Michigan hunters, beware.

The U.S. Centers for Disease Control and Prevention has issued an advisory, warning that it is possible to catch a form of tuberculosis when field-dressing infected deer.

It's called M. bovis tuberculosis, and it's a form of the disease found mostly in cattle, elk and deer.

In Michigan, the deer in a four-county region of the northern Lower Peninsula: Alcona, Montmorency, Oscoda and Alpena are most likely to carry the infection. A small percentage of white-tailed deer from other parts of the state also have been found to carry the disease.

If a person has a cut or an open wound, blood and bacteria from an infected deer could enter the bloodstream, causing a human infection. It also may be transmitted when a human inhales aerosolized bacteria during the field-dressing process.

The case that was highlighted in the new CDC study was written by Dr. James Sunstrum, who works in the infectious diseases division of Beaumont Hospital in Dearborn, and Dr. Dan O'Brien, a wildlife veterinarian at the wildlife disease laboratory of the Michigan Department of Natural Resources.

It involved a 77-year-old hunter from the northern Lower Peninsula who had the disease in May 2017. He'd been hunting for two decades within the four-county zone where more deer are known to have the disease.

Whole-genome sequencing of the bacteria in his body showed that it matched a strain that had been identified in deer in Michigan, which, the CDC report said, suggests "that the patient was exposed to a circulating strain of M. bovis at some point through his hunting activities and had reactivation of infection as pulmonary disease in 2017."

The bacteria can cause active illness or a latent infection that remains dormant in the body until later in life, when stress or some other factor weakens the immune system and activates an infection.

That means someone could have tuberculosis, but not show symptoms for years, said Sunstrum.

"For most people, it will remain silent or latent, and can only be detected with a skin test or a blood test," he said. "But, if a person is becoming actively sick with TB, they usually have fevers for more than two weeks or three weeks, or coughing for two weeks or three weeks, and swollen lymph nodes."

Symptoms can also include night sweats, weight loss, abdominal pain and diarrhea. If untreated, a person can die of the disease, according to the CDC.

"TB is a very slow, gradual disease," Sunstrum said. "And, so, if something causes chronic signs of infection, that's when we might investigate. It is treatable and curable with antibiotics."

Two other cases of hunters acquiring this form of tuberculosis were recorded in 2002 and 2004 in Michigan. In each case, the patients had signs and symptoms of active disease and required medical treatment.

O'Brien and Sunstrum said hunters should take the following precautions:

Wear protective gloves when you field-dress deer.

Don't shoot or eat the meat of any animal that appears to be sick.

When you're field dressing a deer, look for signs of disease and have the head of the deer tested at any DNR field station. The hunting and trapping guide the DNR gives to every person who is issued a hunting license includes pictures of what disease looks like.

Cook deer meat to at least 165 degrees to kill tuberculosis bacteria and other pathogens.

The CDC didn't go so far as to recommend wearing a mask, however, during the field-dressing process.

"We don't recommend that at this point in time," O'Brien said. "The physicians in the group have speculated that that might be the route by which these hunters got infected, but we don't have any actual data to show that. In fact, when we've done some sampling of air inside deer carcasses in the past that had tuberculosis, we weren't able to actually detect any aerosols of the bacteria.

"That remains an open question and we don't really know. But, given the fact that we have had people harvesting deer in that part of the state for a very long time, and we have a relatively small number of people who've actually become infected and sick, that would suggest that this isn't a particularly easy disease to transmit to people."

The CDC advised targeted screening for tuberculosis among hunters, and any deer that tests positive for TB should not be eaten.

"For those folks that actually harvest a deer that tested positive for TB, we recommend to those folks that the deer not be consumed either by them or fed to animals," O'Brien said.

Although deer-to-human M. bovis tuberculosis infections are rare, there's still a risk.

"This is the only place in the United States where humans are getting TB when they come in contact with the infected deer, and this is the only place in the United States where wild deer are infected with TB on a significant basis," Sunstrum said.

Within the four-county higher-risk zone, the disease affects just 1.4% of deer. Of the 35,892 deer heads submitted statewide for disease testing to the Michigan DNR in 2018, only 26 were positive for M. bovis tuberculosis, O'Brien said.

"The risk of a hunter even harvesting a deer that is infected with TB goes down dramatically if you're not hunting in the northeast" part of the Lower Peninsula," said O'Brien. "It's theoretically possible. But we've been testing for over 20 years, and ... it's very unusual to see infected deer in outlying areas from that."

M. bovis tuberculosis used to be more common in humans when people drank unpasteurized milk from cows carrying the disease. But now, it accounts for less than 2% of the total number of cases of TB disease in the United States, according to the CDC.

Sunstrum urged hunters to take advantage of the free testing service at DNR field offices.

"The DNR has a very good surveillance system for deer hunters, where they can drop the deer head off at an DNR check stations all across Michigan," he said. "The DNR will mail a postcard back with a report on whether that deer had tuberculosis and they can also test for Chronic Wasting Disease."

For more information about deer hunting in Michigan, go to Michigan.gov/deer.

Contact Kristen Jordan Shamus: 313-222-5997 or kshamus@freepress.com. Follow her on Twitter @kristenshamus.