| Yellowstone Bison Slaughter
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Article 4/27/06 |
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| Test
results overstated brucellosis rate in elk
By Scott McMillion, Bozeman Daily Chronicle
4/27/06 |
Finally,
there's some good news about brucellosis in Montana
wildlife.
For the past two years, wildlife managers
have been increasingly concerned by what appeared to be
a spike in the number of Madison Valley elk that tested
positive for exposure to brucellosis.
Now, it turns out the concerns were
based on misleading test results and the brucellosis rate
in that large migratory elk herd hasn't grown after all,
the Montana Department of Fish, Wildlife and Parks announced
Wednesday.
Researchers have known for about 20
years that a small proportion of the Madison elk herd
- less than 2 percent - has tested positive for exposure
to brucellosis.
However, beginning in 2004, blood tests
showed that number jumping to almost 7 percent.
Then, blood from elk killed in the Pioneer
Mountains, a considerable distance to the west, also began
testing positive for brucellosis.
The news alarmed cattlemen concerned
about the health of their beef herds, and posed a vexing
question for wildlife managers: Why, after years of stability,
should the brucellosis rate take an upward spike?
So researchers began looking at their
laboratory work, and resubmitted some of their samples
for new tests using a lab method called the Western Blot
test.
And that's where they found the answers.
They learned the standard field tests
they'd been using sometimes showed a positive result for
brucellosis when the real affliction affecting the
animal was something called yersinia, caused by a common
bacteria.
"It's one of those organisms that
occurs everywhere," said Mark Atkinson, a wildlife
veterinarian for FWP. "If you look for it, you find
it."
Yersinia is a much less serious disease
than brucellosis. It has no apparent impacts on domestic
livestock, Atkinson said. Some strains of it can cause
painful diarrhea in humans, but that strain isn't the
one detected in the elk.
"This is good news," Atkinson
said.
Plus, yersinia passes quickly. Brucellosis in
animals is considered incurable.
Atkinson added that it's unlikely any
of the elk that tested positive for the disease were actually
infected at the time they were sampled. Rather, the test
detected antibodies, which means the animal had been exposed
to the bacteria, and its immune system reacted accordingly,
creating antibodies.
Montana state veterinarian Tom Linfield
agreed that the announcement is good news, although limited.
A lower exposure rate among elk means
fewer animals potentially exposing cattle, he said, but
it does not eliminate the risk.
"I guess the relative risk is lower,
but it doesn't eliminate the risk," he said. "It's
still important that no one gets complacent about it."
The states of Wyoming and Idaho have
lost their brucellosis-free status for their cattle herds.
Exposures to infected elk have been blamed for outbreaks
in those states.
Testing of Montana elk will continue,
both by hunters who gather blood samples and by researchers
catching radio-collared animals. In the future, any positive
samples will be retested to determine whether the reaction
was caused by brucellosis or yersinia.
The last major reservoir of brucellosis in
the United States is in the wildlife in and near Yellowstone
National Park. Fear of the disease is the basis for Montana's
controversial bison management policies.
Unfortunately, the revelation about
yersinia in elk is unlikely to have any impacts on bison management,
Atkinson said.
Brucellosis is well documented
in the park's bison herd. And while it's possible
that some bison also carry yersinia, that doesn't
change the bison situation, Atkinson said.
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