A resurgence of the deadly polio virus in northern India is undermining global efforts to eradicate the crippling disease.
Health officials say a sudden flare-up of polio in the populous north Indian state of Uttar Pradesh is posing a danger to polio-free regions in and outside India.
India has reported more than 280 new cases of polio this year - four times more than all of last year.
Jay Wenger, the head of the National Polio Surveillance Project, managed jointly by the World Health Organization and the Indian government, says the virus is spreading to neighboring countries that had stamped out the disease.
"We know that the virus now in Nepal came from India, and the virus that they are having trouble with in Bangladesh right now also came from India," said Wenger. "Those two countries were actually polio-free for a number of years, [and] have actually had to go back and start all over again."
The setback comes at a time when health workers worldwide are waging the end game against the disease. Polio has been eliminated from most countries following a global eradication drive begun in 1988, but it survives in a handful of Asian and African countries.
India has been at the epicenter in the ambitious battle against polio because it accounted for the largest number of cases in the world.
The country made dramatic progress over the past decade, eliminating polio from most regions and reducing the number of cases to 66 last year.
But dismayed health officials now confront a huge setback as the disease resurfaces - mostly in Muslim-dominated areas in Uttar Pradesh. It is a sprawling state of 170 million people, with large pockets of great poverty.
Health officials say a key obstacle is a rumor that has swept parts of the Muslim community, saying the polio vaccine will make children sterile and is part of a conspiracy to reduce the Muslim birth rate.
Some progress was achieved in recent years after authorities sought help from Muslim clerics to dispel the rumor. But health officials say it appears that at least 10 percent of all children, mostly in Muslim-dominated areas, have missed vaccinations since late 2005.
Wenger says a combination of factors could have caused the resurgence in Uttar Pradesh.
"Probably there is some level of fatigue with the program," added Wenger. "It is possible some complacency set in. The general health care infrastructure is not so strong there, and finally there is some level of reluctance in some parts of the population to actually take the vaccine."
Polio usually strikes children under five, causing paralysis or even death. WHO has already missed two deadlines to eradicate the disease - the first in 2000 and the second in 2005.