Tick-Bite Fever (Tick Typhus) in Southern Africa

Abstract

Tick-bite fever or tick typhus occurring in southern Africa is a rickettsial disease caused by Rickettsia conorii var. pijperi transmitted by ixodid ticks. The infection passes from one generation of ticks through the eggs to the next. The larvae, nymphs and adults are potentially infective to man. The infection is transmitted through the bite during feeding. The bite mark develops into an inflamed red papule, the centre of which becomes necrotic and black to form the characteristic primary lesion. The regional lymph glands become enlarged and tender. Systemic signs include chills, muscle and joint pains, headache, and delirium in severe cases. In untreated cases, the fever typically lasts 10 days. In severe cases the patient may lapse into coma and on recovery may have defective speech. Other severely ill patients develop a hemorrhagic state which may be fatal. Diagnosis of tick-bite fever may be confirmed in the laboratory by the isolation and identification of the rickettsiae or by specific serological tests. The illness responds specifically to treatment with chloramphenicol and tetracycline antibiotics which usually results in a dramatic improvement after 48 h. The striped mouse Rhabdomys pumilio and the vlei rat Otomys irroratus may serve as reservoirs of infection. The domestic dog and the common black rat, Rattus rattus, may acquire the infection and may be important sources of infection to humans. Tick-bite fever may be avoided by avoiding contact with ticks. Protective vaccines have also been produced experimentally but are not in general use.