The Monster Mosquito

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MEDICINE AUGUST 12, 2010

The Monster Mosquito

The Fever: How Malaria Has Ruled Humankind for 500,000 Years
by Sonia Shah
Sarah Crichton Books, 320 pp., $26

In the fourteenth century the Black Death killed a quarter of Europe and Asia in three years. The influenza pandemic in 1918 killed fifty million people worldwide. But in its stealthy, creeping, horrible way, malaria—which predates Homo sapiens—is probably the greatest predator humanity has ever known. Malaria is a specialist: almost all walking, crawling, or winged animal has its own specific malarial parasites. Humanity has no less than four of them, and a fifth seems to be evolving. You would expect this ancient history to be echoed in our genome, and it is: one in fourteen human beings has some genetic trait involving malaria resistance. That perhaps a half-dozen separate genetic resistance traits—some of them quite unpleasant for their carriers—exist in human populations testifies to malaria's tracks across our past.

Despite this long war, the parasites are as deadly as ever. Some germs, such as influenza, rely on mobile hosts—people who are well enough to walk around and cough and sneeze and thus spread their germs. Others, like malaria, rely on vectors—Anopheles mosquitoes, in this case. A mosquito flying through an open window can bite someone stricken by severe illness and then spread virulent germs to someone else. Malaria remains deadly because there is often no way to keep mosquitoes away from people who are gravely ill. Every year—despite new drugs, constant research, and hundreds of volunteers distributing insecticide-impregnated mosquito nets—nearly one million people die from the disease.

If you are looking for a real biological understanding of how malaria works, Sonia Shah’s new book is not for you. Still, her book remains the closest thing we have to a popular anthropology of malaria. Shah illustrates the terrible double-edged blade of acquired immunity and the dilemma this creates for the army of earnest researchers, experts, and activists who want to stop the carnage, perhaps for all time. The problem is that repeated malaria infection protects more people than it kills. The American-born Shah charmingly describes her own childhood visits to India, where she would wake each morning stippled by the red, mounded depredations of mosquitoes. Her cousins, sleeping free on open pallets, would show smooth, unmarked skin. And when she recently told her Indian relatives she was writing a book on malaria, they were puzzled. To them, malaria is not something to fuss about.

Children who contract falciparum malaria—the deadliest form—early in life develop considerable immunity to the disease. You might have a new infection several times a year and feel poorly, but the next day you will wake up healthy. But as Shah explains, if bed nets, drugs, and insecticidal sprays beat the germs and keep the mosquitoes away from your village for a year or two, and then you get bitten by a wandering malarial mosquito, you might get very sick, or die. Moreover, when you subject germs to drugs that kill them, a funny thing happens: natural selection will favor those germs that survive. Soon you have an entire population of resistant germs, and the drug is useless. Similarly, insecticide-laced bed nets or DDT sprayed on walls will eventually produce resistant mosquitoes.   

In other words, malaria has got to be eradicated, once and for all, or the double-edged blade remains poised to strike. This is where Shah's contribution is strongest: she takes the reader through a fascinating history of the attempts to eradicate, locally and globally, this troublesome scourge. The social injustice of early eradication efforts also angers Shah. Attempts to banish the disease and its vectors locally often benefited only whites. In colonial India, the British “knowingly worsened malaria” by building irrigation systems that ran against normal land drainage patterns. This promoted an onslaught of mosquitoes and malaria—but only among the natives; the British overlords themselves lived in dry, cool hill towns behind windows. In Panama, it was much the same story: white workers lived in well-drained areas, but black workers were told to live in the bush to “protect them from pneumonia.” Blacks had a “special biology” that protected them from malaria, doctors thought—but many of these black workers came from malaria-free Barbados, and had no acquired immunity whatsoever.    

Shah's indignation is often justified, but sometimes her rage substitutes for reason. The lavishly appointed headquarters of the Harvard Malaria Initiative incurs her scorn because it “conveys a single, resounding message: this is where very important, very well-funded activities occur.” The lead investigator wants to explore malaria's basic biology to identify specific genetic targets and produce novel, specific drug interventions. This approach might work, or it might not. But Shah declares that focused, specific targets will only cause resistance, and that it is better to send investigators tromping through fields and jungles to collect traditional medicines like the very effective quinine from cinchona bark, or artemisinin, which Chinese doctors have used to treat malaria for centuries. Shah seems offended by the Harvard team's conventional medical-research approach, but there is no reason to think that holistic treatments are necessarily better than high-tech ones.      

We may not be able to eradicate malaria for all the complex reasons Shah lays out. She is insightful, even revelatory, on the problems of bed nets (they are too hot, you can tear them or toss them off, and many Africans divert them for use as fishing nets). But, though she refers to the need for “secure housing,” she barely mentions the passive barriers that actually work. Indeed, malaria and yellow fever were wiped out in the American South because screening to repel mosquitoes worked so well. Bed nets screen only those who use them properly. And air-conditioning adds another layer of protection. Though Shah concludes her book by ominously noting that the “warm blood” of industrial Westerners “beckons,” the truth is that we are quite secure behind our housing infrastructure. Malaria cannot get a foothold because it cannot reach enough fresh hosts to maintain itself.     

It is tempting to think that we could put screens on every house, every hut, and every shack across the world: malaria would not be wiped out, but it would be much less devastating, and, since mosquitoes would not have access to the gravely ill, milder strains of malaria might prevail. But in order to give secure housing to the world, we would have to wipe out poverty. Unfortunately, that quest is even more unlikely to succeed than the quest to defeat malaria. 

Wendy Orent is the author of Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease.

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