TRANSMISSION OF ANAPLASMA-MARGINALE WITH ADULT BOOPHILUS-MICROPLUS TICKS FED AS NYMPHS ON CALVES WITH DIFFERENT LEVELS OF RICKETTSAEMIA

Nine splenectomised cakes were infested with dissimilar numbers of adult Boophilus microplus ticks 72 h after collection as engorged nymphs from three non splenectomised cakes with different levels of Anaplasma marginale rickettsaemia. Successful transmission of A. marginale appeared to be more dependent on the level of rickettsaemia of the donor cakes than on the number oi ticks attaching to the splenectomised calves, since infection was transmitted only when the rickettsaemia was 0.3 % or greater. Field transmission would thus depend on the rate of tick migration amongst susceptible hosts and the rickettsaemia level of cattle on which the licks led previously.