Rocky mountain spotted fever in Connecticut: human cases, spotted-fever group rickettsiae in ticks, and antibodies in mammals

Abstract

Three parameters were used in 1976 and 1977 to assess the status of Rocky Mountain spotted fever (RMSF) in Connecticut--compilation and review of clinical data on suspected human cases for the 13-year period 1965--1977, examination of tick tissues for spotted fever-group rickettsiae by the hemolymph test and direct immunofluorescence, and analyses of mammalian sera for antibodies against Rickettsia rickettsii. There were six presumptive RMSF cases which probably originated in Connecticut. Four of these cases occurred in areas where the American dog tick, Dermacentor variabilis, abounds. A total of 2994 ticks were examined by the hemolymph test. Rickettsia-like organisms were observed in 67 (2.9%) of 2330 D. variabilis and two (0.6%) of 351 Ixodes sp. near scapularis. Fewer than one-half of these organisms stained positively with spotted fever-group conjugate. Microagglutination tests on 1093 mammalian sera indicated that eight (16%) of 49 raccoons, 14 (2.6%) of 549 white-tailed deer, eight (1.7%) of 470 white-footed mice, and one of two gray squirrels had agglutinins in titers greater than or equal to 1:8 against R. rickettsii. Spotted fever-group rickettsiae are present at low frequency in inland as well as coastal regions of Connecticut.