Rickettsiae-infected ticks (acari: Ixodidae) and seropositive mammals at a focus for Rocky Mountain spotted fever in Connecticut, USA.

Abstract

Ticks and wild mammals were collected in 1980 and 1981 from Newtown, Connecticut, USA, an area where 6 persons probably acquired Rocky Mountain spotted fever (RMSF) during 1978–1981. Dermacentor variabilis , the American dog tick, parasitized a variety of small and medium-sized mammals but was most prevalent on White-footed Mice and Raccoons. It was the only tick found infected with hemocyte-associated, rickettsia-like organisms; of the 347 adults removed from hosts during 1980–1981, 50 (14.4%) were positive by the hemolymph test. Direct immunofluorescence tests confirmed spotted-fever group (SFG) rickettsiae in 16 (4.6%) specimens. The following mammals contained antibodies to SFG rickettsiae: Eastern Chipmunks, Gray Squirrels, Meadow Voles, Virginia Opossums, Raccoons, a Short-tailed Shrew, Striped Skunks, White-footed Mice, Woodchucks, and Woodland Jumping Mice. Serologic results support clinical histories of human RMSF cases, and combined with tick-infectivity data suggest continued rickettsial activity in this ecosystem.