Experimental studies on the efficacy of T1 sr and T1/44 vaccine strains of <em>Mycoplasma mycoides</em> subspecies mycoides (small colony) against a field isolate causing contagious bovine pleuropneumonia in Kenya - Effect of a revaccination
H. O. Wesonga | F. Thiaucourt
Contagious bovine pleuropneumonia (CBPP) is an important disease of cattle causing serious losses to the livestock industry in Africa. It is controlled primarily through vaccination. However, recent observations in the field indicate that the vaccine in current use failed to protect cattle in the face of outbreaks causing concern to the veterinary authorities of affected countries. A field trial was carried out to determine the causes for vaccine failure. T1/44 and T1sr vaccine strains of Mycoplasma mycoides subsp. mycoides (small colony) were used to vaccinate a group of 40 cattle per strain. Half of these cattle were challenged at three months and the other half at 15 months following vaccination, respectively. Half of the cattle used in the second trial were revaccinated one year after the primary vaccination. A dose of 107 mycoplasmas per milliliter was used in primary as well as secondary vaccinations. In the first challenge (at three months post the primary vaccination), the efficacy was 68.2 and 59% for T1sr and T1/44 vaccines, respectively. In the second challenge, the efficacy was 80.5 and 95.5% for T1sr and T1/44 vaccines, respectively, in cattle vaccinated twice, while in cattle vaccinated once and challenged at 15 months post primary vaccination the efficacy was 28.7 and 78.2% for T1sr and T1/44, respectively. These results confirm what had been obtained in previous trials but they also bring valuable new information. They show that a single vaccination, whatever the strain used, at the minimum required dose does not give satisfactory protection and that full protection can only be achieved by revaccination. Consequences for future vaccine trials and research needs are discussed.
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