DHAKA, Bangladesh » The government says an outbreak of the deadly Nipah virus has killed at least 15 people in northern Bangladesh in the past week.

The government’s Institute of Epidemiology, Disease Control and Research asked farmers Saturday to avoid harvesting dates or drinking date juice, a popular winter treat. The virus is usually spread by pigs and fruit bats, which feed on dates and can contaminate the fruit with the virus.

The virus causes encephalitis, which leads to inflammation of the brain. No drugs have proven effective against it, and it is fatal in about 50 percent of human cases.