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Journal of Clinical Microbiology, Mar 1996, 664-670, Vol 34, No. 3
UG Munderloh, JE Madigan, JS Dumler, JL Goodman, SF Hayes, JE Barlough, CM Nelson and TJ Kurtti
The equine granulocytic ehrlichiosis agent, Ehrlichia equi, is closely
related or identical to the human granulocytic ehrlichiosis (HGE) agent.
Both are suspected of being transmitted by ticks. We have successfully
isolated E. equi in a cell line, IDE8, derived from a putative vector, the
tick Ixodes scapularis. Peripheral blood leukocytes from an experimentally
infected horse were inoculated onto IDE8 monolayers. Cultures were
incubated in a candle jar at 34 degrees C in tick cell culture medium with
NaHCO3 and an organic buffer [3-(N- morpholino)-propanesulfonic acid]
(MOPS). Within 2 weeks, infected cells were detected in Giemsa-stained
culture samples, and the organisms subsequently spread to uninfected cells
in the cultures. E. equi was passaged serially by transferring a portion of
an infected culture to new cell layers every 2 to 3 weeks. The identity of
the organisms was confirmed by PCR using oligonucleotide primers specific
for E. equi and the HGE agent and by immunocytology. Homologous equine
antibodies and human anti-HGE convalescent serum recognized E. equi grown
in tick cell culture. Electron microscopy revealed electron- lucent and
-dense ehrlichia-like forms developing within host cell endosomes. E. equi
passaged twice in tick cell culture retained infectivity and pathogenicity
for the equine host, as demonstrated by intravenous inoculation of a
suspension of infected tick cells and subsequent reisolation from
peripheral blood, in fulfillment of Koch's postulates. The horse developed
severe clinical signs, i.e., fever, inappetence, thrombocytopenia, icterus,
and limb edema, typical of granulocytic equine ehrlichiosis, within 1 week.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Isolation of the equine granulocytic ehrlichiosis agent, Ehrlichia equi, in tick cell culture
Department of Entomology, University of Minnesota, St. Paul 55108, USA. munde001@maroon.tc.umn.edu
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