African tick bite fever

Abstract

A 13-year-old boy presented with a 2-day history of fever, malaise, headache, and myalgia. He had recently returned from safari in the Zambezi Valley, Zimbabwe, where he sustained bites from both ticks and mosquitoes while hunting wildebeest. On examination, the patient had a temperature of 39°C. Many cutaneous eschars were noted over his back, groin, and arms (fi gure), with tender regional lymphadenopathy. Three sets of blood cultures and thick and thin fi lms were negative. Haematological and biochemical investigations were all normal. A clinical diagnosis of African tick bite fever was made. Treatment with doxycycline was commenced and followed by a rapid recovery. Acute serology for African tick bite fever was negative but anti-rickettsial IgM was positive in convalescence. The child remains well more than 1 year after presentation. African tick bite fever is a rickettsial spotted fever, the causative organism being identifi ed as Rickettsia africae in 1992. The symptoms are non-specifi c and include fever, malaise, myalgia, and neck pain. The characteristic inoculation eschars consist of a central black crust surrounded by a red halo. The eschars are often multiple and associated with regional lymphadenopathy. Rapid response to doxycycline is anecdotally reported. Diagnosis is by serology, with PCR available as a research tool. Although the infection is usually mild, with no fatalities reported, it may be responsible for 26% of fever in travellers returning from sub-Saharan Africa. This high incidence requires that African tick bite fever be included in the diff erential diagnosis of all febrile children returning from the savannah of southern Africa. Lancet Infect Dis 2006; 6: 750