Kinetics of Antibody Responses in Rickettsia africae and Rickettsia conorii Infections

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Abstract
African tick-bite fever, caused by Rickettsia africae , is the most common tick-borne rickettsiosis in sub-Saharan Africa. Mediterranean spotted fever due to Rickettsia conorii also occurs in the region but is more prevalent in Mediterranean countries. Using microimmunofluorescence, we compared the development of immunoglobulin G (IgG) and IgM titers in 48 patients with African tick-bite fever and 48 patients with Mediterranean spotted fever. Doxycycline treatment within 7 days from the onset of disease significantly prevented the development of antibodies to R. africae . In patients with African tick-bite fever, the median times to seroconversion with IgG and IgM were 28 and 25 days, respectively, after the onset of symptoms. These were significantly longer by a median of 6 days for IgG and 9 days for IgM than the times for seroconversion in patients with Mediterranean spotted fever ( P < 10 −2 ). We recommend that sera collected 4 weeks after the onset of signs of patients with suspected African tick-bite fever should be used for the definitive serological diagnosis of R. africae infections.