Dakar - A regional centre is being set up in Guinea to co-ordinate the response to the worst-ever outbreak of Ebola that has killed hundreds of people in west Africa, the World Health Organisation said on Friday.
The virus, a form of haemorrhagic fever, has swept through Guinea, Liberia and Sierra Leone leaving an estimated 539 people dead, according to the latest WHO figures.
Tracking and treating the disease has been a challenge as rural populations are often highly mistrustful of foreign doctors and fail to follow their advice.
Traditional practices, which include touching the bodies of the dead at funerals, have also contributed to its spread.
"The sub-regional centre will be responsible for ensuring effective use and deployment of limited and scarce, but highly critical resources, based on prioritisation and agreed objectives," the WHO said in a statement.
It has not recommended any travel or trade restrictions be applied to the three countries.
Medical charity Doctors Without Borders, known by its French initials MSF, warned at the end of June that the outbreak was "out of control", with more than 60 hotspots.
On Friday, it said it feared there could be an increase in cases in the coming weeks in Sierra Leone, where more than 150 of its staff are on the ground.
"We're under massive time pressure: the longer it takes to find and follow up with people who have come in contact with sick people, the more difficult it will be to control the outbreak," said MSF emergency co-ordinator Anja Wolz.
"We still have no idea how many villages are affected. I'm afraid we've only seen the tip of the iceberg," she said in a statement.
The largest number of new cases and deaths attributed to Ebola and reported this week came out of Sierra Leone, where another 32 people fell sick and 15 died.
In total, Sierra Leone has seen 337 cases of Ebola and 142 deaths, while Liberia has had 142 cases, 88 of whom have died.
In Guinea, the country most badly hit by the outbreak, the WHO said on Friday that transmission appeared to have slowed, with only one new case reported in the past week.
A total of 309 people are now confirmed or suspected to have died of Ebola in the west African nation where the epidemic broke out in February.
Both MSF and the UN health agency have said the outbreak is expected to continue for several months.
'Rumours and denial'
Unicef said on Friday that widespread misconception about the disease and "occasional hostility" to health workers was also impacting their ability to contain the outbreak.
"Rumours and denial are fuelling the spread of Ebola and putting even more lives at risk," said Manuel Fontaine, the charity's regional director for west and central Africa.
"Some people still deny that the disease is real. Others believe that it doesn't have to be treated."
Ebola is a form of haemorrhagic fever, which has several species, and can be deadly in up to 90% of cases.
It can fell victims within days, causing severe fever and muscle pain, vomiting and diarrhoea - and in some cases, organ failure and unstoppable bleeding.
The virus is believed to be carried by animals hunted for meat, notably bats.
It spreads among humans via bodily fluids including sweat, so can be spread by simply touching an infected person. With no vaccine, patients believed to have caught the virus have to be isolated to prevent further contagion.
The outbreak is the first in west Africa, and the largest since Ebola first emerged in 1976 in what is now the Democratic Republic of Congo.