Immune depression in bovine trypanosomiasis: effects of acute and chronic Trypanosoma congolense and chronic Trypanosoma vivax infections on antibody response to Brucella abortus vaccine.

Cattle were vaccinated with Brucella abortus (S19) vaccine during acute (25 days) and chronic (25 weeks) Trypanosoma congolense and chronic Trypanosoma vivax (25 weeks) infections in order to determine the effect of such infections on the antibody response to the vaccine. It was found that the specific antibody responses of IgG1 and IgG2 sub-classes were profoundly depressed (80%) in both the acute and chronic infections with T. congolense. Whereas IgM antibody response was also profoundly depressed (90%) in cattle with the acute infection, it was only 50% depressed in those with chronic infection. There was no depression of IgG1, IgG2, or IgM in cattle infected with T. vivax. These animals, however, had no detectable parasitaemia at the time of vaccination and thereafter. These results suggest that during acute infection with T. congolense depressive mechanisms could be acting on the afferent arm of the immune response, namely, antigen recognition and/or processing.