An animal model for Lyme arthritis.

A model of Lyme arthritis has been developed in laboratory rats. Intraperitoneal inoculation of a low-passage tick isolate of B. burgdorferi into neonatal and weanling LEW/N rats resulted in multisystemic infection and arthritis. Spirochetes were isolated from blood, liver, kidney, spleen, brain, and joints of inoculated rats. Arthritis, associated with the presence of spirochetes, developed in multiple joints by day 14 and persisted through day 90 after inoculation. Arthritic lesions resembled those found in human Lyme disease lesions. Lesions were not found in other organs, although spirochetes were present. Neonatal F344 and SD rats were also susceptible to infection and induction of arthritis. Three different isolates of B. burgdorferi were shown to be pathogenic. Pathogenicity of one isolate was retained after at least 11 in vitro passages. Formalin-killed spirochetes were not pathogenic. Other features of the Lyme disease complex have yet to be seen in the rat, but long-term studies are required to completely define the rat model. This highly reproducible model should allow in-depth studies on the pathogenetic mechanisms of this important human disease.