Six more children have died of encephalitis in northern India, pushing the toll from an outbreak that erupted in late June to 151, officials said on Saturday.
"All the dead were below 10 years of age. Another 138 children are still in hospitals. Eighteen of them are in serious condition," senior health official AP Mishra said.
Indian authorities launched a massive drive to inoculate millions of children against Japanese encephalitis after an outbreak claimed about 1,400 lives in northern Uttar Pradesh state in 2005.
But officials in the state, where this year's deaths have been reported, said the current outbreak was not due to Japanese encephalitis.
"So far no child has died of Japanese encephalitis. This could be a mutant of the disease," B Nath, the state's top health official, said in Lucknow, the capital of Uttar Pradesh.
Mishra said the children had not been inoculated against encephalitis.
The outbreak usually begins with the onset of the monsoon rains between June and September. Mosquitoes carry the disease from pigs to human beings.
Japanese encephalitis also claimed 15 lives in July 2006 in India's northeast.
In an outbreak of another illness in Uttar Pradesh, 90 children died of a virus that authorities mistook for Japanese encephalitis but later identified as Coxsackie-B, named after a town in New York state where it was discovered.
The virus is characterised by fever and chest pains and can lead to inflammation of the heart and heart failure. It spreads through contaminated water.