Background . The effect of anti—tumor necrosis factor (TNF)—α treatment in Borrelia burgdorferi—infected and ceftriaxone-treated C3H/He mice was evaluated.

Methods . Mice were infected with B. garinii Å218 or B. burgdorferi sensu stricto N40. At 2 weeks of infection, one group was treated simultaneously with ceftriaxone and anti—TNF-α, whereas another received ceftriaxone at 2 weeks and anti—TNF-α 4 weeks later. One group received ceftriaxone treatment only. Infected and noninfected control groups were sham treated.

Results . At 14 weeks of infection, B. burgdorferi could not be detected by cultivation or by polymerase chain reaction in tissue samples of any mouse treated with ceftriaxone only. However, spirochetes grew from the tissue samples of one-third of the mice treated with anti—TNF-α simultaneously or 4 weeks after ceftriaxone. These activated spirochetes showed ceftriaxone sensitivity rates, plasmid profiles, and virulence rates similar to those of bacteria used to infect the mice. All infected control mice and mice given anti—TNF-α only were culture positive.

Conclusions . This report shows that, after ceftriaxone treatment for 5 days, a portion of B. burgdorferi—infected mice still have live spirochetes in their body, which are activated by anti—TNF-α treatment.