The government is stepping up its surveillance for the potentially deadly West Nile virus in birds, mosquitoes and humans and preparing contingency plans for its arrival in Britain.
Officials are considering the widespread emergency use of pesticides and insect repellent against mosquitoes, the carriers of the disease, should the alarm be raised.
They are also preparing advice for medical and veterinary staff as well as a public information programme in what they still term the "unlikely event" of its arrival.
The disease does not routinely spread from person to person but there has been evidence that it can spread through blood transfusion, organ transplantation, mother's breast milk and from mother to baby in the womb.
The government already routinely uses anti-virus treatments against blood plasma imported from America, but any finding of the virus here would inevitably spark an urgent review of blood transfusion practices.
The big increase in planning in recent months indicates just how seriously the threat of importing this and other diseases is being taken. Professor Sir Liam Donaldson, the chief medical officer, has made strengthening public health defences a priority.
The disease has infected more than 4,000 people in the United States since 1999, killing 272, and there have been outbreaks in humans and horses in parts of Europe since the 1960s. Most recent epidemics were in Bucharest, Romania, in 1996, Volgograd, Russia, in 1999, and in Israel in 2000.
The Department of Health is funding Durham University to assess the distribution of mosquito species across central and southern England and test mosquitoes caught in this survey for the virus. Testing of dead birds is to be increased while horses are also to be checked more rigorously for infection.
A paper to a European Commission veterinary committee last month suggested that the horse survey might be targeted on wild herds. No evidence of the disease has yet been found in surveys of more than 650 dead birds, up to 400 live birds or in humans who suffered unexplained cases of brain inflammation, encephalitis.
Doctors will soon be warned again to look out for unexplained disease this year, particularly among people over 50, where the disease is more likely to be fatal.
Previous cases in Britain have only been among travellers and most people infected do not even display symptoms. These usually include fever, headache or body ache, but a few patients develop a more serious condition.
Birds are thought to be the main host for the disease which is spread by mosquitoes feasting on their blood. The mosquitoes then infect animals and humans. But research in the US has still not provided proof of this despite incidence of human disease being highest in states where most dead birds have also been found.
The disease was first identified in the West Nile district of Uganda in 1937 and linked to brain inflammation in Israel in 1957. Species of mosquito that carry the disease are present in Britain but up to now it has been thought that they are not numerous enough to pose a danger.
It has also been pointed out that birds from parts of Africa where the disease is endemic have been regular visitors here for years without them bringing the disease with them.
Warwick University has recently completed an assessment of whether vastly increased use of pesticides to control mosquitoes would work or whether the natural environment would be put at unnecessary risk. Its verdict has not yet been made public by the Department of Health.
There has been some concern that benign insects might be destroyed by such measures. Local councils also lack experience in the outdoor spraying of large areas to combat mosquitoes in this country.
