Our patient had a confirmed case of ATBF secondary to R africae infection, which was evident from tissue culture isolation and polymerase chain reaction analysis of swab material obtained from eschar sites, both of which yielded a positive result for R africae. The traveler’s negative serologic status might be due to his early exposure to doxycycline or to the 4-week delay in R africae seroconversion; his serum was collected only 3 weeks after the tick bites.
Clinical signs also aid in making the diagnosis of ATBF and distinguishing R conorii from R africae infection. Because of the aggressive hunting nature of the tick carrying R africae, they are associated with multiple eschars and tend to affect groups of multiple people, especially in rural areas.4,5 In contrast, ticks carrying R conorii yield a single eschar due to their passive style of infecting a host and because they favor a single host within urban areas.5 Both infections exhibit a maculopapular or papulovesicular rash and are accompanied by fatigue, headache, and myalgia, though ATBF tends to present with a milder rash than MSF.
Infection with either R conorii or R africae responds to tetracyclines, quinolones, and macrolides.10,12
African tick-bite fever is becoming more common, which should encourage clinicians to become familiar with the disease. Less than 2 decades ago, ATBF virtually was unknown outside of Zimbabwe, Botswana, Tanzania, Zambia, and Kenya, where it is endemic. However, after the abolition of apartheid in the 1990s, international tourism in southern Africa increased 6-fold.13 African tick-bite fever is now one of the most common rickettsial infections in Africa.7 In addition to diagnosing ATBF and managing infected patients, clinicians can help prevent ATBF in individuals who travel to endemic areas by recommending commercial topical insect repellents containing at least 19.5% N,N-diethyl-meta-toluamide (DEET).14