Epidemiology of Rocky Mountain spotted fever in Ohio, 1981: serologic evaluation of canines and rickettsial isolation from ticks associated with human case exposure sites.

A survey for the prevalence of Rocky Mountain spotted fever (RMSF) antibodies in dogs associated with confirmed human cases in Ohio was conducted during 1981. Twelve of 14 confirmed cases (85%) had a history of dog association prior to onset of RMSF. A total of 29 dogs were included in the study, with 16 dogs providing serum samples for antibody testing and the remainder providing tick samples. Serum samples tested by indirect microimmunofluorescence techniques revealed 12/16 dogs (75%) to be seropositive for Rickettsia rickettsii. A total of 310 ticks were collected from study dogs and the vegetation surrounding RMSF case exposure sites. Twenty-two (7.1%) of these ticks (all Dermacentor variabilis) were found to be infected with spotted fever group rickettsiae. Four ticks (1.3%) were infected with R. rickettsii, 13 (4.2%) with Rickettsia montana, and four (1.3%) with Rickettsia bellii. R. montana, a nonpathogen, was the only rickettsia found in dogs (antibodies) and ticks (isolation) associated with human cases in Southern Ohio.