Epidemiology and Clinical Characteristics of Human Rickettsial Infections Detected in Nigeria: Discovery of a Significant Contributor to Acute Febrile Illness.

introductionRickettsial diseases are transmitted by arthropods and characterized by nonspecific febrile illness. Despite evidence of Rickettsia spp. in animals and vectors in Nigeria, human infection has not previously been documented to the best of our knowledge. Most clinicians lack awareness about these diseases. The burden of rickettsiosis in Nigeria is unknown.

methodsThe Surveillance of Acute Febrile Illness Aetiologiesin Nigeria study was a facility-based surveillance study designed to identify pathogens causing acute fever. Whole blood specimens from patients with undifferentiated fever were tested using a TaqMan Array Card, a polymerase chain reaction assay including Rickettsia spp., and an enzyme-linked immunosorbent assay for Rickettsia spp. immunoglobulin G and immunoglobulin M. Demographic, clinical, and outcome data were collected and analyzed.

resultsOf the 1200 patients enrolled, 26% tested positive for Rickettsia spp., via TaqMan Array Card and 28.7% via enzyme-linked immunosorbent assay. Common clinical characteristics were headache, nausea and vomiting, abdominal pain, muscle pain, and joint pain. Only 1.9% of the patients had a rash and none had an eschar. The overall case fatality rate was 4.2%, with significantly lower mortality in children compared to adults (0.8% vs 6.5%). Coinfections were detected in 36.2% of cases, most commonly with Plasmodium spp. (25%).

conclusionsThis study provides the first evidence of human rickettsial infection in humans in Nigeria, with a substantial prevalence among febrile patients. The absence of classic cutaneous signs such as rash or eschar may hinder clinical recognition. Rickettsial infection should be considered in the differential diagnosis of acute febrile illness in Nigeria, and molecular diagnostics should be expanded to improve detection and guide appropriate therapy.