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)