Contagious bovine pleuropneumonia vaccines: the need for improvements.

Contagious bovine pleuropneumonia (CBPP) vaccines are routinely used only in Africa. The vaccines are usually produced from one of two strains (T1/44 and KH3J), each of which has a streptomycin-resistant variant. The necessity for a 'master seed strain' is evident. At least one manufacturer in Africa produces a broth culture vaccine, while others produce a freeze-dried product. A standardised manufacturing protocol needs to be developed, together with in-process and final product quality control procedures. Some CBPP vaccine manufacturing procedures do not allow sufficient leeway for the execution of typical quality control practices. For example, it is difficult to perform batch testing on broth culture vaccine, as the vaccine is produced in its final container. Quality control test results from the Pan African Veterinary Vaccine Centre (PANVAC) are analysed in terms of causes of batch failure and indicators for process development. Taking potency as an example, most vaccine batches tested by PANVAC pass only at the limit of the OIE minimum requirement of 10(7) colony-forming units per dose. To improve the titre of the vaccine, it will be necessary to modify the manufacturing process, either by increasing mycoplasma yield during the culture phase or by minimising losses during downstream processes, especially freeze-drying. Data on inactivated vaccines are scarce. Duration of the immunity achieved with live CBPP vaccines is relatively short, in comparison with other live vaccines. Data may be required on the molecular basis of virulence and immunogenicity, as well as on the molecular immunology of CBPP, to enable the development of improved vaccines.