Acute spotted fever rickettsiosis among febrile patients, Cameroon

Abstract

Although potential arthropod vectors are abundant in Cameroon, acute febrile illnesses are rarely evaluated for arboviral or rickettsial infections. Serum samples from 234 acutely febrile patients at clinics in Tiko and Buea, Cameroon, were examined for antibodies to Rickettsia africae and African alphaviruses and flaviviruses. These serum samples did not contain antibodies against typhoid, and blood malarial parasites were not detected. Serum samples of 32% contained immunoglobulin M antibodies reactive with R. africae by immunofluorescence assay and were reactive with outer membrane proteins A and B of R. africae by immunoblotting. These findings established a diagnosis of acute rickettsiosis, most likely African tick-bite fever. Hemagglutination inhibition testing of the serum samples also detected antibodies to Chikungunya virus (47%) and flaviviruses (47%). High prevalence of antibodies to arboviruses may represent a major, previously unrecognized public health problem in an area where endemic malaria and typhoid fever have been the principal diagnostic considerations.

Figure 1

Location of townships in South West Province of Cameroon where samples were obtained.

Figure 2

Immunoblot of Rickettsia africae antigens with R. africae–positive and –negative patient serum samples. Lanes 1–3: R. africae–positive patients’ serum samples; lanes 4–5: R. africae–negative patients’ serum samples; lane 6: anti–OmpA monoclonal antibody; lane 7: anti–OmpB monoclonal antibody.