Association between bat-predator species richness and Nipah virus spillover risk in Bangladesh.

Species biodiversity is considered to reduce infectious diseases spillover from wildlife to human. However, despite the potential role of predator biodiversity in this process through trophic cascade, few studies have addressed this issue. In this study, we investigated the association between predator biodiversity and spillover risk, using Nipah virus infection in Bangladesh as an example, where spillover from bats to human has been reported since 2021. We defined counties of Bangladesh as epidemiological units. From three Orders (Strigiformes, Accipitriformes, and Falconiformes) known as bat-preying predators, we extracted 39 species occurrences data and then built species distribution model using MaxEnt algorithm with climate and environmental predictors, also incorporating a bias grid to account for reporting bias. Species presence and richness were estimated under varying classification thresholds and species subsets reported to prey bats to allow sensitivity analyses, yielding 12 measures of species richness for each Order. We then used spatial model to identify the association between the species richness and the counties with spillover event, while adjusting for confounders. Results showed that greater biodiversity of owls (Strigiformes) is likely to reduce the risk of Nipah virus spillover. In contrast, the biodiversity of eagles (Accipitriformes) and falcons (Falconiformes) have a potential of positive association, but evidence was insufficient. This result can be explained by the differences in activity rhythms. Owls share a nocturnal activity rhythm with bats, providing more opportunities to prey on bats and reduce their activity, thereby lowering spillover risk. In contrast, eagles and falcons are diurnal, and thus less likely to suppress bat activity directly. Instead, they may suppress species that compete with bats for food, inadvertently facilitating bat activity and increasing spillover risk. These results suggest that biodiversity should be more explicitly considered in public health governance and spillover prevention strategies.