Effects of killed Brucella abortus strain 45/20 vaccine on reindeer later challenge exposed with Brucella suis type 4.

Six seronegative pregnant reindeer (Rangifer tarandus L) were vaccinated with killed Brucella abortus strain 45/20 with added adjuvant. These were challenge exposed with B suis type 4 after 90 days; at the same time, 4 seronegative, nonvaccinated, pregnant reindeer (controls) were given the challenge inoculum. Humoral antibodies were detected in the vaccinated reindeer by postvaccination day 14. A marked increase in antibody levels also occurred after they were challenge exposed, but did not reach the levels observed in control reindeer which seroconverted within 8 days after they were given the challenge inoculum. One control reindeer aborted at 45 days after challenge exposure (at 165 days of a normal 225-day gestation period), and the fawn of another lived only a few days after delivery. Brucella suis type 4 was isolated from tissues of 3 of 4 control reindeer and of 2 of their fawns. All vaccinated reindeer gave birth to live fawns which were culture negative, although 1 fawn lived only a few days. Brucella suis type 4 was isolated from tissues of 1 vaccinated reindeer. Under the conditions of this experiment, killed B abortus 45/20 vaccine provided increased resistance to brucellosis.