The response of the meadow vole (Microtus pennsylvanicus) to infection by experimental inoculation with Borrelia burgdorferi was evaluated. Forty-two adult voles were inoculated subcutaneously with 0.5 × 106 spirochetes. Sera taken during the 196 day trial were tested by indirect fluorescent antibody (IFA) assay for antibodies to B. burgdorferi. Tissues from animals which died during the trial, and from animals killed at 28, 112 and 196 days post-inoculation (DPI), respectively, were cultured in BSK-II medium for ≤6 weeks. They also were examined histologically for lesions and the presence of spirochetes. All inoculated animals developed antibodies by 14 DPI and maintained titers ≥1:10 for the duration of the trial. Spirochetes were isolated from ears, bladder, and spleen. Spirochetes also were identified by Bosma-Steiner silver stain or tissue IFA assay in sections of ears, bladder, kidney and heart. Infection as confirmed by re-isolation persisted for ≤111 days. No lesions were identified in association with the presence of spirochetes. No increase in mortality was observed in inoculated animals compared with controls.
Sensitivity of the IFA test at a cut-off titer of 1:10 was 100% from ≥14 DPI, but at 1:20 reached a maxiumum of 97%. Specificity at 1:10 was 84% and at 1:20 was 97%. Use of antiserum to Microtus immunoglobulin (Ig) in a double-layered test provided no significant advantages over use of a commercial fluorescein-conjugated anti-mouse Ig in a single-layered IFA test.