The condition of an aid worker suffering from the highly infectious Lassa Fever has deteriorated.

Doctors treating Ian Janeck say he is now fighting for his life after developing a chest infection. Previously his condition had stabilised.

Mr Janeck caught the virus while working in Sierra Leone.

He is being treated in an isolation unit at the infectious diseases centre at Coppetts Wood Hospital in north London.

A statement from the Royal Free Hampstead NHS Trust said: "The condition of the man has deteriorated and is giving cause for concern.

"Although the patient responded to anti-viral therapy as soon it was started over a week ago, he developed respiratory disease and had to be put on a ventilator.

"He has now developed a chest infection."

Mr Janeck, in his early fifties and from Chatham in Kent, was working on a contract for the Department for International Development in the West African state.

He was flown by air ambulance from Freetown, the capital of Sierra Leone, earlier this month with suspected malaria or typhoid, but was finally diagnosed as having Lassa fever after a battery of specialist tests.

Only 12 cases of Lassa fever have been diagnosed in North America and Europe since the virus was identified 30 years ago.

Victims of the rare virus suffer a high fever, headaches, diarrhoea, brain inflammation, nausea and internal bleeding. Anti-viral drugs can help but there is no cure and one in five victims dies.