Natural and acquired resistance to Trypanosoma vivax in cattle.

Zebu x European (Z x E) crossbred cattle suffered a more severe course of disease than Boran cattle when infected with Trypanosoma vivax (Likoni) by Glossina morsitans. All Z x E animals in this study required Berenil treatment while all Borans self-cured the infection without treatment. The more severe disease in Z x E animals was characterized by longer periods of patent infection and fever, more severe anaemia and greater likelihood of haemorrhage. Cattle previously infected and cured with Berenil showed resistance and self-cured challenge infections. After self-cure cattle remained immune to tsetse fly challenge with the homologous trypanosome stock for long periods. Immunity induced by infection and drug or self-cure appeared to be specific for the homologous stock, since cattle immune to T. vivax (Likoni) showed no resistance when challenged with stocks of T. vivax isolated in Lugala, Uganda or Galana, Kenya. Severe haemorrhages, most prominent in the digestive tract, were seen in some infected cattle before treatment.