Lyme borreliosis in laboratory animals: effect of host species and in vitro passage of Borrelia burgdorferi.

The susceptibility of several common laboratory animal species to a known pathogenic isolate of Borrelia burgdorferi (N40) was evaluated following intraperitoneal (ip) inoculation of 10(6-8) spirochetes into 3-day-old Lewis rats, CD-1 mice, Syrian hamsters, and 3-week-old American Dutch rabbits. At 30 days, tissues were cultured for spirochetes and examined histologically. All species developed multisystemic infection as well as arthritis and carditis, but disease was most severe in rats and mice. In order to evaluate the effect of in vitro passage on the pathogenicity of B. burgdorferi, 3-day-old Lewis rats were inoculated ip with borreliae passaged in culture 2, 5, 11, 17, 21, 26, and 31 times, and evaluated at 30 days by culture, histology, and ELISA antibody titers. Based upon these parameters, B. burgdorferi (N40) lost its virulence at 17-21 passages. This study demonstrated that B. burgdorferi was infectious for infant rats, mice, hamsters, and 3-week-old rabbits, although pathogenicity was modulated by host species and the in vitro passage history of the spirochete. Of the 4 laboratory animal species evaluated in this study, rats and mice appear to have the most potential for further use as animal models of Lyme disease.