Nipah Virus Risk in Raw Date Palm Sap: Symptoms, Spread and Precautions

In winter rural Bangladesh turns to fresh date palm sap. Drunk raw, it can carry Nipah virus, which made caution essential as the sap season began in December 2025. According to the World Health Organization (WHO), Bangladesh sees Nipah outbreaks almost every year between December and May, while sap is harvested in the country from November to March.

Nipah is a zoonotic virus: it passes from animals to people, and can also spread through contaminated food and directly from person to person. A health message from the Institute of Epidemiology, Disease Control and Research (IEDCR) notes that the disease was first identified in 1998-99 in the village of Sungai Nipah in Malaysia, which gave the virus its name. It was first recognised in Bangladesh in 2001. A 2023 WHO report said annual case numbers in the country had ranged from zero to 67, the peak in 2004.

WHO estimates the case fatality rate at 40 to 75 percent. The natural hosts are fruit bats of the genus Pteropus, which carry the virus without falling ill. In Bangladesh the species involved is the large Indian flying fox, Pteropus giganteus.

Sap collects overnight in pots tied to the trees. Bats drink from them and can contaminate the sap with saliva, urine or droppings. The national Nipah guideline identifies two main routes of human infection in Bangladesh: drinking raw sap contaminated with the virus, and close contact with an infected patient. Eating fruit partly eaten by bats, or close contact with infected pigs, can also transmit it.

In an outbreak in Basail, Tangail, between December 2004 and January 2005, 12 people fell ill and 11 died. The study, published in Emerging Infectious Diseases, found that 64 percent of patients had drunk raw sap, against 18 percent of the healthy people they were compared with. WHO says that from 2001 to 2008 around half of the cases in Bangladesh came from caring for infected patients.

Symptoms usually appear 4 to 14 days after infection, although incubation periods of up to 45 days have been reported. The national guideline puts the median at 7 days after a single drink of raw sap.

Early symptoms include fever, headache, muscle pain, vomiting and sore throat. These can be followed by dizziness, drowsiness, confusion and signs of brain inflammation, or encephalitis. Some develop pneumonia and severe breathing problems. In severe cases seizures occur and the patient can fall into a coma within 24 to 48 hours. About 20 percent of survivors are left with lasting neurological problems such as seizures or personality changes.

The infection is confirmed by an ELISA test for IgM antibodies in blood or cerebrospinal fluid (CSF), and by RT-PCR testing of throat swabs, urine or CSF. There is no specific drug or vaccine for Nipah; treatment is intensive supportive care for the breathing and neurological complications.

The advice of IEDCR, the national guideline and WHO:

• Never drink raw date palm sap. Boiled sap, date molasses (gur) and cooked sap desserts such as payesh are safe; IEDCR says the virus is destroyed at 70 degrees Celsius or above.
• Wash fruit thoroughly and peel it where possible; throw away fruit that bats have bitten or partly eaten.
• Cover the shaved surface of the tree and the collection pot with a bamboo or polythene skirt. In a study published in PLoS ONE in 2012, bats reached the sap on only 2 percent of nights at protected trees, against 83 percent at uncovered ones.
• Wash hands well with soap and water after contact with a patient, keep at least an arm's length away, sleep in a separate bed and keep the patient's belongings apart.
• Take anyone with signs of Nipah to the nearest government hospital without delay.

Photo: Azaman666 / Wikimedia Commons (CC BY-SA 4.0)

Sources: Jagonews24, World Health Organization (Nipah virus fact sheet; Nipah virus infection in Bangladesh outbreak report, February 2023), IEDCR (Nipah health message), Directorate General of Health Services (National Guideline for Management, Prevention and Control of Nipah Virus Infection), Emerging Infectious Diseases (Luby et al., 2006), PLoS ONE (Khan et al., 2012)