Studies on immunity with three species of avian trypanosomes

The ability of three species of avian trypanosome, Trypanosoma corvi, T. bouffardi and T. everetti, to protect against heterologous and homologous challenge has been studied in susceptible birds. None protects against challenge with either or both of the other two species and mixed infections can be obtained experimentally. With T. bouffardi, both apparently sterile and premune states exist after initial infection and the host is immune to challenge with homologous strains; heterologous strains sometimes break this immunity and produce shorter, lower parasitaemias. T. everetti remains in the circulating blood for long periods at low levels and challenge doses with the homologous strain result in a slightly elevated parasitaemia for a few days. T. corvi produces a degree of immunity after the initial infection which usually results in a reduced second parasitaemic peak of shorter duration when birds are challenged with a homologous strain.