Doxycycline clearance of experimentally induced chronic Ehrlichia canis infection in dogs.

Author(s): Eddlestone SM, Diniz PP, Neer TM, Gaunt SD, Corstvet R, Cho D, Hosgood G, Hegarty B, Breitschwerdt EB

Affiliation(s): Department of Veterinary Clinical Sciences, Louisiana State University, School of Veterinary Medicine, Veterinary Clinical Sciences, Skip Bertman Drive, Baton Rouge, LA 7080, USA. seddlestone@vetmed.lsu.edu

Publication date & source: 2007-11, J Vet Intern Med., 21(6):1237-42.

Publication type: Randomized Controlled Trial; Research Support, Non-U.S. Gov't

BACKGROUND: Ineffective clearance of Ehrlichia canis after doxycycline administration has been reported despite the fact that the recommended treatment for canine ehrlichiosis is doxycycline. The effectiveness of doxycycline in clearing E canis infection from the blood and tissues of dogs requires additional evaluation. HYPOTHESIS: Doxycycline (5 mg/kg PO q12h), administered for 4 weeks, will eliminate E canis infection from the blood and tissues of experimentally infected dogs. ANIMALS: Fifteen Walker hound-mixed breed dogs were inoculated subcutaneously with E canis-infected canine histiocytic cells 4 months before doxycycline treatment. METHODS: Four dogs were treated with doxycycline (5 mg/kg PO q12h for 3 weeks), 5 dogs were treated with doxycycline at the same dosage for 4 weeks, and 5 control dogs were not treated. Dexamethasone (0.4 mg/kg i.v.) was given after treatment to precipitate recrudescence of any remaining E canis organisms. Platelet counts, anti-E canis immunofluorescent antibodies, and polymerase chain reaction (PCR) detection of E canis deoxyribonucleic acid (DNA) in blood and tissues were evaluated. RESULTS: E canis DNA was not detected in the blood and tissues of doxycycline-treated dogs after treatment. Platelet counts were within reference intervals, and E canis antibodies decreased. Spontaneous clearance of E canis infection occurred in 2 of 5 control dogs. Three control dogs had E canis DNA detected in blood and tissues, platelet counts remained low or within the reference interval, and E canis antibodies remained high. CONCLUSIONS AND CLINICAL IMPORTANCE: As administered in this study, doxycycline cleared E canis from the blood and tissues of experimentally infected dogs.