DAKAR, March 24 (Thomson Reuters Foundation) - Scientists tackling an outbreak of Ebola in Guinea believe they have identified the virus as the Zaire strain, the most lethal of all that "raises the already high level of concern", according to France's Institut Pasteur.
At least 59 people have died after contracting a mystery illness in southeastern Guinea since early February. Six cases have been confirmed as Ebola, a haemorrhagic fever with a fatality rate of as high as 90 percent.
None of the suspected cases in the capital Conakry have tested positive. However, the deaths are the first confirmed from Ebola in West Africa and a suspected case reported in neighbouring Sierra Leone has raised fears the disease may spread into other nations with weak health systems.
"Preliminary sequencing of a portion of the virus is compatible with the Zaire species," experts at the Lyon-based Institut Pasteur said in a statement.
The institute believes the strain in Sierra Leone would be the same, but said further lab results were needed.
"Detection of Zaire Ebola virus raises the already high level of concern for this event," it said.
Institut Pasteur has been testing samples sent to France and has also dispatched a team to Conakry to help the government handle the crisis.
The symptoms of Ebola range from flu-like pains to internal and external bleeding caused by kidney and liver failures.
Humans can catch the disease from bats, gorillas and forest antelope and then it is spread between humans through contact with infected blood, bodily fluids and tissue.
The last major outbreak of the Zaire strain was in 2007, when 187 people died in the Democratic Republic of Congo - a case fatality rate of 74 percent.
Sakoba Keita, head of the preventative diseases department in Guinea's ministry of health, said the number of suspected cases had risen to 86 by Monday.
The government sent SMS messages to Guineans calling for calm and detailing precautions people could take against Ebola.
Over the weekend, officials dispatched specialised medical equipment, imposed restrictions on funerals and sought to contain panic to prevent Ebola from spreading.
Medical charity Medecins Sans Frontieres (MSF) said researchers are trying to find the source of the virus and understand how the Zaire strain reached Guinea from Sudan, Congo and Uganda where there are frequent outbreaks.
"Nobody has a clue how the virus arrived in Guinea," said Esther Sterk, MSF's tropical medicine adviser.
"We know the virus hides in some species of bats in between outbreaks in human hosts, so many people are looking at bats flying around Guinea."
(Additional reporting by Saliou Samb; Editing by David Lewis and Robin Pomeroy)