Post-therapy antibody titers in dogs with ehrlichiosis: follow-up study on 68 patients treated primarily with tetracycline and/or doxycycline.

The clinical and serological responses to therapy were evaluated for at least 1 year in 68 dogs with antibody titers positive for Ehrlichia canis. Treatments were of variable periods with primarily tetracycline hydorchloride and/or doxycycline. Sixteen dogs had initial titers of 1:20 and, at the end of the year, were asymptomatic, no longer receiving medication, and had negative serology. The average length of treatment with tetracycline HCl and/or doxycycline was 85 days (range, 14 to 360 days). Of 39 dogs with initial titers of 1:2,560 or greater, 1 died, 25 were asymptomatic, and 13 were lost to follow-up at the end of the study. The average length of treatment was 210 days (range, 21 to 630 days). Twenty-seven dogs were seropositive at > or = 1:2,560 when the sera was last tested. Thirteen dogs had initial titers of 1:80 to 1:1,280. Of these 13 dogs, 2 died, 2 were lost to follow-up, and 9 were asymptomatic and had titers ranging from negative to > or = 1:2,560 at the end of the study. The persistence of antibodies, prolonged subclinical phase, and delayed relapses despite long-term medication, suggest inadequate chemotherapeutic agents or may be natural features of latency of ehrlichiosis in dogs.