Spotted fever group rickettsiae in immature and adult ticks (Acari: Ixodidae) from a focus of Rocky Mountain spotted fever in Connecticut

Immature and adult ixodid ticks were collected during 1983 and 1984 in Newtown, Connecticut, an area endemic for Rocky Mountain spotted fever (RMSF), to determine prevalence of infection by spotted fever group (SFG) rickettsiae. Direct fluorescent-antibody (FA) staining revealed SFG organisms in 6 (1.8%) of 332 Dermacentor variabilis larvae, 5 (7.8%) of 64 D. variabilis nymphs, and in 2 (40%) of 5 Ixodes cookei nymphs removed from small- and medium-sized mammals. Hemolymph tests detected rickettsia-like organisms in 15 (8.8%) of 170 D. variabilis adults; 8 specimens retested by direct FA were negative. In contrast, hemocytes from 5 (8.6%) of 58 Ixodes texanus females contained organisms that stained positively in both hemolymph and direct FA tests. An indirect microimmunofluorescence test identified specific antibodies to Rickettsia rickettsii, the etiologic agent of RMSF, in serum samples from a chipmunk, raccoons, and white-footed mice. Results indicate that immature or adult ticks of at least three species may be involved in the maintenance and transmission of SFG rickettsiae at Newtown.