Immunodepressive effects of trypanosomal infection in cattle immunized against contagious bovine pleuropneumonia.

Groups of cattle infected singly with Trypanosoma vivax and T. congolense and, with a combination of T. vivax and T. congolense, were vaccinated against contagious bovine pleuropneumonia (CBPP) 6 weeks before or after infection. All animals were revaccinated 12 weeks after primary vaccination. The primary antibody responses in cattle vaccinated 6 weeks after infection with T. vivax and a combination of T. vivax plus T. congolense were slightly depressed in contrast to other groups which were similar in their response to the control group. Although secondary antibody responses developed in all infected groups, with a delay in those infected with T. congolense, they did not reach the levels of the controls. In spite of the slight depression in antibody responses, however, 50% of the vaccinated trypanosomal animals contracted CBPP on exposure to experimental infection while the vaccinated controls were immune. It is suggested that the protective immunity to CBPP engendered by vaccination is impaired during infection with African trypanosomes and that the level of antibody response to CBPP vaccination in trypanosomal animals does not reflect the degree of immunodepression. The importance of trypanosomiasis control in ensuring success of vaccination campaigns against CBPP is discussed.