Hemocytic rickettsia-like organisms inIxodes scapularis: transovarial and transstadial transmission

Abstract

Unengorged, host-seeking female Ixodes scapularis were collected from the northeastern United States (Rhode Island and Massachusetts) in April 1992. Hemolymph preparations from F1males and females were tested to determine if hemocytic rickettsia-like organisms, having shared antigens with ehrlichiae, are passed transovarially and transstadially. Fluorescein-labeled dog anti-Ehrlichia canis antiserum was used to detect infected hemocytes by means of direct fluorescent antibody staining methods. In duplicate tests of F1ticks, hemocytes from 25 males and 25 females were tested by indirect fluorescent antibody staining methods with antisera from two persons who had Rocky Mountain spotted fever. These hemolymph preparations were nonreactive, but those from cohorts of ticks reared from five infected females and tested with anti-E. canis antiserum contained rickettsia-like organisms in the cytoplasm of hemocytes. Thirty-four (54.8%) of 62 males and 71 (63.4%) of 112 females were positive. Prevalence of positive males among the five cohorts ranged from 18.8 to 80%, while results for females varied between 21.2 and 91.7%. The unidentified rickettsia-like hemocytic organisms, which have shared antigens with Ehrlichia species, are transmitted transovarially and transstadially in I. scapularis.