A Babesia sp. was recently observed in Hyalomma marginatum rufipes and found to be transmissible to bovines. Further observations were carried out on this parasite and a study made of the morphology of stages in both erythrocytes and tick haemolymph. Apart from Babesia divergens intra-erythrocytic parasites were not readily distinguishable from bovine Babesia spp. Merozoites in tick haemolymph morphologically resembled those of Babesia bigemina, but they were significantly larger. This Babesia sp. proved to be highly infective for adult H. m. rufipes, with transmission taking place transovarially and next generation nymphae and adults transmitting the infection.
Features of the infection were its very low pathogenicity, even in splenectomized animals, and the tendency of parasitized erythrocytes to accumulate in capillaries.
Serologically, this species could be differentiated from Babesia bigemina, B. divergens, B. bovis and B. major. A serological survey of 25 farms showed a wide distribution of this species in South Africa and its high rate of transmission on most properties. It was concluded that this is a true but hitherto undescribed bovine Babesia sp. and the name Babesia occultans n. sp. is proposed.
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