The World Health Organisation has declared Nigeria officially Ebola-free, after 42 days - or two incubation periods - without any new confirmed cases of the deadly virus.

"The virus is gone for now. The outbreak in Nigeria has been defeated. This is a spectacular success story that shows to the world that Ebola can be contained," WHO country representative Rui Gama Vaz said in Abuja.

The arrival of Ebola in Nigeria, which is Africa's most populous country, leading economy and top oil producer, sparked fears of a rapid spread throughout its 170 million people.

But the doomsday scenario did not happen and health experts involved in tackling the outbreak praised the authorities for their rapid response and comprehensive contact tracing.

In all, eight people died out of 20 confirmed cases in Nigeria's biggest city, Lagos, and the oil hub of Port Harcourt, while nearly 900 people were monitored for signs of the disease.

Nigeria's official Ebola-free status comes after Senegal was given the all-clear on Friday.

Both countries are coming under close scrutiny from public health specialists looking to contain the spread of the disease around the world.

More than 4500 people have died and nearly 10,000 have been infected with the haemorrhagic fever, most of them in west Africa, since the start of the year.

But a number of cases outside the region, particularly in Spain and the United States, have raised fears about its wider transmission and the urgency for a more effective response.

As well as rigorous contact tracing, Nigeria introduced stringent health screening checks at all airports and sea ports for arrivals and departures.

Cameroon, Nigeria's neighbour to the east, shut its border as a precaution, but Abuja did not close its frontiers.

Travel bans were not imposed, although leading carrier Arik Air did suspend its scheduled routes to Liberia and Sierra Leone, which with Guinea have been the worst affected by Ebola.