THE INABILITY OF A SOUTH AFRICAN BABESIA OVIS VACCINE STRAIN TO INFECT BOOPHILUS MICROPLUS

A strain of Babesia bovis that had been attenuated by rapid syringe passage through a series of 23 splenecto-mized calves was unable to infect its vector Boophilus microplus. An attempt to transmit the attenuated Austra-lian Babesia bigemina G strain with a South African strain of B. microplus was likewise unsuccessful. The epidemiological implication of these observations in terms of babesiosis control is discussed. INTRODUCfiON Bovine babesiosis is of economic importance in areas of the Republic of South Africa in which the 2 vector ticks Boophilus decoloratus and Boophilus micro-plus occur. The disease is controlled by the use of a blood vaccine containing both Babesia bigemina and Babesia bovis parasites. Progress has been made as far as the virulence of the current vaccine strains is concerned. The virulence of the B. bovis S strain was reduced through rapid needle pas-sage in splenectomized calves (De Vos, Bessenger & Fourie, 1982). Three slow needle eassages of a local B. bigemina strain in intact calves faded to show a reduc-tion in virulence and consequently the hi~hly passaged attenuated Australian B. bigemina G stram (Dalgliesh, Callow, Mellors & McGregor, 1981) was imported. Its efficacy as a possible vaccine strain was tested in the laboratory before it was incorporated into the Onderste-poort babesiosis vaccine (De Vos, Combrink & Bes-senger, 1982). Blood-passaged Babesia strains sho