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Doxycycline clearance of experimentally induced chronic Ehrlichia canis infection in dogs
S M Eddlestone1, P P V P Diniz, T M Neer
1Department 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
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.
