(CNN) -- At least 70 people are reported to have died from Ebola hemorrhagic fever in Guinea, according to a statement from the West African nation's health ministry.
Officials say there are at least 111 suspected cases of the viral disease, which spreads in the blood and shuts down the immune system, causing high fever, headache and muscle pain. The virus is transmitted by contact with the fluids of infected people or animals.
"The priority is to isolate suspected cases," said MSF, which has set up two isolation facilities in the most affected districts, Gueckedou and Macenta, both in southern Guinea.
Four of the fatalities from the disease are in Conakry, the capital city, which is on the coast.
Genetic analysis of the virus shows that it is closely related to Zaire Ebola virus, which was reported in 2009 in the Democratic Republic of the Congo (formerly Zaire), according to the Centers for Disease Control and Prevention.
Senegal's Interior Ministry decided to close its border with Guinea until further notice to prevent the spread of the disease, according to Senegal's state news agency.
The World Health Organization says that, to date, no confirmed cases of Ebola have been found outside of Guinea, but at least 12 suspected cases are under investigation in neighboring Liberia and Sierra Leone.
Joseph Netto and Pierre Meilhan contributed to this report.