Bats are among the most diverse mammals on Earth and comprise more than 1200 species. Several bat species have been identified as reservoirs for significant zoonotic viruses such as SARS coronavirus, Nipah virus, Marburg and Ebola viruses, and rabies virus. Bats live in almost every type of ecosystem and are highly adapted to humanized environments. As such, bats have learned to exploit anthropogenic resources (e.g. mines, buildings, fruit orchards, etc...). This close association between bats and people creates opportunities for pathogen spillover. Routes of viral transmission are frequently indirect (not from bites or scratches) and involve contamination of food, air, or water resources with excreta and infectious viral particles. Nipah virus (NiV) is a zoonotic virus carried by pteropid fruit bats that emerged on a large-scale pig farm in Malaysia in 1997 and led to the death of 105 people (265 infected) and the closure of thousands of farms and destruction of millions of pigs. Since 2001, Nipah virus has been identified as the cause of seasonal outbreaks of encephalitis in Bangladesh. Large-scale ecological studies of Nipah virus in Malaysia and Bangladesh have helped elucidate NiV dynamics in bats and causes of spillover and amplification.
Results/Conclusions
In Malaysia, fruit orchards planted next to pig enclosures on large-scale farms attracted fruit bats. Pigs accessing and being fed dropped fruit contaminated with bat excreta exposed them to Nipah virus. In Bangladesh, consumption of date palm sap is a major route of NiV infection. Date palm sap is cultivated in villages throughout Bangladesh during the winter months. It is a food resource not naturally available to bats, as it requires the carving of bark from the tree trunks to expose the sap. Sap is harvested in the winter when fruits normally eaten by bats are less available. Bats drink sap as it flows into collection pots, contaminating it with excreta and occasionally Nipah virus. In both Malaysia and Bangladesh, human activities inadvertently provided food resources for bats which facilitated Nipah virus spillover and emergence. Interventions have included policies requiring a buffer zone between orchards and livestock enclosures (Malaysia), and the use of bamboo skirts to cover date palm sap collection pots to exclude bats (Bangladesh). Recognizing anthropogenic human-wildlife interfaces early and developing measures that limit wildlife access to human food sources are critical steps for preventing spillover and the emergence of zoonotic pathogens.