Ecology of Virus Transmission in Commensal Bats

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Rabies commonly circulates in populations of commensal bats (bats that live in close proximity to humans). In Colorado, bats have been virtually the only wildlife associated with human exposures to rabies. From 2001–2006, FORT biologists investigated the ecological dynamics of rabies transmission in big brown bat (Eptesicus fuscus) populations that roost and live within cities, using Fort Collins, Colorado, as the case study. Project collaborators included Colorado State University, the Centers for Disease Control and Prevention, the National Science Foundation, the National Institutes of Health, and the Colorado Department of Public Health and Environment. The 5-year study was completed in 2006, emphasizing host demography and viral exposure. Investigators are completing data analysis, modeling, and publication work. Final results include a new model for rabies transmission in bats and are expected to be of considerable interest to public health agencies and bat conservationists. Modeling suggests that rabies maintenance is determined by factors affecting (1) a viable bat population and (2) sufficient pathogen transmission within the viable bat population. Seasonal variability in bat mortality rates, especially low mortality during hibernation, allows long-term bat population viability. Within viable bat populations, sufficiently long incubation periods allow enough infected individuals to enter hibernation and avoid an epizootic fadeout of rabies virus. We hypothesize that the slowing effects of hibernation on metabolic and viral activity maintains infected individuals and their pathogens until susceptibles from the annual birth pulse become infected and continue the cycle. For more information on the study, visit the Colorado State University project site at