Immunosuppression in bovine trypanosomiasis: response of cattle infected with Trypanosoma congolense to foot-and-mouth disease vaccination and subsequent live virus challenge.

The primary and secondary antibody responses to foot-and-mouth disease virus vaccine were examined in cattle infected with Trypanosoma congolense and the response of some of these animals to live foot-and-mouth disease virus challenge was assessed. Infected groups of cattle had rather lower antibody responses than uninfected control cattle after primary vaccination but the antibody titres were not significantly depressed until after secondary vaccination. These levels remained depressed for the duration of the experiment, ie, 183 days. Trypanocidal therapy with diminazene aceturate of infected cattle at the time of vaccination did not significantly improve the antibody response to primary vaccination. Their subsequent response to live virus challenge was somewhat equivocal in that the number of animals protected was not significantly different in comparison to the untreated infected and uninfected controls. It was concluded that trypanosome-infected cattle do not produce optimal responses to foot-and-mouth disease vaccination. Nevertheless, the antibody titres are generally above those considered adequate to confer 95 per cent protection against needle challenge.