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

BBC: Tropical virus man 'fighting for life'

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.

BBC: Tropical virus man 'fighting for life'

Dr Gerard said that although his department at Gatwick regularly screened immigrants and asylum seekers for TB that they had not so far encountered any of the rarer illnesses such as Ebola or Lassa Fever, but he said they were alert to the threat.

BBC: GPs warned to be ready for smallpox