* Geographical spread of Guinea Ebola outbreak a worry -MSF
* Resist panic and rumours, president tells his nation
* Neighbours close borders, restrict travel and step up checks
* Deadliest outbreak of Ebola in years
By Saliou Samb
CONAKRY, March 31 (Reuters) - 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, medical charity Medecins Sans Frontieres said on Monday.
The warning from an organisation used to tackling Ebola in Central Africa comes after Guinea's president appealed for calm as the number of deaths linked to an outbreak on the border with Liberia and Sierra Leone hit 80.
The outbreak of one of the world's most lethal infectious diseases has spooked 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, coordinator of MSF's project in Conakry.
The organisation said it had been involved in nearly all other recent Ebola outbreaks, mostly in remote parts of central African nations, but Guinea is now fighting to contain the disease in numerous locations, some of which are hundreds of kilometres 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 - which has a fatality rate of up to 90 percent - has centred around Guinea's southeast. But it took authorities six weeks to identify the disease, allowing it to spread over borders and to more populated areas.
Cases were last week confirmed in Conakry, bringing the disease - previously limited to remote, lightly-populated areas - to a sprawling seaside capital of two million people.
Guinea's President Alpa Conde late on Sunday appealed for calm. "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.
"I also call on people not to give in to panic or believe the rumours that are fuelling people's fears," he added.
Liberia has recorded a total of seven suspected and confirmed cases, including four deaths, the World Health Organisation said. Sierra Leone has reported 5 suspected cases, none of which have been confirmed yet.
Brima Kargbo, Sierra Leone's chief medical officer, said a screening process had been introduced on the country's northern border with Guinea. Travellers are being asked where they are coming from and whether they or anyone they had been in contact with had fallen ill, he said.
Senegal, another neighbour of Guinea's, closed its land border over the weekend and has suspended weekly markets near the border to prevent the spread of the disease.
Regional airline Gambia Bird delayed the launch of services to Conakry, due to start on Sunday, because of the outbreak.
If the deaths are all confirmed as Ebola, a disease that leads to vomiting, diarrhoea and external bleeding, it would be the most deadly epidemic since 187 people died in Luebo, in Congo's Kasai Orientale province, in 2007.
Additional reporting by Stephanie Nebehay in Geneva and Umaru Fofana in Freetown; Writing by David Lewis; Editing by Tom Heneghan