One of the world's greatest health achievements - the eradication of polio - may be under threat because of waning interest from donors, the World Health Organisation (WHO) has warned.

The organisation says the world could be free of polio by the year 2005 if all goes well.

But it is worried that interest is fading in wiping out the disease, which was one of the most deadly and disabling in the world before a vaccine was found in the 1950s.

It is having trouble raising funds for the final stage of eradication - targeting children in high-risk areas.

The WHO estimates it needs an extra �350m from donor countries before 2001, although the governments of the countries affected cover between 50 and 80% of the costs of vaccination themselves.

Smallpox

Health officials say eradicating polio would be the greatest health achievement since smallpox was officially wiped out in 1977.

The WHO estimates that new worldwide polio cases fell to just 3,200 in 1998.

Reported cases of the disease have dropped by 90% in the last decade after the WHO launched a worldwide vaccination campaign.

The number of people suffering from polio around the world is estimated to be around 35,000.

As many as 20m people in the world are suffering from the effects of the poliomyelitis virus, which causes paralysis and difficulties walking and breathing.

But it can be easily eradicated because it is difficult to catch. It is only spread by person to person contact and cannot live long outside the body.

Immunisation campaigns

The demise of polio is due to worldwide support for immunisation programmes and the cheapness and effectiveness of the vaccine. It costs just $3 per child.

By 1998, 118 countries had carried out at least one round of National Immunisation Days for children under five.

The only WHO region which is officially polio free is the Americas, but Europe, the Western Pacific and parts of North and Southern Africa have had no recent cases.

They will not be officially free of the disease until they have gone three consecutive years with no reported cases.

The main countries still affected by polio include South Asia and Western and Central Africa.

War and basic health infrastructure problems make it difficult to carry out immunisation problems in some countries.

In August 1998, for example, the Democratic Republic of Congo was forced to suspend its programme because of ongoing fighting.

However, in other countries affected by war temporary ceasefires have been held to enable health workers to carry out immunisation programmes.