Armed with dart guns and medical pellets（芯块，小球） , Agricultural Research Service (ARS) scientists are vaccinating（接种疫苗） bison（北美野牛） in and around Yellowstone National Park against brucellosis（普鲁氏菌病） . Researchers from the ARS National Animal Disease Center (NADC) in Ames, Iowa, are using a vaccine known as RB51. By vaccinating the wild bison, scientists hope to prevent the disease from spreading to nearby livestock. Currently, no cattle herds（畜群） in the U.S. are known to be infected, although some near Yellowstone have been sickened in the last decade.

Brucellosis, an incurable disease, can cause abortions in cattle, bison, elk（麋鹿） , and feral swine（野猪） . It can be transmitted to humans through contact with infected animals or consumption of unpasteurized（未经高温消毒的） dairy products. In humans, it's called undulant fever（波状热） , and causes severe flu-like symptoms.

Wildlife reservoirs of brucellosis in the United States include bison and elk (which carry Brucella abortus) and feral swine (which carry B. suis). The animals often come in contact with cattle, especially in winter when bison, elk, domestic livestock and swine are all foraging for the same food. B. suis can be transferred to farm animals or people.

Steven Olsen, a veterinary（兽医的） medical officer at NADC, has led the team on the bison vaccination study. During the project, researchers monitored animals to determine the natural course of B. abortus（流产胎） in female bison and their offspring（后代，子孙） . They found that in bison, the disease mimics the characteristics seen in cattle.

Brucellosis has been nearly eradicated（拜托，连根拔起） in the United States, mostly through cooperative federal and state programs dating back to the 1950s. But its continuing spread through wildlife in the Yellowstone area has rekindled concern among cattle producers. Currently, there is no eradication program for B. suis, according to Olsen.

Among the concerns of Olsen and his colleagues--microbiologists Fred Tatum and Betsy Bricker--is the difficulty in diferentiating between B. abortus and B. suis. This presents difficulties for federal officials because a national brucellosis eradication program only targets B. abortus.

In addition to the vaccination program carried out by ARS and other agencies, the National Park Service is conducting an environmental impact study on a proposal to spend $9 million for a new brucellosis eradication program in Yellowstone over the next 30 years.