PERSISTENCE OF BORRELIA-BURGDORFERI IN EXPERIMENTALLY INFECTED-DOGS AFTER ANTIBIOTIC-TREATMENT

In specific-pathogen-free dogs experimentally infected with Borrelia b urgdorferi by tick exposure, treatment with high doses of amoxicillin or doxycycline for 30 days diminished but failed to eliminate persiste nt infection. Although joint disease was prevented or cured in five of five amoxicillin- and five of six doxycycline-treated dogs, skin punc h biopsies and multiple tissues from necropsy samples remained PCR pos itive and B. burgdorferi was isolated from one amoxicillin- and two do xycycline-treated dogs following antibiotic treatment. In contrast, B. burgdorferi was isolated from six of six untreated infected control d ogs and joint lesions were found in four of these six dogs. Serum anti body levels to B. burgdorferi in all dogs declined after antibiotic tr eatment. Negative antibody levels were reached in four of six doxycycl ine- and four of six amoxicillin-treated dogs. However, in dogs that w ere kept in isolation for 6 months after antibiotic treatment was disc ontinued, antibody levels began to rise again, presumably in response to proliferation of the surviving pool of spirochetes. Antibody levels in untreated infected control dogs remained high.