A new NIAID study shows that Nipah virus infection can occur after consuming sap contaminated with the virus. The result provides additional evidence that infected fruit bats likely are contaminating sap harvested from date palm trees, thus spreading the virus to people in parts of Southeast Asia.
Nipah virus first was identified in 1998 when an outbreak in Malaysia and Singapore sickened 276 people. To date, there have been more than 500 cases with nearly 300 deaths throughout parts of Southeast Asia.
The virus targets the lungs and causes brain swelling. While infection is rare, the disease is fatal about 75 percent of the time. Those who survive often experience chronic brain damage. Bangladesh is an example of a region where Nipah virus is a great concern. The nation has experienced outbreaks almost every year since 2001. In 2013, Bangladesh reported 24 Nipah cases that resulted in 21 deaths; through Feb. 11, 2014, 18 cases had been reported with nine deaths. Malaysia, Singapore, and India also have reported cases.
There is no treatment for Nipah, though scientists are continuing studies of an experimental vaccine and treatment.
Fruit bats are thought to be the natural reservoir, or carrier, of Nipah virus. Though no research groups have proven the connection, scientists suspect that the main transmission route from bats to humans in Bangladesh involves bats contaminating the sweet sap that people consume from date palm trees—think of how maple syrup is harvested by tapping the tree and collecting the sap that flows. Bats have been observed roosting in date palm trees and sampling the harvested sap. Scientists also know that Nipah virus is present in the saliva and urine of these bats, which is likely how the virus ends up in the sap.
Scientists at NIAID Rocky Mountain Laboratories (RML) showed that Nipah virus survives in artificial date palm sap for at least seven days, making the sap a potential source of foodborne Nipah virus transmission.
The researchers then allowed eight hamsters to drink the virus-contaminated artificial palm sap. Five of the animals developed disease consistent with what occurs in people, establishing that foodborne transmission is possible. The group also used fluorescently labeled virus particles to track spread of the virus in the lungs while hamsters consumed the sap.
Further, the scientists showed that virus could transmit directly from one animal to another by close contact. Twenty-four sap-infected hamsters were housed in pairs with healthy hamsters, two of which became infected with Nipah virus.
Residents in Bangladesh have successfully, but inconsistently, used tree skirts to keep bats away from the vats that collect the flowing sap. Having scientific evidence that the virus can transmit through contaminated sap and cause disease will enhance efforts to limit the access bats have to the sap.
Credit: J. Epstein, EcoHealth Alliance, Copyright 2014
RML investigators and their colleagues are continuing to test and develop treatments for Nipah virus and the closely related Hendra virus, which also is spread by fruit bats. The vaccine concept that has shown success against Nipah virus also has been successful against Hendra. Hendra virus emerged in 1994 in Australia and primarily affects horses, which can spread the disease to humans. No person-to-person transmission of Hendra virus has been reported. A licensed vaccine for horses now available in Australia is expected to reduce the infection risk for humans there.
E de Wit et al. Foodborne transmission of Nipah virus in Syrian hamsters. PLoS Pathogens DOI: 10.1371/journal.ppat.1004001 (2014).
Last Updated March 14, 2014
Last Reviewed March 14, 2014