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Bat-borne infection spreads through contaminated date palm wine
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Fermented date palm sap contaminated with bat excrement appeared to be the source of an outbreak of Nipah virus in Bangladesh, according to a recent investigation.
First detected in a 1998 outbreak affecting 283 Malaysians, Nipah virus (NiV) infections occur almost annually in Bangladesh and India, the researchers wrote. These are often attributed to contact with the disease’s natural reservoir, Pteropus spp. bats, as human-to-human transmission of NiV is less common. They wrote that previous outbreak investigations have identified the consumption of raw date palm sap as the primary route of NiV transmission between bats and humans.
“In Bangladesh, date palm sap is typically collected in clay pots that are attached to the tree,” the researchers wrote. “A top section of the date palm tree bark is shaved, allowing the sap to ooze overnight into the collection pot. A previous NiV study reported that Pteropus spp. bats frequently feed on the shaved bark and often contaminate the sap with saliva, urine and excreta.”
From December 2010 to March 2014, surveillance detected 18 clusters of NiV infection. Although 15 of these were attributed to fresh date palm sap exposure, the index cases in the remaining three clusters reported no known contact with date palm saps, bats or other sick animals.
To determine the initial source of transmission, the researchers conducted an epidemiological investigation within the Rajshahi and Rangpur districts of Bangladesh. They collected clinical histories and whole blood samples of suspected case-patients, and visited surviving patients within 1 month of diagnosis. A questionnaire was used to interview surviving case-patients and their friends and families about potential exposures or symptoms of illness. Because preliminary data suggested patients may have consumed tari — an alcoholic drink made from fermented date palm sap — researchers also interviewed sap harvesters and analyzed whole blood samples from community members who drank tari but did not become ill.
Fourteen case-patients with confirmed or suspected illness were identified within the three investigated clusters. Eight of these were considered primary cases who experienced fever, altered mental status, loss of consciousness and death during a median duration of 6 days. All primary case-patients were males who drank tari regularly, and none had any history of drinking fresh date palm sap or exposure to sick people or animals. The six surviving case-patients were considered secondary, and all were women who did not drink tari but were exposed to the primary cases before illness.
Community investigation revealed tari production practices within both of the affected communities which could expose the sap to bat infection. Harvesters in Rangpur reported frequently observing and filtering out bat excreta with the pots used to collect the sap, and a bat roost was observed within the community. Rajshahi villagers reported no bat roosts within the district, but mentioned seeing bats landing on date palm trees. Harvesters from both communities reported use of the same collection pot for several days without cleaning to allow for the formation of yeast.
These findings and previously reported data led the researchers to suspect tari consumption as the initial route of transmission in these cases. Further, they advocated interventions already shown to limit bat exposure to date syrup, such as the use of bamboo skirts that cover the shaved portion of the tree and the collection bucket.
“A total of 55 newly described viruses from seven virus families were recently identified in urine and saliva from Pteropus spp. bats in Bangladesh, suggesting that these bats could also contaminate tari with other viruses that could cause disease in humans,” the researchers wrote. “Consumers of fermented drinks and other date palm products that are harvested using similar processes as in Bangladesh might be at risk for NiV infection and other bat-borne diseases.” – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.
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