East Coast fever as a cause of calf mortality in Zanzibar.

Crossbred and zebu calves at 4 to 5 months of age in an area where tick control was carried out showed little difference in mortality. Crossbred calves at 10 months of age had a mortality rate of 20% from all causes, 14% from East Coast fever. Serological results plus mortality studies showed that the survival rate of crossbred calves known to have been exposed to ECF was 57%. Serological results further showed that, in spite of tick exposure, only 26% of the crossbreds had seroconverted at 10.3 months of age while 15% zebus had positive titres.