Isolation and transmission of an unidentified Babesia sp. infective for cattle.

Engorged adult female ticks submitted from farms in South Africa were routinely screened for protozoan parasites by examination of haemolymph smears. An unidentified Babesia sp. was found in Hyalomma marginatum rufipes and its transmission to susceptible cattle was achieved both biologically (tick feeding) and mechanically (injection of infected blood). Attempts to transmit this species to susceptible rabbits and a horse using similar methods did not produce evidence of infection. This Babesia sp. was of low pathogenicity, even in splenectomized cattle. Morphologically, intra-erythrocytic piroplasms and merozoites in tick haemolymph resembled other bovine Babesia spp. in many respects. Although it could be classified as a large Babesia, it was intermediate in size between the other species.