A survey on the incidence of antibodies to Babesia bigemina and Babesia bovis in one to three year old calves at 274 localities in Zimbabwe revealed that B. bigemina occurred throughout the country together with its main vector, Boophilus decoloratus. The distribution of B. bovis followed closely that of its vector Boophilus microplus which is limited to the eastern part of the country. Enzootic stability for B. bigemina was recorded in most of the communal tribal areas where regular dipping of cattle had been interrupted for several years but was less common on commercial farms where regular dipping is practised. Enzootic stability for B. bovis was restricted to a few localities in communal areas and the parasite was rare on commercial farms.

The brown ear tick Rhipicephalus appendiculatus suppressed in vivo and in vitro immune responses in the rabbit. Humoral responses were suppressed during infestation; however, suppression was transient and was unrelated to previous exposure of hosts to similar tick infestations. Immune suppression was caused by putative lymphocytotoxic factor(s) in tick salivary secretions as evidenced by in vitro lymphocytotoxicity assays. In an identical study of Rhipicephalus zambeziensis, a closely related rhipicephalid, the immune response was not suppressed, indicating that immune suppression is not common to the genus Rhipicephalus.

A survey on the incidence of antibodies to Anaplasma marginale in one- to three-year-old cattle was carried out in Zimbabwe using the capillary tube agglutination test. Antibodies were detected in all but one of 118 batches of sera collected from different localities throughout the country. There was no clear relationship between the frequency of occurrence of positive serological reactors, which was similar in both commercial and communal farming areas, and the incidence of clinical anaplasmosis. However, the highest numbers of cattle exhibiting positive reactions were generally recorded from the areas that were most heavily tick infested. There was evidence that wild ungulates may serve as reservoirs of infection as antibodies to A. marginale were detected in sera from buffalo (Syncerus caffer) and impala (Aepyceros melampus).

Successive infestation of the rabbit host by instars of the brown ear tick Rhipicephalus appendiculatus resulted in a progressive decline in engorgement and egg weights of adult instars and a reduction in percentage recovery of nymphs and larvae. Repetitive infestation with adults and larvae resulted in increased skin hypersensitivity reactions at the attachment site. Successive infestation with R. zambeziensis caused a more significant decline in engorgement and egg weights of adults than for R. appendiculatus. Percentage recoveries of larvae and nymphs were also significantly reduced. A cross-infestation study indicated that R. appendiculatus and R. zambeziensis share antigenic moieties.

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