Sequential study of lymph node and splenic aspirates during Theileria parva infection in calves.

The development of Theileria parva infection in calves with partially exteriorised spleens was studied. Macroschizont infected cells were detected in the spleen and prescapular lymph node on the same day following inoculation of stabilate in front of the ear, indicating a haematogenous dissemination of the parasite. Macroschizont infection reached a peak on day 14 in the lymph nodes and in the spleen. The time to the appearance of of piroplasms and the development of parasitaemia were similar in the peripheral blood and in the spleen. The packed cell volume and total while blood cell counts from peripheral blood and splenic aspirates both showed similar changes. There was a marked leucopenia, beginning from the onset of the febrile response, and a mild terminal anaemia. The exteriorisation of the spleen caused little distress or change in the calves and provides a useful technique of monitoring splenic responses during the course of disease.