Seroprevalence of antibodies against spotted fever group rickettsia among dogs and humans in Okinawa, Japan.

We evaluated serum antibodies against Rickettsia japonica in 517 dogs (430 stray dogs and 87 pet dogs) and 164 humans in Okinawa, Japan, by indirect immunofluorescence assay. The seropositive rate in stray dogs was significantly higher than that in pet dogs (30.7 versus 4.6%, P<0.01). This high prevalence rate is attributed to the understandably frequent environmental exposure of stray dogs to tick infestation. Human samples obtained from Okinawa and Sapporo also showed a significant difference in seropositive antibody percentages (45.1 and 12.0%, respectively, P<0.01). This result suggests that there has been pre-exposure to spotted fever group rickettsia in humans in Okinawa.