Persistence of Borrelia burgdorferi following antibiotic treatment in mice.

The effectiveness of antibiotic treatment was examined in a mouse model of Lyme borreliosis. Mice were treated with ceftriaxone or saline solution for 1 month, commencing during the early (3 weeks) or chronic (4 months) stages of infection with Borrelia burgdorferi. Tissues from mice were tested for infection by culture, PCR, xenodiagnosis, and transplantation of allografts at 1 and 3 months after completion of treatment. In addition, tissues were examined for the presence of spirochetes by immunohistochemistry. In contrast to saline solution-treated mice, mice treated with antibiotic were consistently culture negative, but tissues from some of the mice remained PCR positive, and spirochetes could be visualized in collagen-rich tissues. Furthermore, when some of the antibiotic-treated mice were fed on by Ixodes scapularis ticks (xenodiagnosis), spirochetes were acquired by the ticks, as determined based upon PCR results, and ticks from those cohorts transmitted spirochetes to naïve SCID mice, which became PCR positive but culture negative. Results indicated that following antibiotic treatment, mice remained infected with nondividing but infectious spirochetes, particularly when antibiotic treatment was commenced during the chronic stage of infection.

Coinfection with Anaplasma phagocytophilum alters Borrelia burgdorferi population distribution in C3H/HeN mice.

Borrelia burgdorferi, the agent of Lyme disease, and Anaplasma phagocytophilum, the agent of human anaplasmosis, are both transmitted by Ixodes sp. ticks and may occasionally coinfect a host. The population distributions of tick-transmitted B. burgdorferi infection were assessed using quantitative PCR targeting the flaB gene of B. burgdorferi in the ear, heart base, quadriceps muscle, skin, and tibiotarsal joint tissue of C3H mice previously infected with A. phagocytophilum. Population distributions of Anaplasma infection were assessed by targeting the p44 gene. A. phagocytophilum in blood and serologic response to both agents were evaluated. Spirochete numbers were increased in the ears, heart base, and skin of coinfected mice, but Anaplasma numbers remained constant. Antibody response to A. phagocytophilum, but not B. burgdorferi, was decreased in coinfected mice. These results suggest that coinfection with A. phagocytophilum and B. burgdorferi modulates pathogen burden and host antibody responses. This may be explained by the ability of A. phagocytophilum to functionally impair neutrophils, important cells in the early defense against B. burgdorferi infection.

Borrelia burgdorferi population kinetics and selected gene expression at the host-vector interface.

By using real-time quantitative PCR, the population dynamics and gene transcription of Borrelia burgdorferi were examined in ticks and skin of mice during acquisition of the infection from mice by ticks and during transmission of the infection from ticks to mice. Population dynamics were determined by using a flaB DNA target. A quantitative analysis of flaB, ospA, ospC, dbpA, and arp transcription was also performed. The results revealed that both uninfected larval and nymphal Ixodes scapularis ticks acquired B. burgdorferi as early as 1 day after attachment and that the sizes of spirochete populations within ticks increased during feeding. In addition, all gene targets revealed that there was RNA transcription during feeding. Similar events occurred within infected nymphal ticks feeding on uninfected hosts. Transmission from infected nymphal ticks to mice could be detected within 1 day after attachment. Analysis of skin during the first 3 days after attachment of infected ticks revealed rising numbers of spirochetes but minimal gene transcription. In contrast, the skin of mice with established infections revealed static populations of spirochetes and active but stable transcription of flaB, ospC, dbpA, and arp. There were consistent reductions in the number of spirochetes in the skin at the tick attachment sites compared to the number of spirochetes in the skin at nontick sites, but there were no differences in gene expression between tick and nontick skin sites. Evidence of ospA transcription in skin could be found 1 day after tick attachment but not thereafter.