BERKELEY -- A dispute as bitter as a Montana winter rages between ranchers and environmentalists over Yellowstone National Park bison and a disease called brucellosis, which can harm cattle. In a National Research Council report to be released this month, UC Berkeley and Iowa State University researchers aim to help settle the conflict with new studies and recommendations.

The report, "Brucellosis in the Greater Yellowstone Area," contains findings from Dale R. McCullough, professor of wildlife biology in the College of Natural Resources at the University of California, Berkeley, and Norman Cheville, chairman of the Department of Veterinary Pathology at Iowa State University. The report was released in draft form in December and is scheduled for final publication in late January.

Brucella abortus, the bacteria that causes brucellosis, arrived in North America with European cattle and appeared in Yellowstone bison in 1917. It can cause spontaneous abortion in cattle and other animals, and is transmitted primarily through reproductive fluids and nursing.

"Animals come into contact with products of abortion or infected birth tissues from normal births of infected mothers," said report co-author Dale McCullough. "They are behaviorally curious about abortion products particularly. It can be transmitted (to cattle) in other ways, but it is rare." Within the bison population, brucellosis is also spread from mother to young by milk.

Last winter was extremely harsh in Yellowstone and hundreds of bison died of starvation in the 2.2-million-acre park. Others left it in record numbers, searching for more available forage at lower elevations. Alarmed that some of the itinerant animals might be infected with brucellosis, Montana livestock officials killed nearly 1,100 of the bison.

Hoping to prevent a repeat of such drastic measures-and the ensuing public outcry-the U.S. Department of the Interior commissioned a National Research Council report to analyze the problem and suggest solutions.

"Bison always have been an important icon of the American West and wildness," said McCullough. "Yellowstone is just about the only place in the country where there remains a free-ranging population of the animals. Some of them have lineages that go back, uninterrupted, to the original stocks. People feel very strongly about these animals and their future."

Such passion was evident recently in a Montana courtroom, where a U.S. District Court Judge heard arguments brought by conservation groups to halt all bison killing. He refused to do so, though he did limit the slaughter to 100. If that number is reached, the judge ruled, another hearing must be held.

While at the highest there were 3,500 bison in and around Yellowstone National Park, up to 120,000 elk inhabit the area. According to the NRC report, the National Elk Refuge and 21 Wyoming elk feeding grounds south of Yellowstone National Park have high potential for brucellosis transmission. Eliminating these feeding grounds would greatly reduce brucellosis transmission, the report says, but this solution is unlikely given the elks' importance to hunters and tourists.

In Yellowstone this summer and fall, McCullough and Cheville heard presentations from scientists, ranchers and environmental groups. "Some claim the chance of bison infecting cattle is remote, and no management strategies are needed," McCullough says. "Others argue that any risk of transmission is unacceptable, and the disease must be eliminated from the wild."

Ranchers are particularly worried, he says, not just that the disease will be detected in their beef herds but that it will be detected in their states -- which could lead to cattle trading restrictions. At present, the USDA Animal and Plant Health Inspection Service (APHIS) has designated 37 states as brucellosis-free for cattle and bison. California, where brucellosis has been detected in the past, has recently regained its brucellosis-free status.

This winter has been mild in Yellowstone. No bison are known to have been shot. But McCullough and Cheville say their fate-and the fate of the area's elk and cattle-will rely on steps taken to manage them all.

"To make the Yellowstone Area brucellosis-free," the authors write, "the disease must be eradicated in all three species simultaneously. A lot more research is needed to determine whether and how such an ambitious goal can be met."

The disease in humans is called undulant fever. Though rare, it can cause illness, treatable by antibiotics, in people who drink unpasteurized milk or handle infected cows.

The report's major findings include:

• The threat of brucellosis spreading from Yellowstone wildlife to cattle is too small to measure, but the risk too great to ignore. Because bison tissue cultures are difficult to obtain and blood tests are imprecise, infection rates are poorly known. For now, animals testing positive in blood tests for antibodies to brucellosis should be assumed to be carrying the disease. Transmission rates also are unclear, because little controlled research has been done on transmission in wild, free-roaming animals.
  
• Though most cattle are now vaccinated against brucellosis, no proven vaccine exists for bison and elk. Until one is developed, bison will continue to be infected and can pose a risk to cattle. Research must continue on a vaccine for bison and elk.
  
• The U.S. Departments of Agriculture and Interior should work together to establish formal surveillance efforts to intensely monitor the behavior and movements of bison and elk in and around the park. Tracking must increase as the animals stray closer to the park's perimeter. Limiting cattle near the perimeter would reduce transmission, but is unlikely given vigorous opposition from ranchers and the presence of private land.
  
• Likely, the disease will not be eliminated from the Yellowstone area anytime soon. "Total eradication of brucellosis is more a statement of principle than a workable program at present," the authors write.