The viral infection Japanese encephalitis has claimed more than 500 lives in Uttar Pradesh and Bihar so far this year, with children facing the brunt of the disease.

According to a union health ministry document, Uttar Pradesh is the worst affected with 23 of its districts having been declared endemic.

'Twenty-three districts of eastern Uttar Pradesh are endemic to Japanese encephalitis,' the document said, adding that till Nov 16 this year, 476 people have died due to the disease in the state.

In Bihar, the number of deaths is at least 30 this year. Over 140 are still undergoing treatment for this viral disease in the state. Besides Japanese encephalitis, both these states contribute over 90 percent of India's polio burden.

Domestic pigs and wild birds are reservoirs of the Japanese encephalitis virus. The virus is transmitted by infective bites of female mosquitoes, mainly belonging to culex tritaeniorhynchus, culex vishnui and culex pseudovishnui group.

The disease gets its name as the virus was first detected in Japan.

The ministry document said that seven districts in Gorakhpur and Basti division in Uttar Pradesh - Gorakhpur, Kushinagar, Deoria, Maharajganj, Sant Kabir Nagar, Basti and Siddarth Nagar - contribute over 90 percent of the Japanese encephalitis deaths in the state.

Official statistics said that last year 537 people lost their lives due to the disease in the state. The ministry also believes that it is children in the age bracket of one and 15 years who are facing the maximum difficulty due to the disease.

To curb the spread, the health ministry claims that it has vaccinated 83 percent of the children belonging to the high risk group in 21 of the 23 endemic districts of Uttar Pradesh.

One of the major problems facing Uttar Pradesh is wastage of vaccine due to its over-exposure to heat. This year alone, the state refused to use over a million doses of such vaccines due to the same problem.