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Here's how it happens, as the scientists explain it: Mosquitoes make their way on to planes in tropical regions, and at the end of a flight can escape into the increasingly warmer climates of developed countries, where they now have a better chance of surviving and proliferating.
"The real problem with malaria is that it is not rare," said study author Dr James H. Diaz, program director of environmental and occupational health at Louisiana State University in New Orleans. "It's the most common cause of infections in the world. It kills over 12 million people per year, and they're probably 300 to 500 million cases in the world every year. And the malaria-endemic areas of the world are themselves growing as the world warms."
Anywhere in 24 hours
"And we also know that an infected patient can get on a plane and get anywhere in 24 hours," added Diaz. "And an infected mosquito can get on a plane, as well. And in a warming world where mosquitoes live longer, have more breeding areas, and longer egg-laying seasons, this is a why the disease can be reintroduced into areas where it is now uncommon, such as the US"
Diaz and his colleagues presented their findings Monday at the American Society of Tropical Medicine and Hygiene annual meeting, in New Orleans.
Diaz explained that in the more developed areas of the world where malaria is not widespread, the most common type of malaria is "imported malaria."
As distinguished from "airport malaria," this form of disease transmission simply involves the travel of a patient who had previously been infected with the illness in a region where malaria is common to regions where the disease is not common, such as the US and Europe.
Diaz noted that the second most common means of transmitting malaria in regions where malaria is rare involves mosquitoes local to the region biting a traveller previously infected in a malaria-prone location. The mosquito then goes on to infect people living in the non-endemic region.
Least likely scenario
In the third instance, "airport malaria" is considered to be the least likely transmission scenario in malaria-free locales. In this case, a malaria-infected mosquito actually makes it way onto a plane travelling into a non-endemic zone. It then leaves the plane upon landing and bites somebody within a mile or so of the airport.
The authors point out that in 1999, the West Nile virus probably arrived in the United States by air via an infected traveller or an infected mosquito, eventually leading to the infection of local wild birds that in turn flew across the United States The result: 4 000 human infections that caused the death of 263 patients.
To highlight the serious potential for malaria to track the same route into currently non-infected regions, the researchers observe that a 1983 analysis of international planes coming from tropical regions to Gatwick Airport in London found that 12 of 67 planes were carrying mosquitoes.
To date, two cases of "airport malaria" were identified at Gatwick in 1983, and another six cases were uncovered at Charles de Gaulle Airport in Paris in 1994.
"It's very rare," admitted Diaz. "But it will happen in the US, if it hasn't happened already."
Fumigation suggested
Meanwhile, Dr Philip Tierno, director of clinical microbiology and immunology at New York University Medical Centre, suggested that plane fumigation is one potential solution to the problem.
"In an article I wrote about a year or two ago, I stressed the need to fumigate airlines as the passengers disembark, especially if they originate from areas that have endemic malaria," he said. "But airlines don't want to do it, because some people may have an adverse reaction to the fumigate, and it takes time and money, and it's not part of the current turnaround procedure. But I think it should be mandated by the World Health Organization."
Tierno said that, in the absence of such preventative steps, the threat is significant.
"I can say that airport malaria has occurred in the past and will occur in the future unless something is done about it," he said. "I don't think it would be a situation that would give rise to large numbers of individuals getting ill, judging on the past experience we have over decades of flying. But I do think it can get worse if air travel increases, which it might. So, I think the more significant thing is, you don't want any number of individuals coming down with airport malaria if you can help it."
(HealthDayNews, December 2008)
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