Field-oriented trial of the Chinese Brucella suis strain 2 vaccine on sheep and goats in Libya.

The Chinese Brucella suis S2 vaccine was studied in a flock of sheep and goats in field conditions. The locally-produced vaccine was orally administered in the form of a drench to 446 ewes, 50 lambs and 20 adult goats. After vaccination, abortion and excretion of the vaccine strain in vaginal discharges or in milk did not occur. Serological tests became positive in 92% of animals at 4 wk post-vaccination and declined to near nil after 1 yr. The protection conferred by the vaccine against a double virulent B melitensis conjunctival challenge which infected 10/10 control ewes was on average 53% in ewes (32/60) and 71% in goats (5/7). Abortion rates were respectively 100% (7/7) in control ewes versus 44% (25/57) and 28% (2/7) in vaccinated ewes and goats. The vaccine was thus found to be safe, antigenic and reasonably protective against the challenge dose used.