Nigeria has become the latest country to declare a national emergency over the deadly Ebola virus, as the World Health Organisation called the epidemic that has claimed nearly 1000 lives a global health crisis.

The WHO appealed for international aid to help afflicted countries after a rare meeting of the UN health body’s emergency committee, which urged screening of all people flying out of the affected countries in west Africa.

It stopped short of calling for global travel restrictions, urging airlines to take strict precautions but to continue flying to the west African countries hit by the outbreak.

And it called on countries around the globe to be prepared to “detect, investigate and manage” Ebola cases if they should arise.

WHO director-general Dr Margaret Chan appealed for greater help for those worst hit by the “largest, most severe and most complex outbreak in the nearly four-decade history of this disease”.

“I am declaring the current outbreak a public health emergency of international concern,” Chan said, warning of the “serious and unusual nature of the outbreak and the potential for further international spread”.

States of emergency had already been declared in the hardest hit countries of Guinea, Liberia and Sierra Leone, and Nigeria became the latest on Friday.

Two people have died there and five others have been infected.

The Ivory Coast, which neighbours Guinea and Liberia, said it was declaring a “very high” level of alert, while Benin is also investigating a suspect patient.

In the first European case, Spain is treating an elderly priest who contracted the disease while helping patients in Liberia.

Defining the epidemic a public health emergency of international concern – a label only used twice before, during the H1N1 swine flu pandemic in 2009 and last May for the re-emergence of polio – “alerts the world to the need for high vigilance”, Chan said.

The Doctors Without Borders (MSF) charity, which has warned the virus is “out of control”, hailed the move, but said there needed to be immediate action on the ground.

Ebola had by Wednesday claimed at least 961 lives and infected nearly 1800 people since breaking out in Guinea earlier this year, with 29 people dying in just two days, the WHO said.