Incidence and some ecological aspects of avian trypanosomes in Czechoslovakia

A total of 1 874 birds belonging to 99 species was investigated on the presence of trypanosomes in Czechoslovakia, using the method of blood smears and cultivation from peripheral blood (PEN method) and autopsies with subsequent cultivation from the bone marrow. Apart from a single finding in owls, the trypanosomes were detected only in passerines which represent the majority of birds investigated (1 518 specimens belonging to 66 species). Except for sparrows, in which trypanosomes were present very rarely, they were abundant practically in all bird families represented by a sufficient number of specimens. Autopsies showed that trypanosomes occurred on the average in 23.6% of passerines. Throughout the year their presence in peripheral blood of birds ranged from a peak in June (29% of positive passerines after PEN method) to their absence in the winter months. There were differences in the incidence of trypanosomes in birds coming from localities with different biotopes. No essential difference was found in their incidence in migratory and non migratory birds. In birds several years old the incidence of trypanosomes was higher than in younger birds. Repeated investigations of ringed birds recaptured point out long-lasting infections with avian trypanosomes. A considerable correlation between the incidence of trypanosomes and that of Leucocytozoon, Haemoproteus and microfilariae indicates that avian trypanosomes are probably transmitted by blackflies (Simuliidae), biting midges (Ceratopogonidae) and louse flies (Hippoboscidae).