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 adu lt 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 appe ared to be more dependent on the level of rickettsaemia of the donor c akes than on the number oi ticks attaching to the splenectomised calve s, since infection was transmitted only when the rickettsaemia was 0.3 % or greater. Field transmission would thus depend on the rate of tic k migration amongst susceptible hosts and the rickettsaemia level of c attle on which the licks led previously.