The pine vole, Microtus pinetorum, was evaluated as a laboratory animal model for infection with Rickettsia rickettsii. Voles demonstrated signs of acute disease, and 45% of infected animals died following intraperitoneal infection with 3 x 10(6) plaque forming units of R. rickettsii. Spleen, liver, kidney, lung, brain, testes and blood were analyzed for rickettsial burden by a quantitative PCR assay. The distribution of rickettsiae in tissues during the course of infection was determined by immunohistochemical staining and pathological changes in tissues were correlated with the clinical severity of infection. Quantitative RT-PCR assays were designed to measure the mRNA levels of the antioxidant enzyme genes for catalase, glutathione peroxidase, glutathione reductase, heme oxygenase, Cu-Zn superoxide dismutase (SOD) and Mn-SOD, and 2 housekeeping genes, actin and glyceraldehyde phosphate dehydrogenase. Tissues from acutely ill animals on days 2 to 6 of infection, convalescent animals, and uninfected control animals were studied. The number of transcripts of each enzyme gene was determined and compared to the degree of rickettsial infection present. These studies demonstrate that the pine vole is a valuable experimental model for studying infection with R. rickettsii. Our results provide the first experimental evidence that R. rickettsii causes alteration(s) of the anti-oxidant system in vivo.