A rare, brain-damaging virus that experts consider a possible epidemic threat has broken out in the state of Kerala, India, for the first time, infecting at least 18 people and killing 17 of them, according to the World Health Organization.

The Nipah virus naturally resides in fruit bats across South and Southeast Asia, and can spread to humans through contact with the animals’ bodily fluids. There is no vaccine and no cure.

The virus is listed by the W.H.O. as a high priority for research. Current treatment measures are insufficient, according to Dr. Stuart Nichol, the head of the viral special pathogens branch at the Centers for Disease Control and Prevention.

“There’s a market failure for protecting people from this,” said Dr. Steve Luby, an epidemiologist at Stanford University. “It’s not like treating baldness or breast cancer, where wealthy people will pay for your product. There’s no big customer here, no incentive, until it escalates.”