Seroepidemiological and molecular investigation of spotted fever group rickettsiae andCoxiella burnetiiin Sao Tome Island: A One Health approach

Spotted fever group rickettsiae (SFGR) andCoxiella burnetiiare intracellular bacteria that cause potentially life-threatening tick-borne rickettsioses and Q fever respectively. Sao Tome and Principe (STP), small islands located in the Gulf of Guinea, recently experienced a dramatic reduction in the incidence of malaria owing to international collaborative efforts. However, unexplained febrile illnesses persist. A One Health approach was adopted to investigate exposure to SFGR andC. burnetiiin humans and examine the diversity of these bacteria in ticks parasitizing domestic ruminants. A cross-sectional human serological study was conducted in Agua Grande district in Sao Tome Island from January to March 2016, and ticks were collected from farmed domestic ruminants in 2012 and 2016. In total, 240 individuals varying in age were randomly screened for exposure to SFGR andC. burnetiiby indirect immunofluorescence assay. Twenty of 240 individuals (8.3%) were seropositive for SFGR (4 forRickettsia africaeand 16 forR. conorii) and 16 (6.7%) were seropositive forC. burnetii.Amblyomma astrionwere collected exclusively in 2012, as wereA. variegatumin 2016 andRickettsiaspp. were detected in 22/42 (52.4%) and 49/60 (81.7%) respectively. Sequence analysis of multiple gene targets fromRickettsiaspp. detected in ticks suggests the presence of a single divergentR. africaestrain (Sao Tome). While no ticks were found positive forC. burnetii,Coxiella-like endosymbionts were detected in nearly all ticks. This is the first study in STP to provide serological evidence in humans of SFGR andC. burnetiiand additional molecular evidence in ticks for SFGR, which may be responsible for some of the unexplained febrile illnesses that persist despite the control of malaria. Future epidemiological studies are needed to confirm the occurrence and risk factors associated with SFG rickettsioses and Q fever in both humans and animals.