A child found paralysed by polio in Darfur on May 20 was confirmed to have a form of the virus closely linked to the one that is endemic in northern Nigeria, the WHO said in a statement.

Until the new case, polio had not been seen in Sudan for at least three years following successful mass vaccination campaigns.

"Epidemiologists of the Global Polio Eradication Initiative have today issued a stark warning that west and central Africa is on the brink of the largest polio epidemic in recent years," the statement said.

The disease had spread through neighbouring Chad in recent months, and transmission of the wild polio virus in the region "continues to accelerate at an alarming rate", it added.

"What this adds up to is a virus and an epidemic that is gathering speed rather than slowing down at the end of the low season," WHO polio expert Bruce Aylward told journalists.

Health experts fear that thousands of African children could be paralysed for life if a major epidemic takes hold in the autumn "high season" for polio.

"There is no question that the virus is spreading at an alarming rate," said David Heymann, the WHO's polio eradication chief.

But the global drive against the disease has been thwarted by the refusal of authorities in Kano, northern Nigeria, to allow polio immunisation and local fears about the safety of the vaccine, opening up a gaping hole in the WHO's effort.

That has led to 257 cases in Nigeria so far this year, almost five times the number of cases in the same period last year, according to the latest WHO data.

It includes 60 new cases in the space of a week in March and April, the largest number recorded in such a short space of time in any country in recent years, according to WHO.

The alarm has also been raised because of the accelerating spread across the border into lowly-immunised neighbouring countries, where 40 cases have been confirmed this year spanning as far south as the Central African Republic and Botswana, and as far west as Sudan.

"This has placed approximately 74 million children at risk of polio," Heymann told journalists.

WHO urged 22 countries in Africa to hold a massive vaccination campaign in October and November to set up an "immunity barrier" around the epicentre of the epidemic in Kano and to stop the import into countries further afield.

"This is going to require an additional 100 million dollars over the next two years, including 25 million by August if we are to limit the damage," Aylward said.

WHO officials are in regular contact with Kano's governor to try to spur on immunisation there, and said most of the concerns about the vaccine have now been resolved.

An Indonesian polio vaccine which is acceptable to local leaders has been stockpiled in the region, but immunisation has not yet restarted despite optimistic signs from local authorities, Heymann indicated.

Local radical Islamic preachers had accused Washington of lacing the original vaccine with hormones designed to render African girls infertile as part of a plot to depopulate the developing world.

UN experts dismissed the charge.

But they admitted Tuesday that the suspicions about immunisation had also spread into Niger, Burkina Faso and Chad, and needed to be countered.

"We hope that once a clear strong explicit message comes from the leaders of northern Nigeria, this problem will be greatly diminished," said UN Children's Fund (UNICEF) deputy executive director Kul Gautam.

Health experts had reduced polio to a few dozen cases a year in Africa until a resurgence in Nigeria in 2002.

TERRA.WIRE