* Fever killed some 185 people in Guinea, Libera since March
* WHO sending in experts and essential supplies
* No new cases in Guinea capital since April 26 (Adds new figures on regional cases, details)
ABIDJAN, May 26 (Reuters) - Five people have died in Sierra Leone's first confirmed outbreak of Ebola virus, the World Health Organisation (WHO) said on Monday, signalling a new expansion of the disease which regional officials said had been brought under control.
Ebola, a haemorrhagic fever with a fatality rate of up to 90 percent, is believed to have killed some 185 people in neighbouring Guinea and Liberia since March in the first deadly appearance of the disease in West Africa.
Previously, several suspected cases of Ebola were recorded in Sierra Leone early on in the West African outbreak, but they later tested negative for the disease.
In a statement posted on its website, the WHO said the outbreak in Sierra Leone was located in an area along the country's border with Guinea's Guéckédou prefecture, where some of the earliest cases of the disease were recorded.
"Preliminary information received from the field indicates that one laboratory-confirmed case and five community deaths have been reported from Koindu chiefdom," it said.
The WHO said it was deploying six experts to the area along with essential supplies.
The West African outbreak spread from a remote corner of Guinea to the capital, Conakry, and into Liberia, causing panic across a region struggling with weak healthcare systems and porous borders.
A total of 258 clinical cases have been recorded in Guinea since the outbreak was first identified as Ebola, including 174 deaths - 95 confirmed, 57 probable and 57 suspected - according to the WHO.
No new cases of Ebola have been detected since April 26 in Conakry, where an outbreak could pose the biggest threat of an epidemic due to the city's role as an international travel hub.
However Guinean health officials announced two new confirmed cases on Friday in an area previously untouched by the virus.
The disease is thought to have killed 11 people in Liberia.
Ebola is endemic to Democratic Republic of Congo, Gabon, Uganda and South Sudan, and scientists initially believed that Central Africa's Zaire strain of the disease was responsible for the infections in Guinea and Liberia.
However researchers later published a study saying the West African outbreak was caused by a new strain of Ebola. (Reporting by Joe Bavier; Additional reporting by Tom Miles in Geneva; Editing by Alison Williams)
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