Associated Press

YELLOWSTONE NATIONAL PARK, Wyo. (AP) - Researchers hope to perfect a new vaccination system that would allow them to shoot young bison with vaccine-laden "bullets" to help stop the spread of brucellosis in the park's bison herd.

The technique has shown promise in captive bison herds and on wild elk, but researchers say it also has problems that must be worked out before it could be used in the park.

"We've been working on this for quite a while," said Wayne Brewster, deputy director of Yellowstone National Park's Center for Resources. "We're getting closer, but we're not there yet. We still haven't got the silver bullet, so to speak."

Brucellosis is a disease that can cause bison and domestic cattle to abort their calves. It is estimated that as many as 20 percent of the park's wild bison are infected with the disease.

That has ranchers who graze cattle near the park concerned. Bison leave the park's boundaries every year and ranchers, especially those in Montana, fear bison could spread brucellosis to their cattle.

Under an existing management program between state and federal agencies, officials attempt to drive those bison that leave Yellowstone back into the park. In most cases, if they cannot be herded back into Yellowstone, the animals are captured, and those that test positive for brucellosis are slaughtered.

The management plan also requires the National Park Service to come up with a way to vaccinate all young bison in the park by 2004 or 2005.

"That's the goal, and we're working hard to get there," said Margaret Wild, a National Park Service wildlife veterinarian based in Denver.

Researchers have been attempting to develop a special vaccine "bullet," to inoculate the animals from a safe distance, but have run into a number of problems.

For one, existing air-powered rifles are not powerful enough to deliver the vaccine at the distance required for the wild bison, Brewster said.

Additionally, the bullet has been difficult to perfect. The idea was to encase a liquid vaccine in a biodegradable casing, but the liquid played havoc with the bullet's ballistics.

Researchers then tried to freeze-dry the vaccine first, but found out that process substantially reduced its effectiveness.

Researchers plan to meet later this month in Colorado to discuss progress on the new system and to go over other alternatives.

Wild said another promising idea is to shoot the bison with biodegradable needles or to place the vaccine in "treats" that could spread around the park in areas the bison forage.

So far, however, no oral vaccine has yet been developed, which means the vaccine bullet remains the best hope for now.

"It's the one approach that has the highest probability of coming online soonest," Brewster said.

Wild agrees. "In the long-term, an oral vaccine would be ideal. But we need something in the short-term, and we don't have time to wait," she said. "We need something safe and effective, and we need something quickly."
 

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