An outbreak of Ebola virus in West Africa is "one of the most challenging outbreaks" the World Health Organization has ever faced, in part because the spread of false rumours is making it difficult to calm fears.

The United Nations group told reporters Tuesday that Guinea appears to be the epicentre of this latest outbreak, with at least 157 cases that have led to 101 deaths. Only 67 of those cases have been laboratory confirmed, the WHO noted in a teleconference.

The neighbouring country of Liberia has seen 21 suspected cases, leading to seven deaths. Only five of those cases have been confirmed, all in patients who had died.

Dr. Keiji Fukuda, assistant director-general for Health Security at WHO, says what makes this outbreak so challenging is that neither Guinea nor Liberia have seen Ebola before. What's more, the cases have been dispersed across a large geographical area.

The other challenge, Fukuda said, is that the outbreak has generated a great deal of fear among local populations, leading many to avoid seeking a diagnosis for what is more often than not a fatal illness.

The death rate for the strain of Ebola in Guinea and Liberia is as high as 90 per cent. There is no vaccine against it and no specific treatment. Medical staff can only attempt to manage the intense fever that the illness causes, and treat the dehydration brought on by the vomiting and diarrhea.

With so many deaths, fear has allowed the spread of rumours and misinformation. There are reports, for example, of SMS messages circulating Guinea that a medical researcher in Senegal has found the cure for Ebola - hot chocolate, Nescafe, and raw onions taken once a day for three days.

There is also an erroneous report that workers with the medical charity Medecins sans Frontières (MSF) are responsible for bringing the virus to the country.

Reuters reports that an angry mob in the Guinean town of Macenta recently attacked an MSF clinic, forcing it to shut down.

"Rumours can be harmful, if they think for example that eating onions can protect them," Fukuda told a news briefing from Geneva. "That makes it less likely they will follow infection control measures."

The WHO's Dr. Stéphane Hugonnet, who recently returned from fieldwork in southeast Guinea, says the WHO is concerned for now with identifying and tracking suspected cases, ensuring the patients are treated in clinical settings and monitor their close contacts for symptoms.

He said while cases have been confirmed in multiple areas, offocials have been able to trace transmission chains for most of them, including a couple of cases in the capital of Conakry.

Ebola is spread through direct contact with the blood, secretions, or other bodily fluids of infected people. Health-care workers are at his risk of contracting the illness if strict infection control precautions are not strictly practised.

“Ebola is clearly a severe disease,” Fukuda said. ”But it is also an infection that can be controlled,” provided the correct public health precautions are taken.

When asked how long the outbreak might last, Fukuda responded it is clear it is not yet over.

"We fully expect to be engaged in this outbreak over the next two, three, four months before we are comfortable that we are through it," he told the briefing.