The N.Y. Times reports that Bangladesh is suffering an outbreak of deadly Nipah virus, causing the government to adopt an unusual prevention tactic: a ban on the sale of fresh palm sap.

The virus, carried by bats, was identified only in 1999. It causes dangerous brain inflammation in humans and is infectious. The Bangladeshi outbreak is unusually lethal, killing 35 of the 40 people known to have been infected.

The first known outbreak of Nipah virus was in Malaysia, where most victims raised or butchered pigs that were the source of infection. The pigs are believed to have rooted beneath bat colonies in trees, eating food contaminated by droppings. But the Bangladesh outbreak happened without a swine vector.

Bangladeshis like drinking date palm sap, which is gathered “in a way similar to maple syrup collection,” said Dr. Jonathan H. Epstein, a veterinarian with the EcoHealth Alliance, which is helping Bangladesh track the virus.

Gatherers called gachis climb high into the trees, shave the bark with machetes and hang clay pots on the trunks to collect the sap at night. Large fruit bats called Indian flying foxes are attracted and lap up the running sap, sometimes fouling the pots with their saliva, urine or feces.

Many people in the tropics leave palm sap to ferment into wine — and fermentation might kill the virus. But most Bangladeshis are Muslim, and do not drink alcohol, Dr. Epstein said.