Every year again: Alarm over West Nile virus cases

Holidaymakers heading for Europe, the US and Canada were last night warned to protect themselves against mosquito bites in a bid to keep the potentially deadly west Nile virus out of Britain.

Tourists were advised to take heightened security measures after laboratory tests confirmed two Irish tourists returning from the Algarve in Portugal had the disease.

It is thought to be the first time the disease has been confirmed in people in either Britain or Ireland, or linked to infection in the Algarve. The virus has spread across the US - where it has killed hundreds in the past four years - and Europe, prompting emergency plans to prepare for its arrival here.

The Portuguese authorities are believed to be stepping up surveillance in birds, mosquitoes, animals and humans, following the Irish cases. The advice to "cover up" against mosquitoes and avoid areas near water was issued by Irish and British health watchdogs after specialist laboratories at Porton Down, Wiltshire, confirmed the disease yesterday.

Advice about US travel has been given before but the new cases closer to home will mean far more attention being paid to the hazards of travel by doctors, public health officials and holiday companies.

Authorities insisted the advice was precautionary. Dangers of the disease spreading in their own countries, or travellers being infected elsewhere in Europe, were still regarded as extremely low.

Mosquitoes capable of transmitting the virus after catching it from sucking the blood of infected birds already exist in Britain but public health officials believe concentrations are still too small to be a hazard. However, birds here have been found carrying antibodies to the virus, suggesting they have been exposed to it.