Low-tech approach stifles high-risk Nipah virus

Shielding palm-tree sap from fruit bats may limit spread of deadly disease

WASHINGTON — Simple bamboo skirts attached to date palms can protect the trees’ tasty sap from contamination by fruit bats. In so doing, the low-tech devices may prevent the spread of lethal Nipah virus, researchers in Bangladesh report at a meeting of the American Society of Tropical Medicine and Hygiene.

PREVENTIVE MEASURE In Bangladesh, bamboo shields keep delicious palm sap from being tainted by fruit bats that can spread the rare but lethal Nipah virus. M. Salah Uddin Khan

Nipah virus is a relatively new pathogen that was first identified in 1999. The virus can spread from person to person but is more likely to pass from an animal to a person. Fruit bats — known as flying foxes and common in Southeast Asia — can carry the virus without being sickened by it. 

“This is basically a bat virus that occasionally spills over into other animals, including Homo sapiens,” says study coauthor Stephen Luby, a physician at the Centers for Disease Control and Prevention in Atlanta and the International Center for Diarrheal Disease Research, Bangladesh in Dhaka.

In Bangladesh, people harvest the sweet sap of date palms by shaving part of the trunk, slicing a groove in it and attaching a collection pot. But in recent years, researchers have determined that fruit bats have been sullying the sap with saliva or urine that drips down the trunk into the pots.

This is more than a mere annoyance to people collecting the sap, which is a delicacy in Bangladesh. Nipah virus causes encephalitis, or brain inflammation, and infections prove fatal in about three-fourths of cases, says veterinarian M. Salah Uddin Khan, also of the ICDDR-Bangladesh, who will present the findings on November 21. 

Khan’s colleague Nazmun Nahar learned from villagers that handwoven bamboo skirts had been used from time to time to guard the sap-collection pots from fruit bats. The skirts cover the shaved part of the trunk and the top of the pot. At Nahar’s request, villagers made such a skirt, and the scientists used it as a prototype, producing nine more to test whether the skirts could prevent palm sap contamination.

Using motion-activated infrared cameras, the scientists tracked fruit bats’ nocturnal visits to 20 palm trees that had collection pots attached. The researchers attached skirts to 10 trees and left the other 10 unprotected, then examined the sap for evidence of bat contamination in the morning. The next night they reversed which trees got the bamboo skirts.

Sap collected from unprotected palms was tainted 85 percent of the time. Sap from a few of the skirt-equipped palms also was sullied, due to faulty skirt construction or placement. But 13 of 13 palms with intact, properly placed skirts yielded clean sap.

Nipah virus is rare: There have been only 132 confirmed cases since the virus was identified in 1999, Khan says. The virus is named for the Nipah Valley in Malaysia, where it was first discovered. In Malaysia, transmission occurs largely from animals to people, with pig farmers at high risk. But in Bangladesh, most cases have been linked to palm sap contamination by bats.

Date palm sap collection is a rural phenomenon in Bangladesh, Luby says, so the researchers are now exploring ways to promote the use of skirts during sap harvesting.