The pathogenesis of anaemia in Theileria annulata infection.

Calves infected by a field strain of Theileria annulata developed severe anaemia, which was accompanied by bilirubinaemia and the appearance of free serum autohaemagglutinin antibodies. Animals infected with an agamogenous strain (lacking erythrocytic forms) also became anaemic. Anisocytosis appeared in all infected animals but regenerative anaemic lesions were observed only in those which survived the infection. In this group of animals anaemia was accompanied by bilirubinaemia and the development of free serum auto-haemagglutinin. In calves premune to theileriosis splenectomy resulted in a recrudescence of erythrocytic forms but no fever. Only mild anaemia and bilirubinaemia occurred in this group of animals in spite of the high level of parasitism. Tests failed to show any production of free serum auto-haemagglutinin. It is postulated that, in T annulata infection, erythrocytic forms as well as schizonts contribute to the anaemia although the role played by schizonts is greater. The involvement of an auto-immune reaction is proposed.