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The spread of brucellosis is perceived as the main problem preventing bison from being outside Yellowstone National Park year-round. Eliminating the disease is an obvious solution but an impossible one, a U.S. Department of Agriculture researcher said Tuesday in Bozeman.

The partners of the Interagency Bison Management Plan and about 75 biologists, livestock producers, wildlife advocates and tribal representatives listened to Agricultural Research Service scientist Steve Olsen describe the problems with trying to control Brucella abortus, the brucellosis bacteria that causes cattle, bison and elk to abort their young.

“Vaccination alone will never eradicate brucellosis,” Olsen said. “We don’t have a vaccination in veterinarian or human medicine that will provide 100 percent protection from a pathogen.”

The IBMP is considering the possibility of darting bison with vaccine if they go outside the park without being tested for brucellosis. The partners made no decisions Tuesday.

Olsen’s information would help the partners determine if vaccinating bison would be effective in keeping cattle from becoming infected with brucellosis, in spite of the fact that elk have been responsible for all recent cases of brucellosis in cattle.

“I don’t think you can consider brucellosis without considering the elk problem,” Olsen said.

Little of what Olsen said indicated vaccination would be a cut-and-dried solution.

First, each of the 10 Brucella species infects select hosts and behaves differently within a group of hosts, so unlike some bacteria, they should not be treated the same by scientists or governments, Olsen said.

Olsen said studying the disease in mice won’t provide information about bison infection, and studying bison is expensive. So bison-specific data are limited.

Plus cattle, bison and elk all react differently to infection, Olsen said. The wild species, bison and elk, can better tolerate infection, probably because they evolved to exist with it, Olsen said.

In a study, infected cattle aborted 54 percent of their calves compared to 16 percent of bison.

Those animals that didn’t abort probably fought off the disease, Olsen said, but no one has studied whether those animals continued to carry the bacteria, which could cause future abortions.

That’s because inside an animal, Brucella bacteria are stealthy, Olsen said.

Bacteria gets in through an animal’s mucus membranes in the nose or mouth, and while just one bacterium can cause infection, a huge number can invade the body before the immune system is triggered.

“With E. coli, animals get a fever with 50 but we’re putting in 10 million Brucella to get our responses,” Olsen said.

Because of that, a blood test cannot always show whether an exposed animal has been infected.

Four Brucella species can infect humans, but symptoms are most severe with the species that infects goats – B. melitensis, Olsen said. That’s why the U.S. Department of Homeland Security has classified all Brucella species as possible bioterrorism weapons.

That severely limits research into bison vaccinations, even though the Brucella species that infects cattle poses a low threat to humans.

“To do research, we need to get it off the select agent list, so we have to give them science,” Olsen said. “It’s not going to work to tell them it’s costing a lot of money – they see Brucella as a bio-weapon.”

Even if research opens up, finding a new vaccine will be difficult because all the easy solutions were found long ago, Olsen said.

“We have a pretty good vaccine for cattle, the vaccine for bison is moderately effective and no vaccine for elk and then we have the issues with delivery,” Olsen said. “The vaccines won’t eradicate the disease so it’s a complex problem.”

Laura Lundquist can be reached at 582-2836 or Follow her on Twitter at @llundquist.

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