Convergence of Humans, Bats, Trees, and Culture in Nipah Virus Transmission, Bangladesh

Abstract

Preventing emergence of new zoonotic viruses depends on understanding determinants for human risk. Nipah virus (NiV) is a lethal zoonotic pathogen that has spilled over from bats into human populations, with limited person-to-person transmission. We examined ecologic and human behavioral drivers of geographic variation for risk of NiV infection in Bangladesh. We visited 60 villages during 2011-2013 where cases of infection with NiV were identified and 147 control villages. We compared case villages with control villages for most likely drivers for risk of infection, including number of bats, persons, and date palm sap trees, and human date palm sap consumption behavior. Case villages were similar to control villages in many ways, including number of bats, persons, and date palm sap trees, but had a higher proportion of households in which someone drank sap. Reducing human consumption of sap could reduce virus transmission and risk for emergence of a more highly transmissible NiV strain.

Keywords: Bangladesh; NiV; Nipah virus; bats; case–control study; convergence; culture; date palm sap; epidemiology; human behavior; humans; infections; trees; vector-borne infections; virus transmission; viruses; zoonoses.

Figure 1

A) Locations of identified bat-to-human transmission of Nipah virus and spatial intensity of transmission events, Bangladesh, 2001–2012. B) Relative sizes of the Pteropus medius bat populations in case and control villages (including within 5 km of each village). C) Proportion of households in case and control villages with persons who regularly consume fresh date palm sap.

Figure 2

Comparisons of villages with Nipah virus infections with nearby and distant control villages, Bangladesh, 2011–2013. A) Human population size, B) Pteropus medius bat population size, C) no. date palm trees, D) proportion of households with members who consume fresh date palm sap, E) average no. of persons per household who consume fresh date palm sap, and F) proportion of households that reported their residents eat bitten fruits dropped on the ground. Gray shading in violin plots indicates distribution of values for each variable. Box plots indicate 25th and 75th percentiles (bottom and top lines), medians (horizontal lines within boxes), and 95 CIs (whiskers). Red dots indicate maximum (outlier) values.