Comparative efficacy trial of two strains of vaccines T1/44 and T1sr against contagious bovine pleuropneumonia

Abstract

Contagious bovine pleuropneumonia is an infectious disease affecting cattle. It has acquired recently a growing importance in Africa. In the past, many countries had controled the disease or even eradicated it thanks to the use of two strains of live vaccines, T1/44 and a streptomycino-resistant variant T1sr. Recent vaccinal failures with the T1sr strains had cast doubts on the identity and the efficacy of this vaccinal strain. Since then its identity has been confirmed. It was therefore necessary to verify the efficacy in controlled conditions. The two strains were used at the minimum required dose, 107 mycoplasmas by vaccinal dose. The experimental reproduction of the disease was obtained by endobronchial intubation of 40 animals that served as “donor” to infect vaccinated as well as control animals by contact. Transmission occured readily and the mortality rate reached 40% among the control animals. Vaccinated animals died at a lower rate (p = 0,054) but the protection was only equal to 37% when considering the reduction of mortality. It is quite difficult to compare this result with older ones as many former trials were using vaccine doses with a higher content of mycoplasmas and were using a challenging strain isolated in Australia. The results obtained in this experiment pinpoint the partial protection that is afforded by a primovaccination at the minimum recommended dose. It calls for further research on more efficient vaccines and also for a better definition of the CBPP control strategies that should be urgently implemented.