A British aid worker is seriously ill after being rushed home with the symptoms of potentially deadly Lassa fever.

The man, in his 50s from Kent, is in isolation at Coppets Wood Hospital in Muswell Hill, north London

Officials have stressed that there is no danger to the public but 90 hospital staff who have had contact with the man are being closely monitored for signs of the virus.

The man, who has not been named, is said to be critically ill but in a stable condition.

He was flown by air ambulance from the capital, Freetown last Monday to University College Hospital, London with suspected malaria or typhoid.

After tests he was diagnosed with the rare Lassa fever and initially responded to anti-viral drugs.

But his condition deteriorated after his lungs began failing on Saturday, and he is now unconscious and on a ventilator.

Dr William Weir, consultant in infectious and tropical diseases, who is treating the man, said: "He is critically ill. I spoke to his wife yesterday and she is understandably upset.

"In situations like this we have to be completely truthful with relatives and tell them exactly what the patient's future contains. His wife knows he is critically ill."

He is believed to have contracted the infectious virus while working in Sierra Leone in Africa.

Africa

Although more common in Africa, there have only been 12 cases confirmed in Europe or the US since 1970.

Its symptoms include a very high temperature - up to 41C - and in the worst cases, it can cause internal bleeding and breathing problems.

The fatality rate for those more seriously ill is between 15% and 20%.

It can be passed from person to person, although this is unlikely.

Approximately 90 people who had been in contact with the patient, including those who helped carry him back by air ambulance, have been told to check themselves for any of the symptoms.

Common in Africa

In Western Africa, there are as many as 300,000 Lassa fever infections per year, and approximately 5,000 deaths.

The man is being treated in a "negative pressure" room at the Coppetts Wood Hospital in North London.

In these rooms, the air pressure is artificially kept slightly lower than the rooms outside.

This means that any airborne viruses tend to stay within the room, as when a door is opened, air will flow inwards to equalise the pressure, rather than outwards.

A spokesman for the hospital said: "The man is strongly suspected to be suffering from Lassa fever, and is seriously ill in the high security infectious disease unit."

Cases of tropical viruses in Europe almost always originate in people who have visited areas in which the viruses are more commonplace.

Last year a man died in Germany from Yellow Fever picked up on a trip to Africa.