EXPLORATORY ANALYSIS OF COLLECTED BAT AND TREE DATA FROM DATE PALM SAP HARVESTING IN BANGLADESH FROM DECEMBER 2023 TO MARCH 2024

Abstract

In Bangladesh, the primary route of human exposure to zoonotic Nipah virus is through the consumption of date palm sap that has been contaminated with saliva, urine, or feces from Pteropus bats. Since the first outbreak in 2001, there have been almost annual human infections, with more outbreaks occurring in colder winters. Identifying a relationship between sap sweetness and quantity may provide insight into the factors driving the rise in Nipah cases during colder months. Additionally, understanding the timing of Pteropus visitations is critical, as increased visitation rates create more opportunities for date palm sap contamination and, consequently, a higher risk of spillover events. In this study, we aimed to better understand what factors, including weather and the ecology of bats and date palm trees, affect the frequency of sap contamination by bats. Between December 2023 to May 2024, infrared cameras were set up on 20 date palm trees for eight nights of observation in Bangladesh. For both Pteropus and non-Pteropus bats, there were more visitations in colder months, December (np = 155, nnp = 954) and January (np = 521, nnp = 1289). Overall, non-Pteropus bats visited more frequently than Pteropus bats. Measurements of date palm sap yield and sweetness showed that more, but less sweet sap was produced at lower temperatures. A slight negative trend (p = 0.664) was observed between sap quantity and sweetness, while a slight positive trend was found between sap quantity and total bat visitations for both Pteropus (p < 0.001) and non-Pteropus (p < 0.001) species. Among non-Pteropus bats, there was a slight positive trend between visitations and sap sweetness, but no such trend was observed for Pteropus bats. Based on our study findings, colder weather produced more (p-value = 0.003) but less sweet (p = 0.35) sap. Additionally, the increase in bat visitations to date palm trees seem to be more driven by colder temperature rather than sap quantity or sweetness