DNR: Increase in TB cases is not a cause for alarm

Lansing – A slight increase in the prevalence of bovine
tuberculosis in white-tailed deer in the four-county bovine TB area
in northwest Lower Michigan is not by itself a warning that the
disease is returning, according to the DNR.

Instead, it tells researchers they may need to look for more
strategies for eradicating the disease, said Dr. Steve Schmitt, DNR
wildlife pathologist.

Schmitt recently told the Natural Resources Commission, which
oversees DNR policies and programs, that the incidence of TB within
Deer Management Unit 452, which includes Montmorency, Alpena,
Oscoda, and Alcona counties, rose from 1.4 percent in 2007 to 1.8
percent last year.

Last year, the DNR tested 16,200 deer for TB, with 36 testing
positive. Of those, 34 came from the four-county DMU 452, plus one
each from Presque Isle and Iosco counties.

Under the standards of statistics, though, the increase cannot
be called significant.

Just as polling results several percentage points apart can
sometimes be considered a tie, the relatively low number of animals
tested and testing positive makes small changes less telling.

“From 2002 through 2008, statistically there was no trend – not
up, not down,” Schmitt told Michigan Outdoor News in a phone
interview. “But from 1995 – when we had a lot higher prevalence,
almost 5 percent – through 2008, there is a significant declining
trend.”

Longer-term views are needed in assessing the disease, Schmitt
said, because “TB doesn’t transmit among animals quickly, and
because infected animals live a long time.

“It’s now stabilized,” he said of the virtual flat spot in
whitetail infection, “and that’s a little concerning to us.”

It’s an indication, he said, that the “broad-brush” strategies
used so far against bovine TB in deer – a ban on feeding and
baiting, and a reduction of the herd through expanded hunter
harvest – may have accomplished all they can.

“Plus, it did look like we had a jump in (bait-ban) compliance
in the seven-county TB area,” Schmitt said. “That could be due to a
perception that it’s now a more level playing field,” with baiting
banned throughout the Lower Peninsula last year, “that people
figured if others had to do it (hunt without bait), they would,
too.”

That’s good, he said, but if the disease prevalence didn’t show
a big change from that better compliance, it might mean deer
numbers are creeping upward again.

Additional strategies?

“We’re always working with other agencies and private companies
to develop better blood tests. We’re also working with the USDA
with vaccines,” Schmitt said.

Bovine TB vaccines are available, he said, but studies are
necessary to see if the live bacteria vaccines, shed from
vaccinated deer, would then vaccinate other deer.

Another question is whether they’d be picked up by cattle which,
while not contracting the disease, would falsely test positive for
it using current blood tests.

So, is the DNR aiming to eradicate bovine TB?

“Obviously, we need to aim for that,” Schmitt said. “Whether
that can be achieved with the strategies we have – the baiting ban
and reductions in deer numbers – nobody knows.”

Answers may come from a TB computer model now being developed,
with Michigan researchers adapting a program used in New Zealand to
track brushtail opossums, he said.

That program might provide answers to questions such as, “What
is the density below which this disease can’t sustain itself?”

The answer and others could help guide management, Schmitt
said.

Leave a Reply

Your email address will not be published. Required fields are marked *