PUNE, India (AP) _ Scientists say some of the 273 children who recently died in two southern Indian states likely had a rare virus spread by sand flies, while others may have died from a virus in the same family as Japanese encephalitis.

Scientists from the National Institute of Virology have not determined why the outbreak has been so deadly _ but a doctor from the World Health Organization blamed a combination of malnutrition and delayed medical care.

In recent months, 165 children have died in Andra Pradesh state, along with 108 in the state of Maharashtra.

Doctors had been puzzled because the cases were similar to Japanese encephalitis, a disease endemic to Asia. Yet in the recent cases the disease progressed much faster than normal, leading quickly from chills, fever and vomiting to coma and death.

Indian scientists and a WHO doctor say it appears likely there are two viruses at work, one of them called Chandipura after the region in northern Maharashtra state where it was first discovered in 1965.

It is ``very much confirmed beyond doubt'' that the outbreak in Andhra Pradesh is caused by the Chandipura virus, said Dr. A.C. Mishra, director of the National Institute of Virology. ``We still haven't confirmed the cases in Maharashtra as Chandipura virus.''

Chandipura is from the same virus family as rabies, but Mishra said they are only distantly related.

Mishra said his team is still trying to the cause of remaining cases, but that Japanese encephalitis had been ruled out.

``It spreads at a fast speed and can kill the patient in four to 16 hours,'' he said.

The WHO has said the second virus may be a member of the Japanese encephalitis family, and could be acting more quickly because the victims are so vulnerable.

``The children are from poor backgrounds in rural areas where health facilities are not that good,'' said Dr. Sampat Krishnan of WHO India. ``Their health condition before they came in (to the hospital) will determine the outcome,'' he said, adding that many were malnourished and had probably been first taken to see substandard doctors.

Krishnan said the Chandipura virus was probably spread by sand fly bites. The virus seemed much less deadly in earlier outbreaks, but Krishnan didn't describe it as mutation.

``We have a lot of newly emerging diseases these days _ diseases that were quiet earlier and are now emerging again,'' Krishnan said.

There is no vaccine or anti-viral medication for the diseases. Doctors treat patients by reducing fever and giving them plenty of fluids.

A total of 165 children have died over the past two months in Andhra Pradesh as of Thursday, said Dr. Gopal Reddy, the state's joint director for epidemics.

The death toll in Maharashtra was 108, Dr. Prakash Prabhakar Dokhey, one of the state's Health Services directors, said Thursday.