East Coast fever; its transmission by ticks in Kenya Colony

Abstract

1. Investigations into some of the problems associated with African East Coast fever and its vectors have been undertaken: and although these are, as yet, incomplete we consider them of sufficient interest to warrant their publication at this stage.2. The present position regarding the distribution of certain tick species in relation to East Coast fever in Kenya is briefly reviewed; and outbreaks of what may be peculiar forms of the disease in sporadic areas are mentioned.3. It is thought that the passage of Theileria parva through different species of ticks might throw light on some sporadic outbreaks of the disease and on the peculiar character of some of the cases encountered.4. Transmission by nymphae and adults of Rhipicephalus appendiculatus, by adults of R. evertsi and R. simus is confirmed. Experiments with R. sanguineus, R. pulchellus and Amblyomma variegatum were negative.5. Exposure of infective nymphae of Rhipicephalus appendiculatus to different degrees and conditions of temperature prove that the ticks remain infective after being subjected to 4–6° C., and 8–10° C. for 1, 2 and 3 weeks. Exposure to different alternating temperatures for similar periods had no effect on the virulence of the parasite. The ticks exposed to warm temperatures (35–38° C,) did not survive to the same extent as those exposed to cold temperatures. Ticks that survived for 1 week transmitted the disease.6. Animals that ultimately recover from artificial infection may show a mild thermal reaction during the short course of the disease without showing typical clinical symptoms. In such cases diagnosis is frequently difficult, and Koch's bodies may be rare.7. The association of Hyalomma spp. with many different diseases is briefly dealt with; and it is shown that Hyalomma impressum near planum P. Sch. is capable of transmitting East Coast fever in the nymphal and the adult stages after the larvae and nymphae respectively have fed on an infected animal. The parasite does not pass through the egg. H. impressum near planum is common in most parts of Kenya Colony.