Malaria 'could become endemic disease in UK'

Malaria could return to Britain as an endemic disease, scientists said yesterday when they announced a plan to produce a "risk map" showing which areas were most likely to suffer an outbreak.

With millions of tourists visiting malaria-infected regions of the world, the risk of the disease making a comeback is further increased by global warming, which makes it easier for mosquitoes to breed in the UK.

Scientists at the University of Durham said that over the next two years they will produce a risk assessment to try to analyse the precise nature of the potential problem.

Rob Hutchinson, an entomologist at the university, told the annual meeting of the Royal Entomological Society in Aberdeen that nobody knew the scale of the threat except that it was getting bigger each year. "The risk of malaria returning to the UK is often said to be extremely unlikely. However, a proper risk assessment has not been attempted," Mr Hutchinson said.

"With huge numbers of people travelling to malaria-endemic countries, drug resistance among the malaria parasites, the possible effects of global warming and the presence of mosquitoes in the UK that are capable of carrying malaria, an extensive risk-assessment is now justified," he said. Higher winter and summer temperatures and rising sea levels ­ creating more brackish marshes for mosquitoes to breed ­ were adding to the risk, Mr Hutchinson said.

There are two principal forms of malaria carried by the many different species of mosquito. One is caused by the parasite Plasmodium vivax, which was once endemic to the UK, and another, more lethal form caused by Plasmodium falciparum, endemic to many tropical countries.

Britain has five species of mosquito that can carry vivax malaria, which was rife from the 16th century until the end of the 18th. It was known as the "ague" or "marsh fever". In some regions, notably marshy areas such as the Somerset Levels, the Essex and Kent coasts and the Severn estuary, the disease resulted in the tripling of infant mortality.

Mr Hutchinson said that, of the 25 million overseas visitors who came to Britain in 1999, about 260,000 came from Turkey and the countries of the former Soviet Union where vivax malaria was endemic and health care was poor.

"Countries with poor health care are very unlikely to provide effective treatment for malaria and therefore people travelling from these regions are potentially more likely to be carrying parasites," he said.

The two-year risk assessment will try to combine regional data on average temperatures and mosquito prevalence with places of residence for the 2,000 Britons each year who develop the disease following a trip overseas.

"If we get all these three factors occurring in specific areas then obviously the risks are going to be greater. To produce a risk map based on this information is the aim," Mr Hutchinson said. "Most of the data is available. We know about the people who have brought malaria back into the UK because it is a notifiable disease. We know where they have been and we know where they live, so we can plot this on a temperature map for the country and combine this with the known mosquito populations."

The most likely mosquito to carry the vivax parasite is Anopheles atroparvus. It breeds in the brackish water of coastal marshes and is capable of being active and feeding on human blood throughout the winter months.

The atroparvus mosquito has been linked with the last outbreak of vivax malaria in the UK involving people who had not travelled abroad. This was on the Isle of Sheppey in Kent in 1917-1919.

Another danger is that malaria-carrying mosquitoes will be brought in aboard aircraft returning from tropical regions where the falciparum form of the disease is endemic. The World Health Organisation has found that Britain is now the third most likely country in Europe to have airport-related cases of malaria.

Aircraft were routinely sprayed with insecticide but that did not always rid the cabins of potential malaria-carrying vectors, Mr Hutchinson said. "Searches of aircraft arriving from Africa show live insects can be imported and two live mosquitoes have been found to date," he said.

In some parts of Britain, such as Kent, about half the population say that they are regularly bitten by mosquitoes. If a tourist carrying the blood parasite were to be bitten, local mosquitoes could in theory sustain the disease.