Health experts are closely monitoring two people who came into contact with a man who is suffering from a potentially deadly viral disease.

The 38-year-old patient remains in a critical condition on a specialist hospital unit after contracting Crimean-Congo haemorrhagic fever (CCHF).

He was diagnosed with the infectious disease when he returned to Glasgow on a flight from Kabul, Afghanistan, on Tuesday. It is the first laboratory-confirmed case of CCHF in the UK, according to the Health Protection Agency (HPA).

The man had flown into Scotland on a connecting flight from Dubai and concerns have been raised for people who were sitting close to him on the journey. NHS Greater Glasgow and Clyde said it has identified and contacted four passengers who may have had contact with the patient.

The health board said two of those - one who remained in "close proximity" to the ill man during the flight - will be monitored on a daily basis for the next two weeks for any developments of relative symptoms. The other two passengers do not require follow-up surveillance and the risk to all other passengers on the flight from Dubai is "extremely low", it added.

In a statement, the board said: "In total therefore we are currently following up two passengers from the flight with daily monitoring as a precaution for two weeks - two weeks is the maximum incubation period for the disease."

The ill man was being treated in isolation at Gartnavel General Hospital's Brownlee Centre, which specialises in infectious disease. But on Friday he was flown from Scotland to a high-security infectious diseases unit at London's Royal Free Hospital with the support of the Scottish Ambulance Service and the RAF.

The hospital houses the national specialist centre for the management of patients with hazardous infections.

Dr Syed Ahmed, NHS Greater Glasgow and Clyde's consultant in public health who is co-ordinating investigations into the case, said: "The risk of person-to-person transmission of Crimean-Congo viral haemorrhagic fever is extremely low as it can only be transmitted by direct contact with infected blood or body fluids.

"It is not a virus which is transmitted through the air. As such, the risk to those who were in close contact with him is minimal. We have already made contact with all the patient's close contacts and they are being followed up appropriately. The decision to transfer the patient to the high-security unit at the Royal Free was taken in line with the national protocol for the management of cases such as this."