An emergency polio vaccination programme has been launched in Burkina Faso and Niger after a new case of the disease was discovered in Burkina Faso.

The World Health Organisation is to vaccinate half a million children along both sides of the border between the two countries in what they are calling a "mop-up" operation.

WHO says the vaccinations can be carried out within a couple of days.

Levels of the disease have been at their lowest in recorded history. Just 537 cases were reported world-wide last year.

The newly-discovered case of polio is the first for four years in Burkina Faso, according to the WHO.

And only one case can jeopardise all efforts and gains made so far.

Dr Chantal Kambire, WHO

The country had success in eliminating new cases of the disease after a vaccination campaign launched seven years ago, in which 2.5 million children were immunised.

Cross-border transmission

The case just discovered involved a child who had crossed into Burkina Faso from Niger with its family, WHO said.

Countries where polio is endemic

India Pakistan Nigeria Afghanistan Niger Somalia Egypt Angola Ethiopia Sudan

Christine McNab of WHO in Geneva told BBC News Online that the child had entered the country for medical treatment, because the nearest health facilities were in Burkina Faso.

Polio is a crippling, often fatal, disease whose victims can end up with twisted and useless limbs.

It invades the nervous system and can cause paralysis in a matter of hours according to the international Polio Eradication campaign.

The disease has been eradicated in much of the world but a number of African countries are still affected.

Conflict obstructs immunisation

Niger is one of just 10 countries worldwide in which a "wild virus" spreading polio is still known to exist.

Wild viruses are those which circulate among populations and are not a result of vaccination - according to Christine McNab of WHO one in 2.5 million vaccinations can result in infection.

The wild viruses exist in Niger, Nigeria, India, Pakistan, Afghanistan, Somalia, Egypt, Angola, Georgia and Zambia. In Georgia and Zambia, the virus was imported from elsewhere.

The Zambian cases in December 2001 resulted from transmission from Angola.

Areas of conflict - such as Angola, Somalia and Afghanistan - are problematic for polio control because of the difficulties in running successful immunisation campaigns.

But the WHO says it has concluded a vaccination campaign in Angola, DR Congo, Congo (Brazzaville), Namibia, Zambia, Gabon and Sao Tome.

The WHO is positive about the chances of eradication of the disease in Africa.

No new cases have been reported in Sudan and Ethiopia for over a year and Angola has not reported any for almost as long.

In some areas of the world, fears about the effects of immunisation have led to resistance to vaccination.

In Nigeria in June, Muslim clerics opposed a WHO vaccination campaign because they said they feared for the safety of children who were treated.

Vaccination has been a great success across Africa

Their fears arose from a meningitis drug trial in northern Nigeria in 1996 which killed 11 and left 200 others disabled.

Nigeria is one of the highest risk countries for polio.

Campaigns

Dr Chantal Kambire of WHO in Ouagadougou is concerned about the new case found in Burkina Faso.

"We were in that phase when a country, after a given number of years, could be declared free of polio.

"And only one case can jeopardise all efforts and gains made so far."

The WHO is hoping to stop transmission in Africa by the end of the year and eradicate the disease worldwide by 2005.