J Infect Dis. 2002 Nov 15;186,10:1430-7. Epub 2002 Oct 23. Detection of attenuated, noninfectious spirochetes in Borrelia burgdorferi-infected mice after antibiotic treatment. Bockenstedt LK, Mao J, Hodzic E, Barthold SW, Fish D. Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8031, USA. linda.bockenstedt@yale.edu Xenodiagnosis by ticks was used to determine whether spirochetes persist in mice after 1 month of antibiotic therapy, Doxycyline and Ceftriaxone, for vectorborne Borrelia burgdorferi infection. Immunofluorescence and polymerase chain reaction, PCR, were used to show that spirochetes could be found in Ixodes scapularis ticks feeding on 4 of 10 antibiotic-treated mice up to 3 months after therapy. These spirochetes could not be transmitted to naive mice, and some lacked genes on plasmids correlating with infectivity. By 6 months, antibiotic-treated mice no longer tested positive by xenodiagnosis, and cortisone immunosuppression did not alter this result. Nine months after treatment, low levels of spirochete DNA could be detected by real-time PCR in a subset of antibiotic-treated mice. In contrast to sham-treated mice, antibiotic-treated mice did not have culture or histopathologic evidence of persistent infection. These results provide evidence that noninfectious spirochetes can persist for a limited duration after antibiotics but are not associated with disease in mice