Malaria is often thought of as a tropical disease, one of concern to people in developed countries only when they jet off for exotic holidays In the past, however, malaria was a major problem in Europe, just like leprosy, typhoid and scurvy. The close living spaces of people and animals - humans often lived upstairs while their livestock lived downstairs - helped to maintain the disease, which is caused by a single-celled protozoan parasite transmitted by mosquitoes. No matter how hard people tried to swat the mosquitoes, the insects survived largely by sucking the blood of livestock.
Improved stabling and hygiene helped to combat malaria in Europe, and during the 19th century it was eradicated from Britain. A determined effort by the authorities in Romania in the late 1950s finally rid Europe entirely of the menace. More recently, however, malaria has been making a series of brief comebacks in the developed world, although this time the factors spreading the disease are as hi-tech as they once were primitive.
Aeroplanes are bringing in mosquitoes from countries where malaria is endemic and they are blamed for the modern-day phenomenon of "airport malaria". Mosquitoes, after leaving the aircraft, can transmit malaria when they strike unsuspecting people in the vicinity of the airport. It is a particular problem during the summer when mosquitoes survive more easily in the warm weather. In 1989, for example, there were five cases of airport malaria in Geneva. Five years later there were outbreaks around Charles de Gaulle Airport in Paris. People have also fallen ill with malaria close to Gatwick airport near London.
Indeed, scores of people in the United States and Europe have fallen victim to the disease in recent times. With temperatures on the rise, making previously inhospitable parts of the world more welcoming to mosquitoes carrying malaria, it raises the question of whether this deadly disease could once again take hold in parts of the world already declared malaria-free. "A mosquito can hop on a plane and emerge somewhere else as airport malaria," says David Rogers, a professor of ecology at the University of Oxford, England.
"On aircraft that leave areas with malaria, you can always find mosquitoes." According to Prof Rogers, the "really serious place" that could be a source of flights with malarial mosquitoes is Africa. While the air stewards and stewardesses may walk up and down the passenger aisle with an insecticide spray, Prof Rogers says it is difficult to totally eliminate the risk of infected mosquitoes taking a free holiday.
"Even if 99 per cent of airlines do it, the one per cent that don't could introduce malaria. It's a little bit like terrorism. The people who have to combat it have to succeed all of the time, while malaria has to succeed once," he says. "You will inevitably get airport malaria, so you should have a system in place to deal with it." Fortunately, there are reasons why malaria could struggle to establish itself in a new country, even though there might be occasional outbreaks near airports.
Among the most important factors, says Prof Rogers, is that malaria does not harm animals other than people. While the mosquitoes may enjoy feeding on other animals, these cannot become infected and so help to spread an outbreak. As a result of the disease being confined to humans, with proper detection and medical care, outbreaks can be contained. What is important, Prof Rogers says, is proper checks to ensure the number of mosquitoes entering a country is not on the increase.
"The authorities should be monitoring the number of mosquitoes in aircraft. If they see them increasing, they should be worried," Prof Rogers says. "If the baseline is 10 and it stays 10, you don't have to worry, but if it becomes 10,000 and you get malaria, you have to do something. "Monitoring is the most important thing to protect against an unquantified threat." It is vital to look at the number of mosquitoes travelling per aircraft and the number of aircraft coming from countries with malaria, says Prof Rogers.
Monitoring has to be greatest when the aircraft is coming from a country where malaria is endemic, especially if it is during the time of year in that nation when the disease is the biggest threat. "There will always be some places in Africa which are seasonally bad for malaria," he says. Precautions are particularly important, Prof Rogers says, in countries such as the UAE where aircraft movements are becoming more common every year as the Gulf becomes a hub for global air travel.
"In the Gulf states, it's a little bit too dry, although if you have fresh water there's a risk," he says. "It's a risk I wouldn't panic over, but it does need to be monitored by the authorities." The authorities around the world also have to be careful about many diseases other than malaria, such as dengue fever, which is spread by the Asian tiger mosquito, so named because of its striped body. They can also spread several types of encephalitis.
Unlike malaria, dengue fever can be spread by animals, making it more difficult to eliminate once it gets established. "You cannot catch and control it with good medical care like you can a human disease," Prof Rogers says. In countries including New Zealand and Australia, there is stringent monitoring of imported produce to ensure Asian tiger mosquitoes are not hitching a ride. "When a ship goes into port, they also apparently look for mosquitoes and if they see them, they will spray the ship, but I cannot believe it's 100 per cent," Prof Rogers says.
Used vehicles, fishing boats and yachts are also potential sources of alien mosquitoes. The authorities in New Zealand admit that the Asian tiger mosquito could spread through several areas of the country if it became established. Kiwis are asked by their country's Ministry of Agriculture and Fisheries to report cases of "unusual mosquito activity", such as aggressive daytime biting. So far, only one Asian tiger mosquito has been found in New Zealand, and that was a male. Males are incapable of transmitting disease. Nonetheless, the risk remains in New Zealand and Australia.
"The Australians certainly have found the Asian tiger mosquito in arriving ships, but at present this species doesn't occur in Australia, even though it is climatically suitable," Prof Rogers says. "It's knocking on the door but the quarantine authorities claim credit for its not being introduced." firstname.lastname@example.org