Rickettsia africae, a tick-borne pathogen in travelers to sub-Saharan Africa.

Background: African tick-bite fever occurs after contact with ticks that ca rry Rickettsia africae and that parasitize cattle and game. Sporadic report s suggest that this infection has specific clinical and epidemiologic featu res. Methods: We studied patients who were tested for a rickettsial disease afte r returning from a visit to Africa or Guadeloupe. To assess the value of th e microimmunofluorescence assay, Western blotting, and cross-adsorption ass ays, we compared the results of these tests in 39 patients in whom African tick-bite fever had been confirmed by the polymerase-chain-reaction assay, cell culture, or both; 50 patients with documented R. conorii infection; an d 50 blood donors. These diagnostic criteria were then applied to 376 addit ional patients who had returned from southern Africa and 2 who had returned from Guadeloupe and whose serum was being tested for rickettsial disease. Results: In the 39 patients with direct evidence of R. africae infection, t he combination of microimmunofluorescence assay, Western blotting, and cros s-adsorption assays showing antibodies specific for R. africae had a sensit ivity of 0.56; however, each test had a positive predictive value and a spe cificity of 1.0. An additional 80 patients were found to have an R. africae infection on the basis of these serologic criteria. Infections with R. afr icae were acquired by visitors to 11 African countries and Guadeloupe. The illness was generally mild and was characterized by a rash in 46 percent of the patients; the rash was usually maculopapular or vesicular and rarely p urpuric. Ninety-five percent of patients had an inoculation eschar or escha rs, and 54 percent of these patients had multiple eschars, a finding that i s unusual in patients with rickettsial infection. Conclusions: In this series, R. africae was the cause of nearly all cases o f tick-bite rickettsiosis in patients who became ill after a trip to sub-Sa haran Africa. (N Engl J Med 2001;344:1504-10.) Copyright (C) 2001 Massachus etts Medical Society.