Fever and Vesicular Rash in a Traveler Returning from South Africa

Abstract

Figure 1. Vesiculated lesion on the right leg Diagnosis: African tick-bite fever with a vesicular rash. The geographical history, the incubation period, and the presence of a typical inoculation lesion, or eschar, on the right leg (figure 1) were suggestive of a rickettsial infection. The patient was treated with doxycycline (200 mg for the first dose, then 100 mg once per day for 1 week). The antimicrobial therapy was continued when the skin eruption appeared, and the fever and skin eruption disappeared within a week. Levels of IgM and IgG antibodies to Rickettsia africae were determined by indirect immunofluorescence; in acute-phase serum, their titers were 1:16 and 0, respectively, and in convalescent-phase serum, their titers were 1:32 and 1:128, respectively. Because of known cross-reactivity between Rickettsia conorii and R. af-ricae, cross-adsorption and Western blot assays were performed (by D.R.). After adsorption of serum samples with R. conorii, there remained 1 band of 120 kDa representing R. africae an-tigen but no bands representing R. conorii antigen, whereas after adsorption with R. africae, results were negative for both antigens. This finding confirmed that the infection was caused by R. africae. African tick-bite fever is caused by R. africae and transmitted by ticks of the genus Amblyomma. In contrast to the vectors of Mediterranean spotted fever (caused by R. conorii and transmitted by ticks of the genus Rhipicephalus) and Rocky Mountain spotted fever (caused by R. rickettsii and transmitted by ticks of the genus Dermacentor), Amblyomma species are not host-specific and readily feed on humans. African tick-bite fever has been termed a "spotless" rick-ettsiosis, in contrast to Mediterranean spotted fever (also known as "fièvre boutonneuse"). However, there are several recent reports of rash in patients with African tick-bite fever [1, 2, 4]. After a short period of fever, myalgia, headache, and fatigue, almost half of patients develop a maculopapular or vesicular rash (51% and 45%, respectively) [5] (figure 2). Patients often have multiple, characteristic inoculation es-chars, or so-called "taches noir" [3]; lymphangitis; and regional lymphadenopathy [6]. Infections frequently occur in clusters; the diagnosis of African tick-bite fever was also made