Health experts are warning holidaymakers to beware of a potentially deadly virus carried by mosquitoes.

Two travellers have come back to Britain from Portugal suffering from West Nile Virus, which causes ‘flu-like symptoms and which has been known to be fatal. Both the victims had been bitten by mosquitoes while holidaying in the Algarve.

The Health Protection Agency in England is urging travellers to take extra care while abroad.

Dr Dilys Morgan, an expert on the virus at the agency, said: "Although these are the first cases we are aware of having been contracted in the Algarve, there have been sporadic clusters of West Nile Virus in a number of European countries in recent decades. However, the risk of humans becoming infected in Europe is still thought to be very low. The disease is passed to humans via mosquito bites and there are precautions that people can take to prevent being bitten."

These included wearing loose-fitting, light-weight clothing that covers up skin as much as possible, staying indoors during the peak hours of mosquito feeding between dusk and dawn, and using insect repellent on exposed areas, she said.

Four out of five people who catch the disease recover with no further problems. The disease is rare in the UK, but relatively common in tropical countries and around the Mediterranean