Brucellois, long the "boogey man" disease that ranchers have cited as the reason to keep Bison in bottled up, zoo-like and restricted habitat,,,,,, has never been documented being transmitted from bison to cattle...................This disease is alien to the USA and like so many "exotic" pests and pathogens, came from Europe................Elk have a higher likelihood transmitting the disease to catte(causes cattle to abort pregnancies) and yet Elk are allowed to range across the landscape......................Bison penned up because Ranchers fear that they will outcompete cattle and take over the grasslands they historically occupied?

New West Feature

Can Bison Actually Transmit Brucellosis to Cattle?

In a laboratory, it's happened before. In a natural setting, it's a more remote possibility. But the fear of roaming buffalo infecting a herd of cattle still frightens ranchers.

By Kate Whittle
A microscopic bacterium called Brucellus abortus, or brucellosis, is one of the biggest factors in bison management. The disease is a major concern for the cattle industry and is a primary reason why allowing Yellowstone bison to roam freely in Montana is so controversial. But it's still unclear whether brucellosis-infected bison pose a risk to cattle.
Brucellosis can cause cattle, elk and bison to abort their pregnancies. The disease was brought to the U.S. by cattle and spread to bison in 1917 when bison were corralled with a herd of cattle in Yellowstone Park.
Brucellosis can wreak havoc on a rancher's herd, and a state's beef exports are restricted if an outbreak leads U.S. Department of Agriculture inspectors to take away the state's brucellosis-free status. This happened in 2007 when elk passed the disease to cattle near Yellowstone National Park and caused two brucellosis outbreaks. Montana wasn't declared brucellois-free until 2009. Another brucellosis outbreak could seriously hurt Montana's billion-dollar cattle industry.
Brucellosis is carried by both males and females, but the disease is most commonly spread by females leaving behind afterbirth or aborted calves infected with the bacterium. If another animal sniffs or licks at that infected matter, it can become infected itself. Yellowstone Park officials estimate about half of the park's bison herd carries brucellosis, but the disease doesn't affect bison as severely as cattle.
But do Yellowstone bison pose a threat to Montana cattle? In a 1990 study from Texas A&M [PDF], researchers infected a cow by feeding it brucellosis-tainted material. While it's been proven in a lab, in the decades since cattle first passed the disease to bison, there's been no documented case of bison transmitting the disease to cattle outside a laboratory. 
Stephany Seay is a spokesperson for the Buffalo Field Campaign, a non-profit group that advocates for allowing bison to roam freely and has strongly criticized Yellowstone National Park's and the state of Montana's bison management. "The whole brucellosis argument is simply a theory," she said. Since most cattle are pastured and fed hay for the winter, they aren't likely to come in contact with bison, she says. "For buffalo that may be infected with brucellosis, if it was suffering the symptoms, it would miscarry in winter, [when] there's absolutely no cows on the landscape."
Elk also carry brucellosis but are allowed to move freely—even though elk were the suspected culprits in each of the cattle brucellosis outbreaks during the past decade, Seay says. A 2009 study published in Yellowstone Science found that elk may be more likely to spread brucellosis to cattle.
Seay believes the talk about brucellosis masks the real reason ranchers want bison managed. "This war on buffalo is about grass," she said. "Buffalo restoration is viewed by the livestock industry as a threat to cattle ranching."
Errol Rice, vice president of the Montana Stockgrower's Association says ranchers just want to ensure the epidemiology of brucellosis is well understood. "Our point of view is not founded upon hate for bison, or to reign supreme on the landscape, or prevent competition for grass," he said.  The Stockgrowers Association wants to see more brucellosis research, and vaccines developed for bison, Rice said. "Ranchers aren't really in the position to start talking about potential bison relocation until we get a better handle on the disease situation," he said.
Keith Aune, who recently retired as Chief of Wildlife Research at Montana Fish, Wildlife and Parks, said it's not a question of whether bison can transmit the disease to cattle, but whether it's likely.  "There's the probability that an infection occurs, that the infection becomes a fully fledged disease, that the disease becomes an abortion, that the abortion is left behind, that the bacteria will last long enough and some other animal will come along and ingest enough to become infected," he said. "Think about all those probabilities."  On the other hand, Aune is about to publish a study that found brucellosis can survive outside a host for up to 90 days, depending on the temperature. Whether that happens often remains to be seen.  Aune believes people sometimes wrongly perceive that wild animals are disease-ridden. "I think the fear from the rancher's perspective is real, but an artifact of not understanding the whole story," he said.  But Aune believes caution is in order. "The fact that something hasn't happened doesn't make a good case for 'It can't happen,'" he said. "We need to work on preventing those conditions from allowing it to happen. That's where the debate needs to go."