Use of infrared camera to understand bats' access to date palm sap: implications for preventing Nipah virus transmission

Abstract

Pteropus bats are commonly infected with Nipah virus, but show no signs of illness. Human Nipah outbreaks in Bangladesh coincide with the date palm sap harvesting season. In epidemiologic studies, drinking raw date palm sap is a risk factor for human Nipah infection. We conducted a study to evaluate bats' access to date palm sap. We mounted infrared cameras that silently captured images upon detection of motion on date palm trees from 5:00 pm to 6:00 am. Additionally, we placed two locally used preventative techniques, bamboo skirts and lime (CaCO₃) smeared on date palm trees to assess their effectiveness in preventing bats access to sap. Out of 20 camera-nights of observations, 14 identified 132 visits of bats around the tree, 91 to the shaved surface of the tree where the sap flow originates, 4 at the stream of sap moving toward the collection pot, and no bats at the tap or on the collection pots; the remaining 6 camera-nights recorded no visits. Of the preventative techniques, the bamboo skirt placed for four camera-nights prevented bats access to sap. This study confirmed that bats commonly visited date palm trees and physically contacted the sap collected for human consumption. This is further evidence that date palm sap is an important link between Nipah virus in bats and Nipah virus in humans. Efforts that prevent bat access to the shaved surface and the sap stream of the tree could reduce Nipah spillovers to the human population.