• Reuters in Conakry
• theguardian.com, Monday 31 March 2014 11.33 EDT

Nurses put on protective gear to treat Ebola patients in the southern Guinean town of Guéckédou. Photograph: Médecins sans Frontières/AFP/Getty Images

Guinea faces an Ebola epidemic on an unprecedented scale as it battles to contain confirmed cases now scattered across several locations that are far apart, the medical charity Médecins sans Frontières said.

The warning from an organisation used to tackling Ebola in central Africa came after Guinea's president appealed for calm as the number of deaths linked to an outbreak on the border with Liberia and Sierra Leone passed 80.

The outbreak of one of the world's most lethal infectious diseases has alarmed a number of governments with weak health systems, prompting Senegal to close its border with Guinea and other neighbours to restrict travel and cross-border exchanges.

Figures released overnight by Guinea's health ministry showed that there had been 78 deaths from 122 cases of suspected Ebola since January, up from 70. Of these, there were 22 laboratory-confirmed cases of Ebola, the ministry said.

"We are facing an epidemic of a magnitude never before seen in terms of the distribution of cases in the country," said Mariano Lugli, the co-ordinator of Médecins sans Frontières' project in Conakry, the capital of Guinea.

The organisation said on Monday it had been involved in dealing with nearly all other recent Ebola outbreaks, mostly in remote parts of central African nations, but Guinea is fighting to contain the disease in numerous locations, some of which are hundreds of miles apart.

"This geographical spread is worrisome because it will greatly complicate the tasks of the organisations working to control the epidemic," Lugli added.

The outbreak of Ebola – a virus which has a fatality rate of up to 90% – has centred on Guinea's south-east. But it took authorities six weeks to identify the disease, allowing it to spread over borders and to more populated areas.

Cases were confirmed in Conakry last week, bringing the disease – previously limited to remote, lightly populated areas – to a sprawling Atlantic Ocean port of two million people.

Guinea's president, Alpha Condé, appealed for calm late on Sunday. "My government and I are very worried about this epidemic," he said, ordering Guineans to take strict precautions to avoid the further spread of the disease.