The World Health Organization says an Ebola virus outbreak in West Africa has claimed 137 lives.
The disease, typically found in central or eastern Africa, has infected people in Guinea's remote forests, its capital and in neighboring Liberia.
The widespread geography of the new outbreak has sparked fears that a new Ebola epidemic could be on the horizon, a prospect that has caused panic across a region with weak health care systems and porous borders.
In a statement posted on its website Thursday, the U.N. health agency said authorities have identified more than 220 suspected or confirmed cases of the disease in the two countries. Nearly 200 of those are in Guinea.
There is no cure and no vaccine for the disease, which causes patients to bleed internally and externally. It is highly contagious, and infected people are usually held in isolated wards.
Further stoking concerns about the possibility of a widespread epidemic, a study published in a U.S. medical journal on Wednesday found that the Ebola outbreak is from a new strain, not one imported from countries that have had epidemics in the past.
Scientists initially believed that Central Africa's Zaire strain of the virus was responsible for the outbreak. But analysis of blood samples from infected patients researchers determined that while the Guinean form of the Ebola virus (EBOV) showed a 97 percent similarity to the strain found in Zaire, now known at the Democratic Republic of the Congo, the disease was not introduced from Central Africa.
"This study demonstrates the emergence of a new EBOV strain in Guinea," wrote the group of more than 30 doctors and scientists, who published their preliminary findings on the New England Journal of Medicine website.
Ebola is thought to have originated in forest bats. It can be transmitted between humans through body contact and the exchange of bodily fluids.
"It is possible that EBOV has circulated undetected in this region for some time. The emergence of the virus in Guinea highlights the risk of EBOV outbreaks in the whole West African sub-region," the report said.
Of the 197 clinical cases of Ebola declared in Guinea, 122 people have died, including several health workers, according to the World Health Organization’s latest update, which cited Guinean health ministry figures. Sixteen of those died in the capital, Conakry.
Guinea's government had previously placed the death toll at 106. The health ministry said on Tuesday that the number of new cases had fallen rapidly and the outbreak was nearly under control.
A senior health ministry official told Reuters on Thursday the government planned to stop publicly releasing the death toll to avoid causing unnecessary panic.
In an effort to contain the epidemic, countries in the region have imposed restrictions ranging from basic health checks at airports to Senegal's decision to completely shut its land border with Guinea.
Gambia earlier this month banned aircraft bound for its capital, Bajul, from picking up passengers in Guinea, Liberia and Sierra Leone.
The European Union announced Thursday that it was increasing its aid to those providing care for Ebola patients to $1.9 million.
Al Jazeera and wire services