Michigan continues battle against bovine tuberculosis
With more than two decades of studying and testing white-tailed deer for bovine tuberculosis under its belt, Michigan has become a leader for its research and expertise on managing the contagious disease.
There are several types of tuberculosis, but bovine tuberculosis (bTB) can infect the widest variety of animals and is what wildlife managers have been trying to eradicate from white-tailed deer in Michigan.
Although originating and typically occurring in cattle, bTB can infect nearly any mammal, including humans. Bovine TB is caused by the bacterium Mycobacterium bovis (M. bovis), which is part of the Mycobacterium tuberculosis complex.
“This disease is contagious and can be debilitating to deer. Severely infected animals can struggle to even breathe,” said Kelly Straka, DNR state wildlife veterinarian. “By not eradicating this in the herd, we risk the spread of the disease to new areas of Michigan and into our wild elk herd.”
Bovine TB is spread primarily through the exchange of respiratory secretions and saliva between infected and uninfected animals. This transmission can happen when animals are in close contact with each other.
Bacteria released into the air through coughing and sneezing can spread the disease when inhaled by uninfected animals. In addition, food items contaminated with the saliva of an infected animal can transmit bTB to uninfected animals when they eat the contaminated feed. This is the primary way that cattle and deer infect each other.
Michigan detected TB in the early years
Bovine tuberculosis is a chronic disease that can take years to develop. The strains of bTB now present in Michigan are not native to North America, but were brought here by human movement of infected cattle from Great Britain in the 1700s and 1800s.
In the 1920s, nearly a third of cattle in Alpena and Alcona counties tested positive for bTB. In 1975, a single hunter-harvested white-tailed deer in Alcona County was found positive for bTB. At that time, it was thought that bTB couldn’t sustain itself in wild deer.
Nearly 20 years passed before a hunter harvested Michigan’s second bTB-positive deer in Alpena County in 1994.
Since 1995, Michigan has been testing white-tailed deer for bovine tuberculosis year-round. Michigan has the longest-running continuous wildlife TB surveillance program in the world.
To date, nearly 900 of over 230,000 deer tested in Michigan have tested positive for bovine tuberculosis. Seventy-eight percent of these TB-positive deer have been from a core area — Deer Management Unit 452 — in the northeastern part of Michigan’s Lower Peninsula, where the counties of Montmorency, Alpena, Oscoda and Alcona meet.
However, bTB is endemic (i.e. self-sustaining at a low level) across all four of those counties, and in Presque Isle County. Ninety-seven percent of all the bTB-positive deer ever found have come from that five-county endemic area. Antrim, Cheboygan, Crawford, Emmet, Iosco, Mecosta, Osceola, Otsego, Roscommon and Shiawassee counties also have had deer test positive for bTB.
An effective disease-management tool
Hunting has been the primary tool for managing bovine tuberculosis in Michigan.
“The majority (93 percent) of land in DMU 452 is private and is known locally as ‘the club country,’” said Brian Mastenbrook, DNR wildlife field operations manager. “One of the primary reasons to own this land and be club members is to hunt deer. We work with as many of the clubs as we can on all aspects of deer herd management.
“We appreciate the cooperation of the club members and all the other hunters throughout DMU 452. Hunters have been responsible for reducing the disease prevalence by over 50 percent between the mid-1990s and now.”
Recently, the Michigan Hunting Access Program expanded into the northern Lower Peninsula specifically to open more land to deer hunting. The program leases private lands and makes those lands available to anyone with a valid hunting license.
Working together for success
Despite many efforts over the years, bovine tuberculosis has not gone away. In 2016, 29 deer and six cattle herds tested positive for the disease.
“Since the first TB-affected cattle herd was discovered in June 1998, there have been a total of 69 cattle herds, five feedlots and three privately owned cervid facilities found to be infected with the Michigan strain of bovine TB,” said Rick Smith, assistant state veterinarian.
The agencies responsible for managing deer and cattle populations include the Michigan DNR, Michigan Department of Agriculture and Rural Development and U.S. Department of Agriculture. Together these agencies are working collaboratively on new approaches to combat the disease.
Michiganders called to action
The DNR is urging hunters to submit heads for testing from all deer harvested in the following counties: Alcona, Alpena, Cheboygan, Crawford, Huron, Iosco, Lake, Mecosta, Montmorency, Newaygo, Ogemaw, Osceola, Oscoda, Otsego, Presque Isle and Roscommon. The testing is offered free of charge.
Infected deer may not show chest lesions. Deer carcasses with chest lesions suspected to be evidence of bovine TB should be submitted from anywhere in the state. A list of DNR deer check stations is available at www.michigan.gov/deer.
DNR wildlife managers encourage anyone who sees a deer with this type of infection to contact the DNR so the carcass can be examined. Hunters may check their deer or elk TB lab results at www.michigan.gov/dnrlab.
There are signs of bovine tuberculosis hunters may observe when field-dressing a deer.
Lymph nodes in the animal’s head usually show infection first and, as the disease progresses, lesions may begin to develop on the surface of the lungs and chest cavity. In severely infected deer, lesions can sometimes be found throughout the animal’s entire body.
Deer with severe TB may have tan or yellow lumps lining the chest wall and in the lung tissue. Deer showing this type of infection should be submitted to the DNR for laboratory testing.
For more information on bovine tuberculosis, visit www.michigan.gov/emergingdiseases