Project Summary Nipah virus is a zoonotic paramyxovirus, carried by old world fruit bats across Africa and Asia, which causes severe, fatal encephalitis in humans and can be transmitted from person to person. In Bangladesh, where outbreaks in people occur annually, the primary route of transmission is the consumption of raw date palm sap. Date palm sap is harvested and consumed most intensively in western Bangladesh, an area referred to as the “Nipah belt,” however, date palm sap consumption, NiV, and its bat reservoir, Pteropus medius, are present throughout Bangladesh. It is unclear why outbreaks have not been detected in eastern Bangladesh. Cryptic spillover of NiV creates a significant risk that more pathogenic and transmissible strains will emerge and lead to large epidemics. This multidisciplinary project will determine whether NiV outbreaks have occurred in eastern Bangladesh and how differences human behavior, infection patterns in bats, and genetic variation in circulating strains of NiV influence outbreaks outside of the Nipah belt. This project combines human exposure studies with multi-site longitudinal infection studies in bats and in vivo experimental infections in bats and hamsters comparing clinical outcomes among diverse strains to achieve the following specific aims: 1) To compare NiV exposure and its behavioral determinants among human populations inside and outside the Nipah belt in Bangladesh. We will test the hypothesis that NiV spillover has occurred in Bangladesh in communities outside the Nipah belt. We’ll use behavioral questionnaires and a multiplex Luminex serological assay to screen high risk populations for IgG antibodies against NiV and determine if Nipah exposure has occurred and how behavioral risk varies by locality. 2) To compare Nipah virus temporal dynamics in Pteropus bat colonies inside and outside of the Nipah belt. We will conduct longitudinal bat NiV field studies in six locations (3 western, 3 eastern), characterize local bat demography, measure changes in seroprevalence over time; determine viral shedding patterns and genetic variation among strains. Through experimental bat infections in a BSL 4 lab, we will determine whether bats with antibodies against NiV (previous exposure) may be re-infected and shed virus. This will answer a critical question about transmission dynamics and allow us to test the hypothesis that viral shedding occurs with different frequency in eastern bats compared to western bats, which may influence zoonotic transmission. 3) To compare pathogenicity and transmissibility of diverse Nipah virus isolates from bats inside and outside the Nipah belt, using animal models. Malaysia type NiV and Bangladesh type have different clinical profiles in people. NiV genetic variation may account for lower human infection rates in eastern Bangladesh. To test this hypothesis, we will compare transmissibility and pathogenicity of diverse NiV strains isolated from Pteropus medius in...