Attempted transmission of Ehrlichia canis by Rhipicephalus sanguineus after passage in cell culture.
OBJECTIVE
To compare the transmissibility by the brown dog tick, Rhipicephalus sanguineus, of a recent isolate of Ehrlichia canis (Ebony) with that of another isolate (Oklahoma) that had been passaged in cell culture, and to assess the genetic similarity of the 2 isolates as reflected in the nucleotide (NT) sequence of 16S rDNA.


METHODS
13 healthy dogs of various ages and breeds.


METHODS
Larval and nymphal ticks were acquisition fed on acutely infected dogs, and, after molting, they were transmission fed as nymphs and adults, respectively, on Ehrlichia-naive dogs. All dogs were monitored daily by blood smear evaluation for evidence of parasitized leukocytes and by physical examination for clinical signs of ehrlichiosis. Serologic and hematologic values were measured weekly. Using a nested polymerase chain reaction, the 16S rDNA was amplified, and the NT sequence of the template DNA was determined.


RESULTS
The Ebony isolate of E canis was successfully transmitted to dogs by nymphal and adult ticks. In contrast, no ticks that fed on dogs harboring the cell-cultured isolate (Oklahoma) transmitted it to dogs. On the basis of 16S rDNA sequence, the 2 isolates were 99.9% similar, with only 1 NT difference.


CONCLUSIONS
These results reconfirm the vector potential of R sanguineus for E canis. Passage of the Oklahoma isolate of E canis in cell culture apparently adversely affected its transmissibility by ticks, raising the possibility that cell-cultured isolates of this rickettsia may lose their affinity for ticks. Determination of 16S rDNA sequence suggests minor strain variation within the species E canis.
Department of Infectious Diseases, College of Veterinary Medicine, Oklahoma State University, Stillwater 74078, USA.
J S
JS
Mathew
S A
SA
Ewing
R W
RW
Barker
J C
JC
Fox
J E
JE
Dawson
C K
CK
Warner
G L
GL
Murphy
K M
KM
Kocan
D000818:Animals; D001096:Arachnid Vectors / Q000382:microbiology; D001831:Body Temperature; D002478:Cells, Cultured; D004283:Dog Diseases / Q000635:transmission*; D004285:Dogs; D004536:Ehrlichia / Q000502:physiology*; D016873:Ehrlichiosis / Q000635:transmission* / Q000662:veterinary; D007074:Immunoglobulin G / Q000097:blood; D013987:Ticks / Q000382:microbiology*; D013997:Time Factors
D007074:Immunoglobulin G