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Bovine TB is an infectious disease that is caused by the bacterium Mycobacterium bovis (M. bovis). Bovine TB primarily affects cattle, however, other animals may become infected. In addition to cattle, bovine TB has been reported in a variety of mammals worldwide and is established in populations of European badgers in the UK, cape buffalo in South Africa, brush-tailed possums in New Zealand, wood buffalo and elk in Canada, and white-tailed deer in Michigan. Until the disease was detected in white-tailed deer in Michigan in 1994, it has historically been very rare in wild deer.
Bovine TB is present in white-tailed deer in the northeastern part of Michigan’s Lower Peninsula. In May of 2010, bovine TB was found in a beef cattle herd in Fleming County. This was the first positive case in Kentucky since 1987. Wildlife surveillance around the affected premises did not detect any additional infected wildlife. In April of 2016, bovine tuberculosis was detected on a cattle farm consisting of two premises in Southeastern Indiana. As part of the response to that event, wildlife was removed and tested from the affected areas and a wild white-tailed deer doe removed from the affected premise tested positive for bovine tuberculosis. This marked the first time the disease was found in wild deer in Indiana.
Bovine TB is spread primarily through the exchange of respiratory secretions between infected and uninfected animals. This transmission usually happens when animals are in close contact with each other. Animals may also become infected with TB by ingesting the bacteria. Thus, animal density plays a major factor in TB transmission. Bacteria released into the air through coughing and sneezing can spread the disease to uninfected animals. Research also suggests that bovine TB can also be contracted from ingesting contaminated feed.
Bovine TB is a progressive, chronic disease. It can take months to years from time of infection to the development of clinical signs. Coughing, nasal discharge, and difficulty breathing can be seen in advanced cases, where the lungs become severely affected. These signs can also be the result of other disease conditions in deer including pneumonia or hemorrhagic disease.
There are no effective vaccines for disease prevention and no effective medications for treatment of bovine TB in wild deer or elk. Instead, a combination of wildlife disease surveillance and population management strategies can be used to eliminate the disease if present in wild deer or elk.
Unlike most bacteria, bovine TB grows very slowly. The lymph nodes in the animal’s head usually show infection first and as the disease progresses, lesions will begin to develop on the surface of the lungs and chest cavity. In severely infected deer, lesions can usually be found throughout the animal’s entire body.
Bovine TB infected deer not showing lesions in the chest cavity can be diagnosed by performing a visual inspection of the lymph nodes in the deer’s head. Affected lymph nodes, when cut, will contain one or more variably sized pus-filled nodules. Suspicious looking lymph nodes are removed for further testing at approved laboratory facilities.
In the U.S. today, the threat of humans contracting bovine TB from animals is extremely remote. Bovine TB has not yet been detected in Kentucky. However, good field-dressing techniques are important to avoid contact with TB and other wildlife pathogens. The best way to insure your safety is to wear disposable rubber gloves when gutting a deer or elk and wash your hands after field dressing or handling raw meat. Special attention should be paid to the lungs and chest cavity where small lesions may be evident in an infected animal. As a precaution, all meats (including deer), should be thoroughly cooked to an internal temperature of 165 degrees F. This effectively kills all known bacteria, including TB and E. coli.
Hunters can help by reporting any unusual lesions to the Kentucky Department of Fish and Wildlife Resources wildlife veterinarian at 1-800-858-1549. If possible, keep the carcass or affected tissues on ice. We will advise you about the appropriate use of the animal and may collect tissues for diagnostic testing if warranted.