Preliminary studies by ELISA on the antigen and antibody dynamics in the early stages of experimental infections with Trypanosoma evansi in cattle

Six 6-month-old bulls were experimentally infected with five different isol ates of Trypanosoma evansi; two received the same isolate and the other fou r received different isolates. The parasitaemias and serum antigen levels w ere monitored regularly by the haematocrit centrifuge technique (HCT) and a ntigen-detection ELISA (Ag-ELISA), respectively. Trypanosomal antigen was d emonstrated by the Ag-ELISA by 10-14 days post inoculation in four cattle, while parasitaemias were first found to be positive in individual cattle ov er a longer period of time post inoculation (6-28 days). In two cattle, the Ag-ELISA values were also positive when the animals were found to harbour trypanosomes by the HCT and only turned negative 3 days after treatment, wh ile the ELISA values fluctuated during the experiment in another two bulls. The remaining two cattle never produced positive ELISA results despite pos itive parasitological results. The antibody titres in all six cattle starte d to rise around 10 days post inoculation and then stayed high throughout t he experiment. It was concluded that the Ag-ELISA would produce some false negative results in the early stages of T. evansi infection owing to variat ions in the balance of parasitaemia and antibody levels in the circulation, and in the pathogenicity of parasite strains.