The World Health Organisation (WHO) has called the outbreak of the deadly Ebola virus believed to have killed more than 100 people in Guinea among the "most challenging" for health workers since the deadly disease emerged four decades ago.

As the suspected death toll topped 100, WHO Assistant Director-General Keiji Fukudathe said Tuesday that the agency was concerned about the spread of the virus from its epicentre in the forests of southern Guinea.

"We have not had an Ebola outbreak in this part of Africa before," said Fukuda, whose agency has rushed scores of aid workers to the region to contain the epidemic.

"This is one of the most challenging Ebola outbreaks we have ever faced," he said.

The most severe strains have had a 90 percent fatality rate, and there is no vaccine, cure or specific treatment.

The outbreak has sparked fear in Guinea, where a mob in the south of the country last week attacked international aid workers, whom they blame for bringing the haemorrhagic fever.

"It's absolutely critical to get out as much accurate information as possible to communities and the countries affected, to reduce the rumours, so that people have facts to work with," Fukuda said.

One example of such rumours is the widespread belief that eating two raw onions a day can prevent infection.

"Ebola is clearly a severe disease. It's an infection with a high fatality rate. But it's also an infection that can be controlled," he said.

According to fresh WHO figures released Tuesday, there have been 157 suspected cases in Guinea, 101 of them fatal. Of those, 67 have been confirmed as Ebola victims by laboratory tests.

Twenty of the cases have been in the capital Conakry, a sprawling port city on Guinea's Atlantic coast and home to up between 1.5 million and two million people.

Outbreak expected to last months

“We fully expect to be engaged in this outbreak for another two, three, four months,'' Fukuda said.

The WHO has not recommended any trade and travel restrictions for Guinea.

But other countries across west Africa have been bracing against the epidemic, with Senegal closing its border with Guinea.

"We have everything in place to take measures against Ebola. We have a well-oiled system, which we are perfecting daily," Senegal's Health Minister Eva Marie Coll Seck said Tuesday after visiting the port and airport in the capital, Dakar.

The disease is a particular concern for Senegal because it is a leading tourist destination in the region, with arrivals topping one million in 2011, according to the World Bank.

In Liberia, there have been 21 cases, including 10 fatalities, of which five have been confirmed as Ebola.

There have also been two suspected cases in Sierra Leone, affecting people believed to have been infected in southern Guinea but who died over the border.

In Mali, there have been nine suspected cases, with tests so far showing two of them did not have the virus.

A suspected case in Ghana meanwhile turned out not to be Ebola.

Ebola leads to haemorrhagic fever, causing muscle pain, weakness, vomiting, diarrhoea and, in severe cases, organ failure and unstoppable bleeding.

The chances of survival increase if patients are kept hydrated and treated for secondary infections.

The virus can be transmitted to humans who handle sick or dead wild animals – believed to be its original source – and between humans through direct contact with another's blood, faeces or sweat.

Sexual contact, or the unprotected handling of contaminated corpses, can also lead to infection.

(FRANCE 24 with AFP, AP)