Malaria, once thought to be almost eradicated, is on the rise again, and a new map shows just how far and how fast it's spreading. Rose Hoban reports.
Decades ago, scientists and doctors thought they were about to conquer malaria. They discovered drugs against the ancient scourge. That — combined with spraying to kill the mosquitoes that transmit the parasite — managed to reduce malaria rates in many parts of the world.
And then, research on the disease came almost to a halt, according to David Smith, an infectious disease professor at the University of Florida. "There was a time starting sometime during the 70s," he says, "when the level of activity in malaria research and malaria control reached a low that lasted for several decades until people started to notice again, what a horrible toll falciparum malaria has on the world."
While scientists and governments weren't paying attention, the malaria parasite became resistant to drugs. At the same time, spraying campaigns were phased out due to cost and environmental concerns.
Rates of infection began to increase.
The 1970s is when the last global map detailing malaria prevalence was created. Now Smith and colleagues from the Wellcome Trust in England have created a new malaria map that's available on the Internet. Using simple colors and points to mark where the data come from, the map details where many people have malaria.
The map uses darker colors to note where the disease spreads most frequently — a measure called transmission intensity.
Smith says the area that has the most high, uniformly high transmission intensity is tropical Africa. "But," he points out, "there are stable areas of transmission intensity in the Amazon basin, in coastal South America stretching from Ecuador, north, some areas in Central America, and some areas of the island of Hispaniola, and then throughout India, Southeast Asia, Indonesia, Papua New Guinea, Madagascar, Sri Lanka." He concludes, "It's basically between the tropics, and all of the areas that are wet, and reasonably poor, have got it."
Smith says he and his colleagues spent three years examining more than 5000 studies, and plotting the data on the map. Much of that data came from clinic counts of patients with malaria. Smith says, surprisingly, they found the risk for transmitting the disease was not as high as many had suspected; there were not that many places in the world with an infection rate of 50 percent or more, as is the case in much of Africa.
"Broadly speaking, the rule outside of Africa was that most places that have malaria… there's less than 10% of the population that's infected," Smith says. "This is a lower risk of transmission than most people would have guessed. They wouldn't have guessed that it was commonly that low outside of Africa."
Smith says there are plans to keep this new map updated. He says maps like these are an important tool in helping target malaria hotspots and directing resources to those places where the disease poses the most risk.
The map and a companion article are published in the online journal PLoS Medicine.