The World Health Organisation warned that the outbreak of the Ebola virus that has killed more than 700 people in west Africa was spinning out of control as the disease’s spread outpaced efforts to contain it.

“This outbreak is moving faster than our efforts to control it,” Margaret Chan, WHO director-general, said on Friday in Conakry, the capital of Guinea, during a crisis meeting of the leaders of Ebola-hit Liberia, Sierra Leone and Guinea.

However, Dr Chan said the outbreak could still be halted. “The situation in west Africa is of international concern and must receive urgent priority for decisive action at national and international levels. Experiences in Africa over nearly four decades tell us clearly that, when well managed, an Ebola outbreak can be stopped.”

The statement suggests west Africa may have to take further measures to contain the spread of the virus, only days after Liberia and Sierra Leone declared national emergencies and called on the army to enforce quarantines in several villages.

There is no known cure or vaccine for the Ebola virus, which develops within two to 21 days of contagion. The disease, which has a 50-90 per cent mortality rate, causes vomiting, diarrhoea and internal and external bleeding.

The outbreak is the worst since the disease was first recognised nearly 40 years ago, with 1,323 cases and 729 deaths reported so far in four countries. The previous worst was in Uganda in 2000, killing 425, and the 280 victims who perished in the first known outbreak in 1976, in a remote village near the Ebola river in what is now the Democratic Republic of Congo.

“If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives, but also severe socio-economic disruption and a high risk of spread to other countries,” she said.

The WHO has called a meeting at its Geneva headquarters on August 6 to discuss the international implications of the outbreak.

The organisation has launched a campaign to raise funds to fight the outbreak, targeting as much as $100m. But so far donors have provided only a few million dollars.

The leaders of the three west African countries hit directly by the outbreak vowed on Friday to work together to prevent new cases of the highly infectious disease, stepping up their response after criticism for acting too slowly. Both nations have imposed quarantines and closed markets and schools.

Ernest Bai Koroma, president of Sierra Leone, on Thursday said that “the disease is beyond the scope of any one country, or community to defeat. Its social, economic, psychological and security implications require scaling up measures at international, national, inter-agency and community levels.”

The measures taken by Sierra Leone and Liberia over the past 48 hours are the most sweeping since the outbreak began in a remote forest region of Guinea in February, and later spread to the other two west African countries.

Medical charities have for weeks urged west African governments to step up their response to the outbreak, which some said was “out of control”.

Analysts have warned the disease could reduce economic activity in the region and could endanger food security as farmers flee the affected areas.

Foreign companies operating in the three worst-hit countries have imposed travel restrictions on their workers and evacuated some staff in a few cases. The two most important regional airlines have stopped flying to the affected countries.

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