The results of a six-year study conducted by the nonprofit EcoHealth Alliance were released this week, and the data revealed that Nipah virus is not as confined to what is traditionally known as the Nipah belt along the Bangladesh-India border as previously thought.
Bats throughout Bangladesh were found with similar patterns of Nipah virus infection over the course of the study. In the past, Nipah cases have broken out in Malaysia, Singapore, and the Philippines. Writing in the journal Proceedings of the National Academy of Sciences of the United States of America, EcoHealth researchers studied eight bat colonies from 2006 to 2012. They found Nipah antibodies in each, and in one colony, outbreaks occurred about every two years — approximately the time it takes for bats to lose herd immunity.
“Nipah circulates regularly in large fruit-eating bats throughout many parts of Asia, but human outbreaks can only occur where there is a route of transmission from bats to humans,” Dr. Jonathan Epstein, lead author and EcoHealth Alliance vice president for science and outreach, said. “The problem is, we don’t have a good handle on where else in the world spillover may be happening, which means we’re likely missing outbreaks. Risk is not so much limited by geography as it is by human behavior. This is a virus that spreads from person to person and is lethal in three-quarters of those it infects, which is why we have to pay close attention to it and do what we can to prevent outbreaks.”
Nipah is a distant relative of measles but has no vaccine and no effective medical countermeasures. It can cause brain swelling and comas. Outbreaks are often linked to consumption of raw date palm sap and through contact with intermediate hosts such as domesticated animals or bats.
“Finding that bats carrying Nipah virus can be infected anywhere and at any time of year means we have to pay closer attention in areas where Nipah outbreaks may not have been previously reported, to make sure we’re not missing small outbreaks that could lead to bigger ones,” Epstein said.
Another major concern raised by the study was that different Nipah virus strains tended to crop up in different areas of the country. Human outbreak capable Nipah strains often reflected those carried by local bats. Researchers are still studying whether genetic differences in the virus impact disease severity of transmissibility in humans.