Besides the high number of deaths, about 500 million people contract the disease every year, triggering a vicious cycle that pushes them deeper and deeper into abject poverty. Sick people don't go to work; sick children don't go to school; parents with sick children miss days of work.
Children under the age of five living in high transmission regions become chronic victims of malaria, suffering an average of six bouts a year. High fever and febrile convulsions in infants and children can retard brain development, leading to lifelong impairment of basic mental skills.
Because malaria kills so many children under the age of five, families in vulnerable regions tend to have higher fertility rates to ensure their legacy and future securitya situation that reduces access to food, education, and health care for individual children.
Writing in the February 7 issue of the journal Nature, Harvard professor Jeffrey Sachs calls the economic and demographic toll of malaria dramatic and suggests there is a cause-and-effect connection between malaria and poverty.
Growth of income per capita from 1965 to 1990 for countries where malaria transmission is severe was only 0.4 percent per year. In comparison, economic growth for countries with much lower rates of infection was 2.3 percent per year, or more than five times higher.
Tools of Prevention
Malaria is a parasitic infection transmitted through the bite of the Anopheles mosquito. Infection rates can be reduced dramatically through the use of bed nets treated with insecticides such as pyrethroids. (Derived from pyrethrum, a naturally occurring substance in chrysanthemums, pyrethroids remain effective for six to 12 months.) But bed nets restrict movements and cut down on air circulation, so they are not always used despite their effectiveness.
"People think about the really annoying aspects of mosquitoeshaving them buzz around your ears, where you can hear them and see them," said Keusch. "But the Anopheles mosquito, which is responsible for the majority of malaria infections, is actually one of the quieter of the species, and tends to bite people on their feet.
"To get people to realize that just because they don't hear the mosquitoes doesn't mean they don't have to use their [insecticide-treated] nets is a huge hurdle," he said.
Spraying the walls of a home with DDT also dramatically reduces infection rates, but the substance has come under fire from environmental groups.
"Green groups are against the use of DDT and want a total ban on its use," said Keusch. "But from a medical point of view, there's nothing better, safer, or cheaper than indoor spraying. It's highly effective and the toxic effects on the human population and the environment are minimal and far outweighed by the benefits of reduced infection."
For one thing, Keusch noted, malaria frequently leads to severe anemia among children, which requires blood transfusions. Yet the majority of the blood available in sub-Saharan Africa is tainted with HIV, hepatitis C, and other blood-borne diseases.
"I think most medical people feel it's fine to ban DDT for agricultural use, but a total ban when there are so many people sufferingyou can't do that," said Keusch.
Vector controlkilling the mosquitoes before they hatchis another key tool to reducing transmission rates. Satellite technology is being employed to help predict outbreaks and locate breeding grounds to direct spraying operations.
Right now there is no vaccine to protect against malaria, and while anti-malarial drugs are available, the parasite that causes malaria has consistently developed resistance to such drugs. Therefore, a great deal of effort is focused on developing new drugs.
"There's not a lot of profitability for the pharmaceutical companies in developing anti-malarial drugs, which is why public-private partnerships have been developed," says Keusch. "The goal is to develop a new anti-malarial drug every five years to combat drug resistance, with the hope that an effective vaccine will be available within the next 10 to 15 years."
The Gates-supported Malaria Vaccine Initiative is currently supporting eight different projects on vaccine developmentbut it's not an easy task.
There are four species of parasites that cause malaria among humans: Plasmodium falciparum, malariae, ovale, and vivax.
"It's a very smart parasite," said Rabinovich. "Both falciparum and vivax are what we call immuno-evasiveif you attack it in one way they have ways of going around the natural barriers. Our focus right now is on a vaccine for falciparum because it's the one that is most deadly to children, causes the most severe malaria and anemia."
A vaccine for children developed in partnership with GlaxoSmithKline is currently in clinical trials in Gambia. The vaccine, RTS,S/AS02, showed a 70 percent efficacy rate in protecting adults in Gambia against infection over a short period of time.
Several other candidate vaccines are expected to move into clinical trials over the next two years. "Each project has a different timeline, but we're a good solid ten years away from having a vaccine, and then depending on whether we have to do combination tests for vivax and falciparum, it's even more time," said Rabinovich.
Even if a vaccine is developed and anti-malarial drugs maintain their effectiveness, not all the problems are amenable to technological fixes.
"In a lot of these countries, there's no regulatory process at all," said Keusch. "People go to the market to buy drugs to treat a fever, and in many instances the drugs are counterfeit and have no therapeutic value at all.
Another problem, he noted, is that governments impose taxes on insecticide-treated bed nets that are sold from one country to another. "People can't afford them to begin with, and the taxes make them even more expensive," he said.
Keusch said MIM's focus is "to get the money on the ground, to train African health care workers, and to target research in Africa by Africans. That's the only way some of these barriers will be reduced."
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