Senegal has been declared free of Ebola after 42 days passed without a new confirmed case, the World Health Organisation has said.

"WHO officially declares the Ebola outbreak in Senegal over and commends the country on its diligence to end the transmission of the virus," the UN health agency said in a statement on Friday.

The benchmark of 42 days is twice the maximum incubation period for the disease. A similar WHO statement on Nigeria is expected on Monday after the requisite period without a new infection.

However, the WHO said the country remained vulnerable to further cases of the virus being imported.

"While the outbreak is now officially over, Senegal's geographical position makes the country vulnerable to additional imported cases of Ebola virus disease," the agency said.

"It continues to remain vigilant for any suspected cases by strict compliance with WHO guidelines."

There has been only one case in Senegal, which was non-fatal.

The WHO said on Friday that the death toll in Guinea, Liberia and Sierra Leone had risen to 4,546, with 9,191 known cases. Nigeria has recorded 20 cases and eight deaths.

Elsewhere, Spain has recorded one local Ebola infection and the US has three confirmed cases including one death.

A separate Ebola outbreak in Democratic Republic of Congo, from a different strain of the virus, has killed 49 of 68 people infected.