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Groups Mount Renewed Attack Against Malaria

Hillary Mayell
for National Geographic News
February 8, 2002
 
After several decades of moldering inattention, malaria is moving into the spotlight as cases reach epidemic proportions amid growing resistance to the drugs and insecticides used to combat the disease.

In the first hard look at epidemiological data in 50 years, researchers say the number of deaths from malaria has been seriously underestimated.




For the past 50 years, it's been widely cited that malaria causes one million deaths a year—one person dies from the disease every 30 seconds. But the Multilateral Initiative on Malaria (MIM) recently found that the number of annual malaria-related deaths could be as high as 2.7 million. Most of the victims are children under the age of five.

"Malaria is a global disease," said Regina Rabinovich, director of the Malaria Vaccine Initiative (MVI). "It affects 40 percent of the global population, and it's killing children. It's a disease worth preventing, and if we can't do it with a vaccine, we need to do it with the tools we have at hand, which is a combination of bed nets, insecticide spraying, and mosquito control strategies."

Malaria received a great deal of attention several decades ago, and during the 1930s to the 1950s it was essentially eliminated in most temperate regions of the world. But in sub-tropical regions, where the Anopheles mosquito is never killed off by the cold, the infection rate has steadily risen.

Factors contributing to the soaring infection rate include increased irrigation for agriculture, dam building, deforestation, rapidly growing populations in regions of high malaria transmission, and weakened public health care systems.

The determination to tackle the disease has steadily gained momentum in recent years as international agencies, non-governmental agencies, pharmaceutical companies, and research scientists have formed collaborative anti-malaria efforts.

A "Roll Back Malaria" campaign sponsored by the World Health Organization (WHO) is urging governments to devote more funding to malaria prevention and treatment, with the aim of cutting the burden of the disease in half by 2010. MIM was formed in 1997 to coordinate research and work with African scientists; many of the main funding agencies work through MIM. The Malaria Vaccine Initiative, supported by the Bill and Melinda Gates Foundation, was established in 1999 to spearhead the search for a vaccine.

"There is a pragmatic malaria control strategy to reduce the burden of disease using tools available," said Gerald T. Keusch, associate director for International Research at the National Institutes of Health and director of the MIM program.

"Those tools include case detection, effective drug treatment, and attempts to reduce exposure where possible," said Keusch. "But some of the hurdles that must be overcome are huge."

High Social, Economic Costs

The problem of malaria has raised greater concern in recent years because of increased awareness of the social and economic impacts of the disease. Malaria is not an "equal opportunity disease." It strikes hardest in the poorest countries of the world; 90 percent of all cases today occur in sub-Saharan Africa.

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 security—a 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 mosquitoes—having 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 suffering—you can't do that," said Keusch.

Vector control—killing the mosquitoes before they hatch—is another key tool to reducing transmission rates. Satellite technology is being employed to help predict outbreaks and locate breeding grounds to direct spraying operations.

Toward Vaccines

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 development—but 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-evasive—if 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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