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Journal of Clinical Microbiology, Oct 1995, 2710-2714, Vol 33, No. 10
LA Magnarelli, KC Stafford 3rd, TN Mather, MT Yeh, KD Horn and JS Dumler
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 (blood cell),
rickettsia-like organisms. Hemolymph obtained from these ticks was analyzed
by direct and indirect fluorescent antibody (FA) staining methods with dog,
horse, or human sera containing antibodies to Ehrlichia canis, Ehrlichia
equi, or Rickettsia rickettsii. Of the 693 nymphal and adult Amblyomma
americanum, Dermacentor variabilis, Ixodes scapularis, and Ixodes pacificus
ticks tested with dog anti-E. canis antiserum, 209 (32.5%) contained
hemocytic bacteria. The prevalence of infected ticks varied greatly with
species and locale. In parallel tests of duplicate hemolymph preparations
from adult I. scapularis ticks, the hemocytic organisms reacted positively
with E. canis and/or E. equi antisera, including sera from persons who had
granulocytic ehrlichiosis. In separate PCR analyses, DNA of the agent of
human granulocytic ehrlichiosis was detected in 59 (50.0%) of 118 adult and
in 1 of 2 nymphal I. scapularis ticks tested from Connecticut. There was no
evidence of Ehrlichia chaffeensis DNA in these ticks. In indirect FA tests
of hemolymph for spotted fever group rickettsiae, the overall prevalence of
infection was less than 4%. Specificity tests of antigens and antisera used
in these studies revealed no cross- reactivity between E. canis and E. equi
or between any of the ehrlichial reagents and those of R. rickettsii. The
geographic distribution of hemocytic microorganisms with shared antigens to
Ehrlichia species or spotted fever group rickettsiae is widespread.
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Hemocytic rickettsia-like organisms in ticks: serologic reactivity with antisera to Ehrlichiae and detection of DNA of agent of human granulocytic ehrlichiosis by PCR
Department of Entomology, Connecticut Agricultural Experiment Station, New Haven 06504, USA.
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