Tick infestations and tick-borne diseases in Zimbabwe Rhodesia.

The distribution of tick species in Zimbabwe Rhodesia is significantly influenced by land utilization practices. The most commonly occurring species in the over-grazed tribal areas is Boophilus decoloratus. By contrast, well-managed commercial farms and ranches support a wide range of tick species, the most important of which is Rhipicephalus appendiculatus. Until recently tick-borne diseases of cattle were efficiently controlled through dipping. The low incidence of disease was an important factor contributing to over-grazing in tribal areas. Between 1973 and 1978 political unrest resulted in a collapse of the dipping service in tribal areas. Populations of B. decoloratus built up and outbreaks of babesiosis and anaplasmosis occurred, normally between one and three years after the cessation of dipping. Reduced grazing pressure after the initial disease waves resulted in increased grass cover, allowing species such as R. appendiculatus and Amblyomma hebraeum to become re-established. Outbreaks of theileriosis and heartwater usually followed, decimating the already depleted herds. The heavy cattle mortality resulted from lack of immunity to tick-borne diseases, as a result of efficient disease control through dipping in previous years.