At least 60 people died in a recent outbreak of viral encephalitis in the eastern Indian state of West Bengal, a top health official has said.
Doctors say patients come from seven affected districts in northern Bengal.
The disease usually occurs during the monsoon season across northern India and West Bengal is normally not among the worst-affected states.
Encephalitis causes brain inflammation and can result in brain damage. Symptoms include headaches and fever.
West Bengal health official Biswaranjan Satpathy told reporters there had been a sudden spike in cases and deaths from encephalitis between 7 and 20 July and the situation had now reached “alarming proportions”.
He could not identify a specific reason for the rise.
“It wasn’t like this in June, it suddenly shot up,” Mr Satpathy said, while visiting a hospital in the town of Siliguri in northern Bengal.
“We are dedicated to this. The cases are happening and that’s why people are here. We are trying to help everyone.”
Several thousand people, mostly children, have died of encephalitis in northern India – Uttar Pradesh and Bihar – since the first case was detected in the mid-1970s.
Last month, federal Health Minister Harsh Vardhan ordered “extraordinary steps” to end encephalitis, including an immunisation drive and dedicated hospital beds for patients in affected districts.
Last year India launched a vaccine against Japanese encephalitis as part of a national programme to fight the virus.