PARENT SESSION

MOUNTING EVIDENCE FOR ACQUIRED IMMUNITY TO RABIES IN BATS. Thomas J. O'Shea¹, Vidya Shankar^2,3, Richard A. Bowen², Charles E. Rupprecht³ and Jeffrey H. Wimsatt⁴. ¹ U.S. Geological Survey, 2150 Centre Ave Bldg C, Fort Collins, CO; ² Department of Biomedical Sciences, Colorado State University, Fort Collins, CO; ³ Centers for Disease Control and Prevention, 1600 Clifton Road MS G-33, Atlanta, GA; ⁴ Center for Comparative Medicine, University of Virginia Health System, Charlottesville, VA.

ABSTRACT- Our joint field and laboratory studies suggest that bats may acquire immunity to rabies virus (RV). We conducted a serology survey of over 2,000 big brown bats (Eptesicus fuscus) at more than 20 colony sites in Fort Collins, Colorado in 2001, 2002, and 2003. Bats were marked with passive integrated transponder (PIT) tags for subsequent determination of their fate and for repeat blood sampling of known individuals. Serum was analyzed for the presence of RV neutralizing antibodies using the Rapid Fluorescent Focus Inhibition Test (RFFIT). Isolation of IgG from a sample of rabies seropositive bats and its subsequent effect in RFFIT demonstrated that the IgG fraction in the serum neutralizes RV. Seropositive big brown bats were found in every colony, and the seroprevalence (the proportion of bats with RV antibodies) in adult bats varied by roost, ranging from 3 to 35 %. Seropositive bats were recaptured or demonstrated to be alive by PIT tag readers 1-2 years following the initial detection of RV antibodies. RV antibodies also persisted 1-2 years after the first sampling, longer than any expected incubation period for RV. We also report: results of reverse transcriptase polymerase chain reaction (RT-PCR) assays for the detection of RV genome in tissues of seropositive bats known to be alive one year after initial blood sampling; changes in overall seroprevalence by age groupings of bats; and seroprevalence data for additional species of bats, including silver-haired bats (Lasionycteris noctivagans), hoary bats (Lasiurus cinereus), little brown bats (Myotis lucifugus), long-legged myotis (Myotis volans) and other species sampled in Colorado and in New Mexico. These data support the hypothesis that bats are commonly exposed to the RV and can acquire immunity, perhaps through exposure to low doses of RV that do not result in productive virus infection. Results are consistent with preliminary findings by our group based on experimental exposures of big brown bats to RV in the laboratory. The immunity conferred to segments of bat populations together with their ability to endure some level of RV exposure may explain why it is uncommon to observe widespread decimation of entire colonies of bats by rabies epizootics.

KEY WORDS: rabies, acquired immunity, bats, Eptesicus fuscus