Public health professionals strive to understand how viruses are distributed in the environment, the factors that facilitate viral transmission, and the diversity of viral agents capable of infecting humans to characterize disease burdens and design effective disease intervention strategies. The public health discipline of conservation medicine supports this endeavor by encouraging researchers to identify previously unknown etiologic agents in wildlife and analyze the ecologic of basis of disease. Within this framework, this research reports the first examination of the prevalence in Southeast Asia of the orthoreovirus Nelson Bay virus in humans and in the Pteropus bat reservoir of the virus. Contact with Pteropus species bats places humans at risk for Nipah virus transmission, an important emerging infectious disease. This research furthermore explores the environmental determinants of Nelson Bay and Nipah viral prevalence in Pteropus bats and reports the characterization of two novel orthoreoviruses isolated from bat tissues collected in Bangladesh.