The incidence of east coast fever in areas where the disease is endemic is associated with the common occurrence of the usual tick vector, Rhipicephalus appendiculatus. Outbreaks of the disease in other areas are sporadic or seasonal, and although, in many such instances, R. appendiculatus has been found either in isolated localities, or very sparsely distributed over the whole of an infected area, in other cases it has not been possible to collect even a single specimen of this tick. Collections of ticks from infected farms in these sporadic areas comprise such species as Boophilus spp., Rhipicephalus capensis, R. simus and R. evertsi or Hyalomma spp., Amblyomma spp., Rhipicephalus pulchellus and R. neavei.