A man reads a newspaper with a headline announcing the Nigerian government's efforts to screen for Ebola in Lagos. Picture: Pius Utomi Ekpei

London - An outbreak of Ebola could spread worldwide after an infected passenger plane introduced the deadly virus to Nigeria, health experts warned on Sunday night.

Previous outbreaks were confined to forests and rural areas, but this one has already spread across four countries in West Africa and has killed 672 - the disease’s biggest death toll.

The news came as it emerged that an American doctor working for a charity in Liberia had become infected.

Dr Kent Brantly, 33, from Texas, had moved to the country for the Samaritan’s Purse organisation with his children and wife, Amber, to help contain the disease.

More than 1 000 others have been infected by the virus, which can go unnoticed for three weeks and kills 90 percent of victims. The outbreak started in Guinea in February and spread to neighbouring Liberia and Sierra Leone in weeks.

After an air traveller brought it to Nigeria, health experts now fear infected air passengers who do not realise they have the virus could spread it around the world.

With 170 million people, Nigeria is Africa’s most populous nation and airlines fly from there to Britain, other European countries and North America.

Civil servant Patrick Sawyer collapsed at Lagos Airport in Nigeria on July 20 after flying in from Liberia, where he had attended the funeral of his sister, who had also succumbed to the disease.

His plane also landed in Togo on its way to Nigeria, prompting fears that the virus may have also reached a fifth country. Professor Hugh Pennington, emeritus professor of bacteriology at the University of Aberdeen, said: “If the disease gets going in Nigeria, it would be cause for concern.

“Nigeria has close links with the UK and many other countries.”

Nigeria, Guinea, Liberia and Sierra Leone are now screening air passengers - but doctors say this may not be effective because Ebola has an incubation period of two to 21 days and cannot be diagnosed on the spot.

Symptoms include high fever, bleeding and damage to the nervous system. There is no vaccine or cure. It is spread by contact with infected blood or other bodily fluids.

All outbreaks since 1976, when Ebola was first identified, have been in Africa, with the previous highest death toll being 280. - Daily Mail