Vaccine against brucellosis needs work.

Bison strike fear into the hearts of ranchers-not because these huge beasts sometimes charge people, but because many bison harbor the bacterium Brucella abortus. Ranchers worry that these bison may infect cattle herds with the bac- terium, which causes brucellosis. Cows with the disease have high abortion rates and lower than normal milk production. Widespread use of a live vaccine, B. abortus strain 19 (S19), has greatly reduced the incidence of brucellosis in cattle.

In bison, S19 is useless-it fails to provide sufficient immunity and causes abortions. Moreover, the picture for bison won't brighten anytime soon. Ran- chers have begun to use a new vaccine, B. abortus strain RB51 (SRB51), for their animals because tests can't distinguish cattle vaccinated with S19 from those infected naturally.

In one of the vaccine's first trials in bison, Mitchell V. Palmer of the U.S. Department of Agriculture's Agricultural Research Service in Ames, Iowa, and his colleagues gave the new vaccine to 10 pregnant animals.

Two of the bison aborted their fetuses, the researchers report in the November American Journal of Veterinary Research. That's fewer abortions than the old vaccine caused but much higher than healthy animals' normal rate. The authors conclude that "lower doses of SRB51 may be required for safe inoculation of pregnant bison."

Researchers have yet to determine whether the new vaccine makes bison immune. Bacteria from the vaccine survive in the aborted placenta, Palmer and his col- leagues note, so using the vaccine without reducing the abortion rate could lead to infections of cattle and other animals that inspect or eat the placenta.

Another attempt to solve the brucellosis problem failed this summer. A Senate bill that called for sterilizing or killing thousands of infected bison (SN: 3/23/96, p. 188) died in committee.