Mike R.; Marks, David R.; Robbe-Austerman, Suelee | Abstract: Bovine tuberculosis (bTB) is a contagious disease capable of infecting wildlife, livestock, and humans. While once common in U.S. livestock, the disease has historically been rare in wildlife. However, in Michigan’s Northeastern Lower Peninsula (NELP), bTB is endemic in white-tailed deer, and evidence suggests transmission to cattle. The disease has also been documented in other wildlife species including raccoons, which frequent areas used by domestic cattle. Such interactions could facilitate transmission of bTB, but whether free-ranging raccoons shed the causative agent, Mycobacterium bovis, is unknown. We trapped raccoons on private and public land in 5 counties in the NELP from which we collected tissue samples, oral/nasal swabs, and fecal samples to determine if raccoons shed M. bovis. Culture results from 2 of 144 usable tissue sample submissions were positive for bTB, suggesting an apparent local prevalence of 1.4%, a decrease from previous estimates. Using currently available culturing techniques, swabs and feces from one tissue culture-positive animal were negative for M. bovis. While this small sample size of positive animals makes definitive conclusions difficult, we believe that although raccoons may serve as a reservoir or a spillover host for bTB, transmission risk to cattle is minimal. Further research into this arena, as well as continued refinement of culturing techniques to detect low levels of M. bovis, is warranted.