The Michigan Department of Agriculture and Rural Development (MDARD) has confirmed a case of bovine tuberculosis (TB) in a dairy herd in Charlevoix County, located west of Michigan’s Modified Accredited Zone (MAZ), where the disease is known to be present in the state’s white-tailed deer population.
According to state officials, the detection followed identification of bovine TB in an adult cow at a USDA Food Safety Inspection Service-inspected processing plant. Through animal traceability efforts, officials traced the animal back to its herd of origin. Subsequent testing of the herd identified additional bovine TB cases.
“This latest detection of bovine TB highlights two important realities: how challenging the disease is to address; and why it is so crucial to use all of our tools for detection to swiftly identify cases and take actions to limit disease spread,” say Nora Wineland, state veterinarian for Michigan. “While finding a newly affected herd is never ideal, this case demonstrates our systems for detection and traceability are working, allowing us to quickly implement measures to protect animal health and public health in Michigan.”
MDARD reports an epidemiological investigation is already underway to determine whether additional cases may be linked to the affected herd. There are currently two TB zones within the state: a four-county area in northern lower Michigan called the Modified Accredited Zone, and the remainder of the state’s 83 counties is referred to as the Accredited Free Zone.
This is Michigan’s second confirmed bovine TB case in the past 13 months. The previous case was identified in a beef herd in Alcona County, located within the state’s Modified Accredited Zone, in January 2025. With this latest detection, a total of 84 cattle herds have been confirmed with bovine TB in Michigan since 1998.
What is Bovine Tuberculosis?
According to USDA’s Animal and Plant Health Inspection Service (APHIS), bovine tuberculosis is a chronic bacterial disease that can infect all mammals, including humans. It is caused by the bacterium Mycobacterium bovis and spreads through both direct contact between infected and uninfected animals and indirect exposure, such as contaminated feed, water or the environment.
The disease progresses slowly, often developing over several years. Infection typically begins in the lymph nodes before advancing to the lungs and chest cavity, where it can cause serious lesions.
While cattle are the primary host, the disease can also be present in white-tailed deer and elk, as well as bison, goats and certain carnivores, including coyotes.
The Symptoms
Unfortunately, infected cattle are typically asymptomatic. Detection usually occurs during live animal skin testing or, more commonly, at slaughter through our national slaughter surveillance program, according to USDA. If cattle or bison show clinical signs of tuberculosis, the disease has advanced to affect multiple organ systems, which is rare.
Can it be Prevented?
Bovine TB most often spreads through close contact, especially nose-to-nose interaction between animals, or when cattle consume feed or water that’s been contaminated. In most cases, herds become infected one of two ways: by bringing in an infected animal or through exposure to infected wildlife.
While the prevalence of tuberculosis in cattle is extremely low in the U.S., with an estimated prevalence of 7 per 1 million cattle screened, it can occur. Producers should work alongside their veterinarian to help create a biosecurity plan.
How is it Identified?
According to APHIS, the primary source of tuberculosis surveillance is carcass inspection at all federal and state inspected slaughter establishments. The other main sources of tuberculosis detection are testing animals before interstate movement and during disease investigations. Live animal testing is performed with a screening test. If positive, the regulatory veterinarian will conduct a confirmatory test.
Can it be Treated?
Unfortunately, tuberculosis in livestock is not a treatable disease. When health officials find tuberculosis in a herd, it is managed by either depopulating the herd or by testing and removing reactor animals.
