Bovine TB and Human HealthWhat is Bovine Tuberculosis?
Bovine tuberculosis (TB) is a disease caused by the bacterium Mycobacterium bovis, which is different from the strain of mycobacterium that usually infects humans. In the U.S., the disease is found primarily in cattle, captive cervidae (deer and elk), bison and goats, but can affect any warm-blooded animal, including humans.
Human Health Factors
In the U.S., humans contracting bovine TB from animals is rare. However there was one human case, diagnosed in 2002, that was linked to the unique strain of M. bovis found in the cattle and deer of Northern Lower Michigan. People who come into contact with TB-infected animals are encouraged to take extra precautions and contact their personal physicians or the Local Health Department concerning the need to have regular TB skin tests. Extra precautions while handling animals include wearing disposable latex gloves and washing your hands afterward. A positive skin test reveals exposure, not infection, and does not identify the type or source of the exposure. Bovine TB can be effectively treated in humans, so it is crucial to contact your physician if you have been exposed. Health officials have confidence in the state's meat and milk supply. By continuing to eliminate TB-infected animals from herds, paying close attention to the meat inspection and pasteurization processes, and using proper food handling and good management practices, the chance of bovine TB transmission from animals to humans is virtually eliminated.
Bovine Tuberculosis in Michigan
Bovine TB is not a new problem in Michigan. TB was frequently found in dairy and beef cattle in Michigan, and many other states, through the mid 20th century. In fact, Michigan was not declared free of bovine TB in cattle and bison until 1979. However, bovine TB has historically been a rare disease in wild deer. Prior to 1994, only eight wild white-tailed or mule deer had been reported with bovine TB in North America. Michigan is thought to be the only place on the continent where the disease has become established in the wild white-tailed deer population. In June 1998, bovine TB was confirmed in a beef cow in Alpena County. Since that time the disease has been confirmed in multiple cattle herds in Michigan. Bovine TB has also been detected in numerous captive and wild deer as well as elk and wild carnivores such as coyote and bobcat, and in one case a domestic outdoor cat.
While it is possible to transmit bovine TB from animals to people, the likelihood is extremely rare. It is highly unlikely that a person field-dressing or eating the cooked meat of animals infected with bovine TB would become infected. The TB bacterium is very rarely found in meat (muscle tissue). Since bovine TB is primarily spread through respiration, the bacterium is generally found in lung tissue. As a precaution, however, all meats, including hunter-harvested deer, should be thoroughly cooked to an internal temperature of 165 degrees F for 15 seconds to kill bacteria. If the lungs, ribcage or internal organs from wild deer look abnormal (multiple tan or yellow lumps), the meat should not be eaten and the deer should be taken to a Michigan Department of Natural Resources check station. Experts at MSU are confident that meat inspection systems will continue to protect consumers against contracting bovine TB from properly processed foods. Inspection and processing of all meat being offered for sale to consumers follows stringent requirements that guard the safety of the food supply. All livestock in Michigan destined for table use are cooperatively scrutinized by the Michigan Department of Agriculture and the US Department of Agriculture before and after processing to assure the meat is disease-free before being sent to the consumer market. Consumers also play an important food safety role once meat leaves the retail counter. Prudent handling such as proper hand and utensil washing, proper refrigeration, and using a meat thermometer to cook meat to the proper temperature are all very important.
Milk is a safe, wholesome consumer product used as a beverage and in ice cream, yogurt, cheeses and other dairy products. From the time milk is taken from the farm bulk milk tank until it arrives on the store dairy shelf, it undergoes continuous scrutiny. Michigan licensed milk haulers collect a sample from each farm bulk milk tank for quality testing. When the milk truck arrives at the processing plant, another sample from the load is tested for antibiotics. The pasteurization process heats the milk by either the continuous (at least 161 degrees F for at least 15 seconds) or batch (at least 145 degrees F for at least 30 minutes) process to kill pathogenic bacteria that may be present. This process is verified by MDA and each pasteurizer is thoroughly checked according to the strict testing requirements of the U.S. Food and Drug Administration's Pasteurized Milk Ordinance (PMO). The two time/temperature combinations have been proven, over years of research, to destroy the most heat-resistant disease-causing organisms that might be found in the raw milk supply. In addition, post-pasteurization handling, packaging and shipping procedures follow a stringent sanitation regimen that is monitored regularly by MDA dairy inspectors. Pasteurization of milk was originally implemented in the United States to specifically kill the bovine TB bacterium and other disease-causing organisms. Pasteurization kills bovine TB. Farm families and others are reminded not to drink unpasteurized milk or to give it to other animals on the farm. From January 2000 through December 2003, state and federal veterinarians tested all cattle, goats and bison herds in Michigan for bovine TB. During the bovine TB screening process, if an animal has a specific reaction to the bovine TB test, it will be classified as a reactor and removed from the herd for laboratory tests. Bovine TB cannot be confirmed until the results of several laboratory tests are available. However, to protect other animals in the herd and herd owners, the animal is not allowed to remain on the farm. As an additional precaution, MDA works with dairy shippers to make sure that milk from TB-reactor cows does not enter the milk supply. Under the federal PMO, milk from other animals in the herd may remain in the marketplace.
A Commitment to Safety
The MDA, the Michigan Department of Natural Resources, and their partner agencies maintain a strong commitment to eradicating bovine TB from Michigan livestock and deer. In keeping with its long-standing tradition of making food safety a top priority, MDA pledges an equally rigorous effort to continue ensuring the safety of venison, beef and milk, through comprehensive testing, monitoring and educational efforts from the farm or processing plant to the retail store.
MDARD Animal Health Liaison (517) 241- 4724
MDCH Communicable Diseases (517) 335-8165
DNR Wildlife Disease Lab (517) 336-5030
MSU Contact your local county extension agent or ANR Communications at (517) 432-1555
USDA -(517) 324-5290