PCR-based quantification of Borrelia burgdorferi organisms in canine tissues over a 500-day postinfection period

Borrelia burgdorferi infection in beagle dogs was studied quantitatively wi th skin punch biopsy samples and blood samples collected at 4- and 2-week i ntervals, respectively, over a 500-day period, Thereafter, 25 tissue sample s of each dog were collected for further analysis. Starting at day 120 afte r tick challenge, 12 dogs were treated with antibiotics (azithromycin, ceft riaxone, or doxcycline) for 30 consecutive days, Four dogs received no anti biotic therapy. Quantification of B. burgdorferi DNA was done with an ABI P rism 7700 Sequence Detection System with oligonucleotide primers and a fluo rescence-labeled probe designed to specifically amplify a fragment of the o spA gene of B. burgdorferi strain N40, All 16 dogs became infected with B, burgdorferi after tick challenge. In skin biopsy samples, spirochete number s peaked at day 60 postinfection (<1.5 x 10(6) organisms per 100 mu g of ex tracted DNA), at the same time when clinical signs of arthritis developed i n 11 of 16 dogs, and decreased to almost undetectable levels during the fol lowing 6 months. The number of B. burgdorferi organisms detected in skin bi opsy samples was inversely correlated with the antibody levels measured by enzyme-linked immunosorbent assay. Antibiotic treatment reduced the amount of detectable spirochete DNA in skin tissue by a factor of 1,000 or more. A t the end of the experiment, B. burgdorferi DNA was detectable at low level s (10(2) to 10(4) organisms per 100 mu g of extracted DNA) in multiple tiss ue samples regardless of treatment. However, more tissue samples of untreat ed dogs than of antibiotic-treated dogs were positive, and tissue samples o f untreated dogs also were positive by culture. Only 1.6% of 576 blood samp les of all dogs were positive for B. burgdorferi by PCR.