The Ebola outbreak in West Africa will not be stopped unless wealthy nations intervene to contain the virus, the head of a leading a medical charity has said.

Joanne Liu, of Doctors Without Borders, said on Tuesday that authorities were "losing the battle", and that the world had ignored the gravity of the epidemic.

"Six months into the worst Ebola epidemic in history, the world is losing the battle to contain it. Leaders are failing to come to grips with this transnational threat," she said.

"The [World Health Organisation] announcement on August 8 that the epidemic constituted a 'public health emergency of international concern' has not led to decisive action, and states have essentially joined a global coalition of inaction."

Liu called for a global biological disaster response, including funding for more field hospitals, trained civilian or military medical personnel and mobile laboratories in Guinea, Sierra Leone and Liberia. 

She said in her statement that "any military assets and personnel deployed to the region should not be used for quartine, containment or crowd control measures as forced quarantines have only bred fear and unrest.

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At least 1,550 people have been killed by the disease in the three countries, including more than 120 health workers. Nigeria and Senegal have also reported deaths.

Tom Frieden, the director of the US Centres for Disease Control and Prevention, also told media on Tuesday that the outbreak was "spiralling out of control".

"The situation is bad and it looks like it's going to get worse quickly. There is still a window of opportunity ... but that window is closing, and we need to act now," he told NBC News channel.

Meanwhile, scores of health workers in Liberia's main hospital in Monrovia have gone on strike claiming they have not been paid for two months.

The protest follows a one-day strike over pay and conditions at the Connaught hospital in Sierra Leone's capital on Monday. 

Reuters also reported that staff at the main Ebola clinic in Kenema, eastern Sierra Leone, also walked off the job last week in protest at conditions. 

Meanwhile, the death toll from an outbreak of a seperate strain in the Democratic Republic of Congo as killed 31 people, the government said on Tuesday. 

The WHO said that the outbreak in northern Congo's Djera region was "distinct and independent even, with no relationship to the outbreak of West Africa".

The Zaire strain of the deadly virus is indigenous to Congo and there have been seven outbreaks in the country since it was first discovered there in the remote Equateur province in 1976.

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Source: Agencies