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.
Officials fear west Nile might be just the first, if not ultimately the most catastrophic, of a host of deadly animal or insect-borne diseases to arrive here with global warming.
The disease, which usually causes no obvious or only mild symptoms, does not spread from person to person, but governments in many countries are extremely worried about it becoming endemic, with serious consequences for public health.
It can spread through blood transfusion although tests are in place for blood from British donors who have been to the US and Canada from the beginning of June to November.
Neither person who returned to Ireland with the disease this month had to go into hospital. One is said to be fully recovered and the other is getting better. Both are "mature" adults. Their sex, home towns, or where they visited in the Algarve were not revealed.
Paul McKeown, a specialist in public health medicine at the National Disease Surveillance Centre in Dublin, said the authorities there had been expecting the first travel-related problems with the virus to be reported in visitors to the US, with which many Irish families have extremely close ties. But there were suggestions movements of mosquitoes may be changing too.
"The likelihood is this is more of the background noise that has been grumbling away for the last few decades, but it may be harbinger of something different. We don't know yet."
Dr McKeown added: "People should enjoy their holidays as normal. The best way to protect against west Nile virus is to protect yourself against mosquito bites. Travellers should note that mosquitoes carrying the virus are most active at dawn and dusk."
The advice given stresses that where possible, people should avoid areas near water where mosquitoes are most likely to be present. Long sleeves, long trousers, socks and closed shoes should be worn and mosquito repellents used.
Indoors, screens, nets and air conditioning can be used to reduce the possibility of insect bites. Similar warnings were issued later by the Health Protection Agency in Britain. Dilys Morgan, an expert on the virus in the UK, said: "Although these are the first cases we are aware of having been contracted in the Algarve, there have been sporadic clusters of the virus in a number of European countries in recent decades. However, the risk of humans being infected in Europe is still thought to be extremely low."
People over 80 are at highest risk of death-threatening complications from the disease when it spreads to humans, but this happens in probably fewer than 1 in 100 cases. Over-50s are more prone to developing symptoms than younger people and severe disease is virtually unknown in children.
Most who catch it will never display symptoms, although one in five may develop flu-like illness with headaches, tiredness, aches and pains or rashes. Mild cases recover quickly with simple cold and flu treatments.
GPs and other doctors in Britain have for two years been warned to watch for signs while surveillance of birds and mosquitoes has been stepped up.
Contingency plans say Britons in infected areas would have to cover up routinely against bites, put screens in their homes, regularly spray themselves with repellent and empty ponds, water butts or other breeding grounds for the insects.
Last year 264 people died from the disease in the US alone and nearly 10,000 cases were reported, just four years after its arrival on the North American continent. Many times that number are likely to have been infected without symptoms. So far this year there have been four deaths among 182 cases, but the peak season is only just under way.
The virus was first isolated from a woman with fever in the west Nile district of Uganda in 1937 but it was only blamed for human illness in Israel 20 years later.
Last year one travel-associated case was reported in the Netherlands and two people in southern France either caught it locally or while visiting northern Spain.
