CROSSPROTECTIVE IMMUNITY BETWEEN THE FLORIDA AND A ZIMBABWE STOCK OF ANAPLASMA-MARGINALE

Cattle immunised by infection with the Florida stock of Anaplasma marginale were protected against subsequent homologous challenge, as demonstrated by complete prevention of microscopically detectable parasitaemia. Identically immunised cattle were partially protected against challenge with the Norton, Zimbabwe stock of A. marginale as determined by the significant prolongation of the prepatent period, a significantly lower peak parasitaemia, and a significantly lower percentage drop in haemoglobin concentration when compared to non-immunised calves challenged identically. The partial protection induced by live Florida stock immunisation demonstrates that while protection-inducing epitopes are shared between the two stocks, induction of complete immunity against a Zimbabwe stock may require alternative presentation of Florida stock epitopes or inclusion of additional Zimbabwe stock epitopes in the immunogen.