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State finds bovine TB in 23 more white-tailed deer

Posted on April 25, 2013

Lansing — Twenty-three whitetails and four cattle herds found infected with bovine tuberculosis in 2012 and early ‘13 are reasons for continued vigilance against the respiratory disease. That was the message state veterinarians Steven Schmitt of the DNR, and Rick Smith, of the Department of Agriculture and Rural Development, had for  members of the state Natural Resources Commission at its April meeting in Lansing.

Michigan began aggressive testing for bovine TB in 1995 following a positive case of TB in a white-tailed deer killed by a hunter in Alpena County the previous year. Prior to that time, only eight wild deer had been reported with the disease across North America. The disease used to be relatively common in cattle, but today, Michigan and  California are the only two states in the country with TB in cattle.

“It is a very chronic disease. An animal can have lesions (internally) and live for months, even years. This is a big problem for us because it can spread the disease,” Schmitt told the commission.

He said high deer densities and concentrations of deer at feed sites are the main reasons TB has persisted in Michigan’s whitetails.

“We’ve had high deer numbers in northeast Michigan for 100 years, and we’ve had baiting and feeding in northeast Michigan for 100 years,” he said.

Scientists have tested 199,659 white-tailed deer in Michigan since 1994 for bovine TB, and 725 have tested positive. In 2012, state officials tested 4,716 deer and 23 were positive – 18 from Deer Management Unit 452, the core area of the TB outbreak. The rest were from surrounding counties. In fact, 99 percent of all the TB-positive deer have come from 11 counties in northeastern Michigan, according to Schmitt. None have been found in the Upper Peninsula or southern Lower.

“When we first started testing we didn’t know where it was, so we tested deer from all over the state,” Schmitt told the commission. “Now we focus our effort where we know it exists.”

Since testing began in ‘94, the prevalence rate of TB in free-ranging whitetails has dropped 55 percent in DMU 452 to 1.7 percent last year. In the five counties surrounding DMU 452, the prevalence rate hovers around 0.3 percent.

“We should be proud of that,” Schmitt said. “A lot of work and effort went into that.”

Also last year, TB testing of Michigan’s hunter-harvested elk resulted in one positive result. Since 1996, 2,984 elk have been tested and six have tested positive, five from Montmorency County and one from Presque Isle County.

“These are areas with high TB rates in deer,” Schmitt said. “Most likely they are sharing some common feeding sites with deer.”

The state’s strategy for dealing with TB in whitetails is to keep deer from concentrating at feeding sites and to reduce deer numbers below the estimated 100,000 that remain in the five-county TB zone.

Schmitt said baiting remains a problem, despite the practice being outlawed in the TB zone.

“To reduce the prevalence rate further, basically we have to reduce deer numbers below the 100,000 we have right now, but the public doesn’t want that and it is mostly private land,” Schmitt said. “Our TB models show that to eradicate the disease it would take doubling the buck and doe harvest for 15 years. If we get a modest reduction, maybe 10 percent, we could reduce the prevalence rate and that would reduce the rate of transmission to cattle. It’s still a very difficult situation.”

What makes the situation tough is the fact that area cattle herds continue to contract the disease, threatening the livelihoods of cattle farmers.

According to Smith, three cattle herds in Alpena County tested positive for the disease last year, and one in Saginaw County was confirmed in February, bringing the total number of herds affected by TB to 56.

In March, scientists confirmed that it was the Michigan strain of TB found in Saginaw County, ruling out the possibility that the disease was shipped in from outside the state. About 17 percent of that herd tested positive.

“We have the dubious distinction of having our own strain of TB,” Smith said.