ANTIBODIES TO SPOTTED-FEVER GROUP RICKETTSIAE IN DOGS AND PREVALENCE OF INFECTED TICKS IN SOUTHERN CONNECTICUT

Abstract

Blood samples and ticks were obtained from dogs to assess canine exposure to spotted fever-group (SFG) rickettsiae during 1978-1980 in southern Connecticut, USA. Of the 1576 dog sera screened by microimmunofluorescence, 174 (11.0%) contained specific antibodies at titers .gtoreq. 1:64 against Rickettsia montana (n = 34), R. rickettsii (n = 31), R. rhipicephali (n = 19), or the unclassified 369-C rickettsia (n = 90). End points .gtoreq. 1:8192 to R. rickettsii and to R. rhipicephali were recorded for 6 and 3 sera, respectively. Seropositivity rates from southwestern and southeastern Connecticut were similar (.apprx. 11%), with positive sera obtained from each region in nearly all months of the investigation. Rates were between 10% for dogs 2-7 yr old and 14% for those .gtoreq. 8 yr. Eight of 629 Dermacentor variabilis, 1 of 18 Ixodes dammini, and 2 of 3 Amblyomma americanus were positive by direct immunofluorescence for SFG rickettsiae. Thirteen D. variabilis contained unidentified, long, bacillus-like organisms that differed from the short, ovoid (coccal) forms typical of the spotted-fever agent R. rickettsii. With the exposure to infected ticks and production of type-specific antibodies against at least 4 SFG antigens, dogs may serve as suitable enzootic or epizootic indicators of rickettsial activity.