Liberia has been declared free from Ebola after no new cases were reported for over a month, the World Health Organisation has said.

Peter Jan Graaf, the head of the United Nations Mission for Ebola Emergency, urged vigilence until the worst-ever recorded outbreak of the virus was extinguished in neighbouring Guinea and Sierra Leone.

No new cases were reported in 42 days - twice the maximum incubation period for the deadly disease.

"We're proud of what we collectively managed to do but we need to remain vigilant," he said. "The virus is not yet out of the region and as long as the virus is in the region we're still all of us potentially at risk."

Medical charity Doctors Without Borders (MSF) said that Liberia's completion of the WHO's benchmark for the end of an Ebola epidemic should not lead to complacency.

"We can't take our foot off the gas until all three countries record 42 days with no cases," said Mariateresa Cacciapuoti, MSF's head of mission in Liberia.

She urged Liberia to step up cross-border surveillance to prevent Ebola slipping back into the country.

A total of 11,005 people have died from Ebola in the West African countries of Liberia, neighbouring Guinea and Sierra Leone since the outbreak began in December 2013, WHO reported.

At least 4,700 of those have been in Liberia, where the outbreak peaked between August and October, with hundreds of cases a week, sparking international alarm.

Helped by the visible US military presence, President Ellen Johnson Sirleaf's government launched a national awareness campaign to stem the infectious disease, which is spread by physical contact with sick people.

Heightened surveillance

The UN Special Envoy on Ebola, David Nabarro, said this week that Liberian authorities had pledged to maintain heightened surveillance for at least a year after being declared Ebola-free on Saturday.

Nabarro suggested that, even though fewer than 20 new cases were reported in Guinea and Sierra Leone last week, it could take months to get to zero.

International aid organisations were forced to step in as the Ebola outbreak ravaged the region's poorly equipped and understaffed healthcare systems.

MSF - which was highly critical of the slow response by the United Nations and western governments - opened the world's largest Ebola management centre in Monrovia, with a capacity of 400 beds.

According to the WHO, a total of 868 health workers have caught the virus in Guinea, Liberia, and Sierra Leone since the start of the outbreak, of whom 507 died. 

International Medical Corps (IMC), a charity that ran two Ebola clinics in Liberia, appealed for international support in rebuilding the healthcare system there in the wake of the virus.

"Now is the time to build on the momentum we have generated to strengthen the Liberian health system ... and change attitudes to keep the people of Liberia safe long into the future," said Anouk Boschma, IMC's acting country director in Liberia.

Source: Reuters