Control methods and thresholds of acceptability for antibrucella vaccines.

Protection against brucellosis involves both cellular and humoral effectors not yet fully appreciated. Living or killed vaccines can protect against the infection itself or only against abortion. For official controls, vaccines (or new procedures of vaccination) must first be characterized pharmacologically and tested for innocuity. Protection must be tested on natural hosts with a reference vaccine (S19 or Rev. 1) by the agreed method which reproduces the natural infection and measures immunity in toto. Control and vaccinated females are challenged by the conjunctival route at mid-pregnancy under standard conditions (strain, dose) to measure the resulting infection by bacteriological analysis of excretion at parturition and of infection in target organs at slaughter. Results are principally expressed by the infection rate which should be +/- 95% in the control group. In the new vaccine group the rate should be equivalent to, or lower than, the reference vaccine group. To be statistically valid, at least 30 animals per group are required. For routine controls, laboratory models using guinea pigs, not well standardized, inaccurate and expensive, have long been proposed. The mouse model, extensively studied and standardized, should now be preferred to the guinea pig model. In the mouse model, residual virulence of a living vaccine is estimated by the time required by 50% of the mice to eradicate the strain from their spleen (Recovery Time 50%). Immunogenicity is measured by the ability of mice to restrict their splenic infection after a virulent i.p. challenge at a dose (B. abortus 544; 2 x 10(5) cfu) chosen in order that all mice were still infected 15 days post challenge.(ABSTRACT TRUNCATED AT 250 WORDS)