Case of TB in cattle prompts deer testing
By Tim Spielman
St. Paul - The discovery of bovine tuberculosis in a cattle herd in northwestern Minnesota has prompted the state DNR to announce deer testing will take place in Roseau County this fall to see if area whitetails contracted the respiratory disease.
Mike DonCarlos, DNR wildlife program manager, said the exact area and the target number of deer to be tested hadn't yet been determined.
"What's clear is our goal - to determine if it's been transmitted to white-tailed deer, and if it has, how far it's gone and the infection rate," he said. "The first step is to find it, to determine if it has or has not gotten into the deer herd."
DonCarlos said bovine TB is a contagious bacterial disease that's found in cattle, but can be transmitted to other mammals, including deer and humans. It's a chronic, slowly spreading disease that doesn't spread easily. Bovine TB has never in the past been found in Minnesota deer.
Interaction between deer and cattle on the 5,000-acre cattle farm likely occurred, he said. Whether the disease was transmitted or not must be determined.
The cost of testing is unknown, DonCarlos said, because the agency hasn't decided what type of test will be performed and how many animals will be tested. Funding will come from a DNR account dedicated for wildlife health issues - the same fund that provided money for chronic wasting disease testing the past few years.
"We don't expect it (TB testing) to be costly, and the money is there," DonCarlos said.
The testing won't occur on the scale of that done for chronic wasting disease during the past few years. The DNR's Jason Abraham said since 2002, about 28,000 deer have been tested for CWD in all areas of the state. None have tested positive.
According to the DNR, bovine TB has been a rare occurrence in white-tailed deer and hasn't persisted in wild deer populations. Prior to 1994, only eight cases had been documented in wild deer in North America. However, since that time the disease has persisted in deer in several Michigan counties, possibly due to high deer densities and the prevalence of artificial feeding, the DNR's press release states.
The DNR recommends hunters and others follow a few simple rules regarding disease in wild animals.
"Baiting and feeding concentrate wild deer, which may increase the spread of diseases, such as bovine tuberculosis," DonCarlos said in a DNR statement. "Baiting is illegal in Minnesota, and the DNR discourages placing feed for wild animals."
Thorough cooking of the meat destroys the bacteria. Hunters should use gloves when field dressing deer to prevent disease exposure.
"This shouldn't change anyone's plans to hunt deer in northwestern Minnesota this fall," DonCarlos said. "With the proper precautions, hunters can safely field dress and enjoy their venison."
The Michigan experience
The area of concern in Michigan has been a four- to five-county area in the northeastern Lower Peninsula. Bovine TB was discovered in deer there 10 years ago, and testing of deer and liberal harvest continue today, though testing in 2004 showed "much progress had been made toward eradication of bovine TB in the wildlife population," according to the Michigan DNR.
The Michigan department tested more than 15,000 hunter-harvested deer last year, and 28 animals turned up bovine TB-positive. The prevalence rate in Deer Management Unit 452 - the area hit hardest by bovine TB - was 1.7 percent, a decrease of 65 percent since 1995.
The DNR in Michigan also is working to develop an accurate TB blood test and an effective TB vaccine, the agency states in a news release.
"Clearly, we are winning important battles in the war on bovine TB," said Stephen Schmitt, a Michigan DNR official.
Bill Parker, editor of Michigan Outdoor News, ON's sister publication, said the TB "scare" first hit the state hard, but currently CWD causes more concern, even though that disease hasn't been found in the state's wild deer herd.
"It was the first big scare, a really big thing that affected hunting," he said of TB. The discovery of TB led to the prohibition of baiting in the TB core area (baiting is illegal in Minnesota) and restrictions outside that area.
Also, the DNR in Michigan has been offering over-the-counter sales of deer tags to aggressively reduce the herd size in that area, Parker said. The department believes it has reduced the deer herd by 50 percent; some hunters in the area believe the herd's been reduced even more than that, he said.
Currently, he said the department's plan is to "stay the course" by continuing to put harvest pressure on the herd and keeping bait out of the picture. The rationale is that baiting and feeding concentrate deer, making nose-to-nose contact more likely and increasing the chances of disease spread.
Parker said the prevalence rate has dropped from a high of more than 5 percent testing positive for TB in the core area to less than 2 percent. In the outlying area, the prevalence rate has decreased from just over 2 percent to less than 1 percent.
"There's more concern now about CWD, and we don't even have that, that we know of," he said.
The Roseau herd
Not since the 1970s has the state had a case of bovine TB in a cattle herd. At that time, the state had to be "TB-free" for five years to be considered free of the disease by the U.S. Department of Agriculture, said Malissa Fritz, communications director for the state Board of Animal Health. That status returned in 1976.
But earlier this month, a USDA veterinarian detected suspicious lesions in a 5-year-old cow during routine slaughter surveillance. The cow was traced back to northern Minnesota using a "back tag" placed on the cow prior to being sold for slaughter. The Rouseau County herd, which numbered nearly 1,000 animals, was quarantined, tested, and an investigation initiated, according to the BAH.
Fritz said officials conducted a "whole-herd" test, which included 568 animals from the Roseau herd. Of those tested, biologists were particularly interested in the results from 21 of them, she said. Those were tested at the University of Minnesota Diagnostics Laboratory, and 18 tested positive for bovine TB.
"That number told us we had an infected herd," Fritz said.
Once the USDA and the producer work out an agreeable price during the indemnity process, the herd will be "depopulated," she said. Currently, state and federal officials are investigating where the cattle from the Roseau herd came from, and perhaps where they've gone. Further, three herds that had "fence line" contact with the infected herd also will be "whole-herd" tested for the disease.
Officials also are now discussing how long it will be before the Roseau farm is "cleared" - when they believe the bacteria has been eliminated from the farm site.