Efficacy trials with tissue-culture grown, inactivated vaccines against chlamydial abortion in sheep.

Vaccines containing inactivated, semi-purified antigen of ovine abortifacient Chlamydia psittaci were prepared from tissue-culture grown harvests of two strains. These were evaluated for efficacy against experimentally reproduced enzootic abortion of ewes (EAE), the protection index (PI) of each vaccine being calculated from three variables. Trial 1 tested the adjuvants Marcol 52/Arlacel A, ISCOM matrix, Novasomes and Alhydrogel, each administered with a total antigen dose of 4 micrograms chlamydial protein (cp), against challenge with the two homologous vaccine strains. The first three formulations yielded PIs of 39-42%, while that of Alhydrogel was 23%. Marked granuloma and/or abscess formation occurred in the Marcol 52/Arlacel A group but in none of the others, and only this group seroconverted following vaccination. In Trial 2, ISCOM matrix containing 16 micrograms cp per dose was administered once or twice. Two challenges were used, one involving the two vaccine strains and the other these two strains plus five others, but no significant differences were seen between them. The double dose schedule, which was better than the single dose and also several Novasomes formulations tested concurrently, gave PIs of 64 and 77% against the two challenges (combined value 71.5%). Trial 3 studied duration of immunity over two lambing seasons using three different administration schedules of 16 micrograms cp in ISCOM matrix, namely single dose in year 1, single dose in year 2 (Group 1), double dose then booster (Group 2), and double dose without booster (Group 3). PIs against the homologous bivalent challenge were 79-80% for Groups 1 and 3 and 91% for Group 2.(ABSTRACT TRUNCATED AT 250 WORDS)