Evaluation of an attenuated strain of Ehrlichia canis as a vaccine for canine monocytic ehrlichiosis

Nir Rudoler, Gad Baneth, Osnat Eyal, Michael van Straten, Shimon Harrus*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Canine monocytic ehrlichiosis is an important tick-borne disease worldwide. No commercial vaccine for the disease is currently available and tick control is the main preventive measure against the disease. The aim of this study was to evaluate the potential of a multi-passaged attenuated strain of Ehrlichia canis to serve as a vaccine for canine monocytic ehrlichiosis, and to assess the use of azithromycin in the treatment of acute ehrlichiosis. Twelve beagle dogs were divided into 3 groups of 4 dogs. Groups 1 and 2 were inoculated (vaccinated) with an attenuated strain of E. canis (#611A) twice or once, respectively. The third group consisted of naïve dogs which served as controls. All 3 groups were challenged with a wild virulent strain of E. canis by administering infected dog-blood intravenously. Transient thrombocytopenia was the only hematological abnormality observed following inoculation of dogs with the attenuated strain. Challenge with the virulent strain resulted in severe disease in all 4 control dogs while only 3 of 8 vaccinated dogs presented mild transient fever. Furthermore, the mean blood rickettsial load was significantly higher in the control group (27-92-folds higher during days 14-19 post challenge with the wild the strain) as compared to the vaccinated dogs. The use of azithromycin was assessed as a therapeutic agent for the acute disease. Four days treatment resulted in further deterioration of the clinical condition of the dogs. Molecular comparison of 4 genes known to express immunoreactive proteins and virulence factors (p30, gp19, VirB4 and VirB9) between the attenuated strain and the challenge wild strain revealed no genetic differences between the strains. The results of this study indicate that the attenuated E. canis strain may serve as an effective and secure future vaccine for canine ehrlichiosis.

Original languageAmerican English
Pages (from-to)226-233
Number of pages8
Issue number1
StatePublished - 17 Dec 2012

Bibliographical note

Funding Information:
The authors are grateful to Dr. Daniel Yassur Landau, Dr. Dalit Talmi-Frank, Dr. Danny Morick, Sagy Polani, Yifat Guthmann, and Yael Mekuzas for their assistance in this study. This study was supported financially by grants from the Yissumit (# 0366108 ) and Yissum (Baby Seed # 0396859 ) programs of the Hebrew University .


  • Attenuation
  • Canine monocytic ehrlichiosis
  • Ehrlichia canis
  • Vaccine


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