Ebola has killed at least 59 people in Guinea and there are fears the virus may have spread to neighbouring Sierra Leone, world health officials have said.

Cases of the disease, which can kill 90 percent of those infected, have been registered in three southeastern towns and in the Guinean capital, Conakry, since Februrary 9. They are the first recorded cases in the country.

"It is indeed Ebola fever. A laboratory in Lyon, France, confirmed the information," Damantang Albert Camara, a government spokesman, told the Reuters news agency.

EBOLA A highly virulent form of haemorrhagic fever. Can kill up to 90 percent of those infected. Symptoms include fever, diarrhoea, vomiting and bleeding. Can be caught through close contact with wildlife. Passed between humans through fluids.

Dr Sakoba Keita, who leads the epidemics prevention division at Guinea's health ministry, said that officials had registered 80 suspected cases of the disease, including 59 deaths.

"But you have to understand that not all the cases are necessarily due to Ebola fever. Some will have other origins, including a form of severe dysentery," Keita said.

Officials from the World Health Organisation said that cases showing similar symptoms - fever, diarrhoea, vomiting and bleeding - had also been reported in an area of Sierra Leone near the border with Guinea.

Sierra Leone's chief medical officer, Dr Brima Kargbo, said authorities were investigating the case of a 14-year-old boy who died in the town of Buedu in the eastern Kailahun District.

The boy had travelled to Guinea to attend the funeral of one of the outbreak's earlier victims.

Kargbo said a medical team had been sent to Buedu to test those who came into contact with the boy before his death.

Medical teams sent

The international medical charity, Medecins Sans Frontieres, announced on Saturday it was reinforcing its medical and logistics teams in Guinea in response to the outbreak.

It was also flying in 33 tonnes of medicines and equipment and setting up isolation units in the three affected towns in Guinea.

"These structures are essential to prevent the spread of the disease, which is highly contagious," Dr Esther Sterk, the group's tropical medicine adviser, said in a statement.

Humans can catch ebola through close contact with infected animals including chimpanzees, gorillas and monkeys. The disease also spreads easily between humans.

It is most commonly found in the Democratic Republic of Congo, Uganda, South Sudan and Gabon.