India's largest state Uttar Pradesh, has had the sharpest rise in infections which has ignited fears of the return of a disease the country had almost eradicated.

Health officials are now facing the possibility of the disease spreading across the country, and are planning to relaunch an extensive immunization drive in Uttar Pradesh.

Of the 416 cases of polio reported this year, 358 cases were from the poverty-ridden state, where a combination of poverty, illiteracy and superstitious beliefs has resulted in hundreds of children without immunization.

The virus has now spread to 41 of the 70 districts in the state and neighbouring Bihar has had 28 infections.

The disease, which attacks children under five years, usually through contaminated drinking water, affects the nervous system and can result in paralysis.

India now has almost one-third of the total 1,449 cases in the world, and is being viewed as a stumbling block in the struggle against polio.

Four new cases of polio have recently been detected in New Delhi, and all four were children who had migrated to the Indian capital from Uttar Pradesh.

Polio has also re-surfaced in the neighboring states of Punjab and Haryana, and as far afield as Maharashtra due to workers migrating from Uttar Pradesh.

Experts say the virus has now travelled out of the region and is afflicting children in the whole of northern and western India and are blaming migrants for the spread of the virus.

To spread, the virus needs a lack of nutrition, and poor hygiene and sanitation, and almost all the cases have been from areas where sanitation is an issue and from poor families unable to give them a nutritious diet.

Experts say that while in developed countries, a child needs three doses for immunisation, in India, a child may need up to 10 doses.

One child in Delhi has reportedly contracted the virus despite being given nine shots of the vaccine.

Last year, only 66 cases of polio were recorded in India and the current situation is causing great concern.

Before a World Health Organisation (WHO) global anti-polio campaign in 1988, there were more than 350,000 cases worldwide, but in much of the world today the disease has been eradicated.

A strain of the disease, which originated in Uttar Pradesh state, has also travelled to the neighbouring countries of Nepal and Bangladesh and has infected people in Angola, Namibia and Congo.

India has drawn sharp criticism from international health groups for the slide back.

The World Health Organization has identified India, Pakistan, Nigeria and Afghanistan as the countries where the disease is yet to be controlled.

Bangladesh reported nine new cases of the disease this year.

India's health ministry has now set a new deadline of 2007 for ending polio in the country.

The World Health Organisation says India's failure to contain the virus is cause for serious concern and has written to India's health minister, seeking a meeting with him.