Guinea identified the Ebola virus Saturday as the source of a highly contagious epidemic raging through its southern forests, as the death toll rose to 59.
Experts in the west African nation had been unable to identify the disease, whose symptoms—diarrhoea, vomiting and bleeding—were first observed six weeks ago, but scientists studying samples in the French city of Lyon confirmed it was Ebola, the Guinean health ministry said.
"The Ebola fever epidemic raging in southern Guinea, including the prefectures of Gueckedou and Macenta, since February 9 has left at least 59 dead out of 80 cases identified by our services on the ground," said Sakoba Keita, the ministry's chief disease prevention officer.
"We are overwhelmed in the field, we are fighting against this epidemic with all the means we have at out disposal with the help of our partners but it is difficult. But we will get there," he told AFP.
To date, no treatment or vaccine is available for Ebola, which kills between 25 and 90 percent of those who fall sick, depending on the strain of the virus, according to the World Health Organisation.
The disease is transmitted by direct contact with blood, faeces or sweat, or by sexual contact or unprotected handling of contaminated corpses.
Medical aid group Doctors Without Borders (MSF) said in a statement it would strengthen its team of 24 doctors, nurses, logisticians and experts in hygiene and sanitation already in Guinea.
The organisation has set up isolation units for suspected cases in the southern region of Nzerekore and is looking for people who may have had contact with the infected.
"These structures are essential to prevent the spread of the disease, which is highly contagious," said MSF tropical medicine adviser Esther Sterk said.
"Specialised staff are providing care to patients showing signs of infection."
MSF said it was sending around 33 tonnes of medicines and isolation, sanitation and protective equipment in two planes leaving from Belgium and France.
Ebola, one of the world's most virulent diseases, was first discovered in the Democratic Republic of Congo (DRC) in 1976 and the country has had eight outbreaks.
The most recent epidemic, in the DRC, infected 62 people and left 34 dead between May and November 2012, according to the country's health ministry.
There are fears it could be used in a biological weapons attack.
According to researchers, the virus multiplies quickly, overwhelming the immune system's ability to fight the infection.
The French embassy in the Liberian capital Monrovia released a travel advisory warning French citizens against travel to the affected parts of Guinea or areas of northern Liberia near the border between the countries.
It said anyone who had to travel to southern Guinea should "strictly respect the hygiene rules, not consume the meat of animals killed by hunting and stay away from areas of high density of population like markets and football grounds".
A medic in Monrovia told AFP on condition of anonymity that Liberia was at considerable risk from the disease.
"We have a 90 percent chance of having cases in Monrovia because about 80 percent of goods on the Liberian market come from Guinea," he said.
Ebola: profile of a prolific killer
The Ebola virus plaguing Guinea is one of the deadliest known to man, claiming the lives of three-quarters of the people it has infected so far, according to the west African nation's health ministry.
The tropical virus can fell its victims within days, causing severe fever and muscle pain, weakness, vomiting and diarrhoea—in some cases shutting down organs and causing unstoppable bleeding.
No medicine or vaccine exists.
Of around 1,850 people diagnosed with Ebola haemorrhagic fever since the virus was first identified 38 years ago in the Democratic Republic of Congo (then Zaire), 1,200 have died, the UN health agency says.
Experts say the virus, despite being extremely virulent, is containable because it kills its victims faster than it can spread to new ones.
The incubation period between exposure and the first symptoms varies from two to 21 days.
There are five species of the virus, of which three are particularly dangerous with fatality rates from 25 to 90 percent, according to the WHO.
It is transmitted through contact with the blood, body fluids, secretions or organs of an infected person.
The virus has been known to spread at burials where mourners touch the body, but doctors and nurses have also fallen ill after failing to take adequate precautions.
Even testing blood specimens for the disease presents "an extreme biohazard risk", states the WHO, and is done only in the strictest containment conditions.
People have contracted the virus after handling infected chimpanzees, gorillas, monkeys, forest antelope and porcupines, dead or alive, in the Ivory Coast, Congo and Gabon.
Named after a small river in DR Congo, the virus killed 37 people in western Uganda in 2007 and at least 170 in the north of the country in 2000.
In a new outbreak, 59 people have died in the last six weeks in the southern forests of Guinea.
The only approach for the moment is to isolate patients and promptly bury the dead, said the WHO.
Hospital staff should use gloves, masks and goggles, and disinfect religiously.
"Several potential vaccines are being tested but it could be several years before any is available," says a WHO factsheet.
"A new drug therapy has shown some promise in laboratory studies and is currently being evaluated."
The virus's natural reservoir animal, possibly the bat, is believed to reside in rain forests in Africa and areas of the Western Pacific.