HEMOCYTIC RICKETTSIA-LIKE ORGANISMS IN TICKS - SEROLOGIC REACTIVITY WITH ANTISERA TO EHRLICHIAE AND DETECTION OF DNA OF AGENT OF HUMAN GRANULOCYTIC EHRLICHIOSIS BY PCR

Ixodid ticks were collected from Connecticut, Massachusetts, Missouri, Pennsylvania, Rhode Island, and British Columbia (Canada) during 1991 to 1994 to determine the prevalence of infection with hemocytic (bloo d cell), rickettsia-like organisms. Hemolymph obtained from these tick s was analyzed by direct and indirect fluorescent antibody (FA) staini ng methods with dog, horse, or human sera containing antibodies to Ehr lichia canis, Ehrlichia equi, or Rickettsia rickettsii. Of the 693 nym phal and adult Amblyomma americanum, Dermacentor variabilis, Ixodes sc apularis and Ixodes pacificus ticks tested with dog anti-E. canis anti serum, 209 (32.5%) contained hemocytic bacteria. The prevalence of inf ected ticks varied greatly with species and locale. In parallel tests of duplicate hemolymph preparations from adult I. scapularis ticks, th e hemocytic organisms reacted positively with a canis and/or E. equi a ntisera, including sera from persons who had granulocytic ehrlichiosis . In separate PCR analyses, DNA of the agent of human granulocytic ehr lichiosis was detected in 59 (50.0%) of 118 adult and in 1 of 2 nympha l I. scapularis ticks tested from Connecticut. There was no evidence o f Ehrlichia chaffeensis DNA in these ticks. In indirect FA tests of he molymph for spotted fever group rickettsiae, the overall prevalence of infection was less than 4%. Specificity tests of antigens and antiser a used in these studies revealed no cross-reactivity between E. canis and a equi or between any of the ehrlichial reagents and those of R. r ickettsii. The geographic distribution of hemocytic microorganisms wit h shared antigens to Ehrlichia species or spotted fever group ricketts iae is widespread.