The tropical disease you can catch in Britain

Visiting, or living near international airports can damage your health, according to a new report published by the World Health Organisation. The hazard does not come from the noise of jets alone; nor purely from aircraft falling out of the sky. There is also a risk of catching tropical diseases - especially malaria - from mosquitoes which have stowed away on intercontinental flights.

Visiting, or living near international airports can damage your health, according to a new report published by the World Health Organisation. The hazard does not come from the noise of jets alone; nor purely from aircraft falling out of the sky. There is also a risk of catching tropical diseases - especially malaria - from mosquitoes which have stowed away on intercontinental flights.

The danger has been around ever since air travel began. The phenomenon even has a name - "airport malaria": the catching of the disease by people who have never visited tropical countries but live close to, work in, or visit, airports. For 50 years or more, aircraft arriving from malaria-afflicted countries have - in theory - been sprayed with insecticides.

Nevertheless, there have been 14 such cases in Britain in the last 30 years, including seven in the last five years. In two of the British cases, severe attacks of malaria were traced to imported mosquitoes which flew six miles and eight miles into Sussex from Gatwick airport before biting their victims.

There have been 26 cases in France (the worst-affected country) since 1969; there have been two cases in Belgium in the last few months alone and a nasty, recent outbreak in Luxembourg. There have been 100 known cases in Europe and the United States in the last 30 years, leading to six deaths.

This is hardly an epidemic. However, a lengthy report published in the bulletin of the World Health Organisation (WHO) this month predicts that two new factors - both man-made - could lead to an alarming and quite unnecessary spread of airport malaria, unless airlines and governments tighten up the rules on the anti-insect spraying of aircraft.

The first new problem is global-warming, which could make the temperate climates of European countries more hospitable to the survival - even the breeding - of tropical varieties of mosquito.

The second problem is a growing consumer-resistance to the spraying of insecticides inside the passenger cabins of aircraft. A number of lawsuits have been brought against airlines in the US and Germany, complaining that the products used are dangerous to the health of humans, as well as mosquitoes.

"There is no scientific evidence whatever that this is the case. It is just an unwarranted scare," said Norman Gratz, the principal author of the article in the WHO Bulletin and one of the world's foremost experts on airport malaria.

"The problem is that the airline precautions against mosquitoes are already more haphazardly applied than they should be. This campaign against insecticides threatens to make things worse. Airport malaria is a serious problem. It is not yet a growing problem but it is a continuing problem and it need not be. We have all the knowledge we need to bring it under control."

The French government has already taken tough new measures, demanding documentary guarantees that any aircraft arriving from Africa, or any other malaria-affected country, has been "de-insected" before take-off. This follows one of the worst ever outbreaks of airport malaria, in 1994 at and around Charles de Gaulle airport in Paris (which was little reported at the time).

Six people, living near or working at the airport, were infected with the disease over three weeks. One of them died. Around 300 aircraft arrived from Africa in the period concerned. An official investigation estimated that between eight and twenty anopheline, malaria-bearing mosquitoes arrived on each African flight: in other words, up to 6,000 potentially infected mosquitoes arrived in France in 20 days.

The usual rate of malaria infection of anopheline mosquitoes in Africa is 2 per cent, suggesting that up to six disease-carrying mosquitoes a day were escaping from aircraft into airport and the surrounding suburbs.

An official in the French quarantine service said that the stricter new restrictions on airlines had been partially, but not entirely, successful.

Only three cases of airport malaria have been confirmed in France in the last five years. "The rules in place ought to mean that there are no cases at all," he said. "It is still a source of anxiety to us that isolated cases continue to occur, although there have been none in the past two years."

The situation in Britain is even less encouraging. Aircraft arriving at UK airports from tropical countries are also supposed to have gone through intensive, "de-insecting" procedures. However, according to figures published by WHO, there have been seven cases of "airport malaria" in Britain in the last five years - as many as in the previous 27 years.

A severe outbreak at Luxembourg airport in 1997 saw a woman and daughter fall ill with a virulent form of malaria, although the only foreign country they had visited was Iceland. They lived in a village one mile east of Luxembourg airport. Two years later a couple were diagnosed as having caught the disease after passing through the airport on the way to Scotland. A fifth case was confirmed in someone who had never visited the airport but lived two miles away. All the cases occurred in high summer, which may have allowed the imported mosquitoes to survive for unusually long periods.

As Dr Gratz and his two co-authors said in their WHO Bulletin article, airport malaria is "particularly dangerous" because doctors are often slow to diagnose the disease in patients who have never travelled to tropical countries.

They also outline two other, serious concerns. The first is the possibility that tropical varieties of mosquito may begin to breed in European countries if global warming raises average temperatures.

The second is that the stowaway mosquitoes may "re-infect" local types of mosquito with the disease. This could only happen if a native mosquito bit a person who had already been infected by an imported insect.

This is unlikely but not impossible. Dr Gratz, now retired, but formerly a senior WHO official, points out that malaria, far from being just a tropical disease, was endemic in Italy and the Netherlands until the 1930s.

The establishment of West Nile fever in New York and New Jersey in recent years may have originated with mosquitoes or other insects imported by air. Paradoxically, it is this outbreak, which produced a backlash against insecticide programmes (such as the the systematic spraying of trees). The popular fear of insecticides has now spread to the preventative spraying of aircraft.

Dr Gratz says that the "de-insecting" of aircraft has got a bad name because it is sometimes performed just before the plane takes off, when passengers are already in their seats. Tests by WHO had shown that the pyrethrum-based insecticides used were harmless to humans. However, spraying the passengers may not be the most effective method of de-insecting an aircraft.

WHO now advises that aircraft used on inter-continental flights should be treated with insecticides as part of their routine maintenance and that this should be "topped up" by spraying the interior just before passengers board. At that time, crucially, the overhead lockers (a frequent hiding place for mosquitoes) are still open.

"Complaints about de-insecting aircraft are utterly misplaced," Dr Gratz said. "I don't think these people understand what a serious problem accidentally imported insects can pose. If the WHO recommendations for de-insecting procedures are enforced, everyone should be happy, except the mosquitoes."