Malaria: Resurgence of a Deadly Disease

Malaria kills roughly twice as many people worldwide as AIDS, drugs no longer work against some strains, and mosquitoes in diverse parts of the United States now carry the disease.

I learned another reason that mosquito nets are unlikely to solve Africa's malaria problem from Jean-François Trape, a French physician and malaria expert on the staff of the Laboratoire de Paludologie, in Dakar. Since the early nineties Trape has studied malaria transmission in two Senegalese villages, each about four hours' drive from Dakar. One of the villages, Dielmo, has a stream running through it, where Anopheles mosquitoes breed year-round. Malaria there is rampant, and children are never without parasites in their blood. The other village, Ndiop, has high malaria transmission only during the rainy season, which lasts about four months. Dielmo residents, exposed to an average of 200 infectious mosquito bites a year, experience an average of forty-three attacks of malaria from birth to age sixty. Ndiop residents, who get roughly ten infectious bites a year, average sixty-two malaria attacks. Trape explains this apparent paradox by pointing out that the villagers of Dielmo are more likely to have the bulk of their attacks during childhood, thereby boosting their resistance to the disease. Their bodies come to an uneasy truce with malaria, in which constant infection weakens but does not kill them. Trape argues that providing people with bed nets to ward off malaria in areas where it is highly endemic may in fact increase their risk of dying from the disease, by reducing but not eliminating their exposure. The gambiae mosquito can transmit the malaria parasite in a single bite. If the transmission rate is reduced to fewer than two attacks a year, a person may lose his or her partial resistance to the disease between bouts. Therefore, Trape told me, in areas where malaria transmission is reduced but not eliminated, adults get sicker and older children die at only a slightly later age than do their counterparts where the rate of transmission is higher. "I have two children, and I can tell you, as they get older, you invest in them more," Trape said. "In African culture people prepare for the death of an infant but not a ten-year-old. The nets in many cases simply delay the inevitable."

THIÈS is Senegal's second largest city, after Dakar, but by Western standards it's a village with sprawl. The center is small enough to cover on foot in about an hour, and most of the traffic is human. Goats and chickens poke through the streets, and children stare and wave. Diawara takes me to the Service de Lutte Anti-Parasitaire, which he directs. It is housed in a barrackslike brick structure surrounding an open courtyard where women sit, fanning flies away from buckets of fish. These are technicians' wives, who live here with their children while their husbands do fieldwork. Although Diawara has a wife and four sons in Dakar, he spends most weeknights here, sleeping on a bench in his office. The office is equipped with a computer that collapses from heat exhaustion each summer. A broken air-conditioner lurks near the ceiling. There are no screens on the doors or glass in the windows, but there is a giant-sized can of bug spray. On the wall is a map of Senegal, bristling with straight pins. The pins designate areas where mosquitoes have been trapped, dissected, and examined for parasites. From the dates on the pins I learn that Senegal has been trapping and dissecting mosquitoes for about thirty-five years. Given that most of the country is swarming with parasite-carrying insects, the point of this exercise eludes me.

Diawara introduces me to his head technician, a small, neatly made man of about sixty in a stained lab coat, who bows and pulls out tray after tray of mosquitoes. The mosquitoes were snared by the men I noticed lounging in the shade in the village we visited that morning. The men are paid three dollars a session to sit with their pants legs rolled up. Their exposed legs and feet are mosquito bait (malarious mosquitoes have a preference for the lower extremities). When a mosquito alights, the man traps it in a small glass vial. In the rainy season, when transmission is fiercest, a man can trap as many as 300 mosquitoes in an eight-hour shift. Up to one percent of these carry the falciparum parasite in their salivary glands.

Diawara sweeps a plastic cover from a microscope, slips in a slide, and focuses expertly to show me falciparum in action. What appears under the microscope at this moment looks relatively benign: the malaria parasite is stained a cheery red against the dimmer red of the infected cell. But I have seen greatly enlarged photographs of malaria parasites pouring from the ghostly white hulks of dead blood cells, like soldiers fleeing a scorched-earth spree, and the sight is frightening. Fierce and sometimes fatal anemia is only one consequence of such an attack. The parasite can alter human blood cells so that they adhere to blood vessels; in the case of cerebral malaria the infected cells can occlude capillaries to the brain.

I saw children with cerebral malaria in clinics near Dakar. In one clinic I visited, every child admitted was being treated for it. The head physician there, Mouhaumadou Fall, who is also the chief of pediatrics at the University of Dakar's medical school, explained that it was "pediatric strategy to always treat for malaria, even without proof." The children with full-blown cerebral malaria looked terrible. Their eyes were unfocused under half-closed lids, and they lay absolutely still. Scientists aren't sure, but they believe that cerebral malaria causes brain damage in about 10 percent of cases, and it is estimated that another 10 to 50 percent of cases result in death. But the disease is treatable if caught early enough. One fifteen-month-old at the clinic who just days before had undergone treatment was so lively that his mother joked about stuffing him into her pocket for safekeeping.

For complex reasons, women who have acquired partial resistance to malaria lose it during their first pregnancy, and tend to get very ill with the disease. They are more likely than the uninfected to die in childbirth, and there's about a 40 percent chance that the baby will have a low birth weight. Malaria can damage the brain and other vital organs, and cause heart failure, respiratory distress, kidney failure, bleeding disorders, and any number of other systemic breakdowns. A study recently conducted in Gambia suggests that almost any estimate of malaria deaths woefully understates the impact of the disease, because the control of malaria seems to bring about a radical reduction in mortality from all causes. The implication is that infection with the parasite greatly increases susceptibility to other infections and to malnutrition. Some scientists have gone so far as to cite malaria as a contributor in half of all childhood deaths in Africa.

Mamadou Kasse, the medical editor of Senegal's largest newspaper, Le Soleil, told me that Africans assume that the West considers malaria a necessary evil. "Malaria keeps Africa down, and down is where the rest of the world wants us to be," he said. "If this was a disease of the West, it would be gone." Kasse is not alone in his belief. Several Western scientists told me matter-of-factly that population control, not disease control, is USAID's central mission in Africa. As one scientist told me in a confidential tone, "I'd rather die of malaria than of starvation."

Indeed, many Westerners assume that infectious diseases like malaria, tuberculosis, and AIDS are simply the price that the Third World must pay for its population problem. But Jonathan Mayer, a medical geographer at the University of Washington, argues that just the opposite is true -- that in effect poor health exacerbates overpopulation. "It's fundamental in demographic transition theory that higher death rates lead to higher birth rates," he says. "Lots of kids die of malaria before age five, which means that people will have lots more kids to make sure some stay alive. As an economy becomes more developed, improved public-health measures do lead to a temporary increase in population: at first the birth rate stays stable and the death rate goes down. But in as little as twenty years the birth rate goes down as well. That's what happened in the United States and Europe during the latter part of the nineteenth century. We got rid of malaria here, and a whole lot of other infectious diseases, but we don't suffer from overpopulation."


IT is unclear how long malaria parasites have infected human beings, but there is no doubt that the disease is an ancient scourge. Medical historians believe that it appeared with the introduction of agriculture, when the human population grew large enough to serve as a reliable reservoir for malaria parasites. The Chinese canon of medicine, the Nei Ching, which dates from about 2700 B.C., discusses the telltale symptoms of high fever and an enlarged spleen, and in their writings Aristotle, Homer, and Socrates describe cases of malaria. Hippocrates was the first to associate malaria incidence with proximity to stagnant water. The term mal'aria was coined in the sixteenth century by Italians, who insisted that the disease traveled by air. The medical microbiologist Robert Desowitz wrote in his outspoken review of infectious disease, The Malaria Capers (1991), that malaria was of particular interest to the English during Victorian times -- no surprise, given that at least a third of the hospital beds in their colonies were occupied by victims of the disease. The English carried P. vivax with them to Jamestown, and imported falciparum along with slaves from Africa. In this country malaria thrived in particular in port cities like Boston and New York, and in the South. A Scottish settler described his bouts with the disease thus: "I am now & then troubled with ye fever & ague wch. Is a very violent distemper here. . . . This place is only good for doctors & ministers." Malaria was among the most common reasons for hospitalization during the Civil War, with the two sides reporting more than 1.2 million cases between them.

Precisely a hundred years ago the British physician Ronald Ross proved that malaria is carried not by air or water but by mosquitoes -- a discovery for which Ross was awarded a Nobel Prize. The fact that mosquitoes were involved made the disease all the more frightening, because water could be purified but mosquitoes could not. Malaria was all but gone from the northern United States by the turn of the century, but it maintained a stranglehold on the South. In her forthcoming monograph "Water Won't Run Uphill: The New Deal and Malaria Control in the American South," Margaret Humphreys, a physician and medical historian at Duke University, compares the American South of the early 1900s to today's developing countries, with their colonial infrastructures, weak local governments, and pockets of extreme poverty where both health care and sanitation are minimal. Estimates vary, but there were certainly millions of cases of malaria a year in the South in the mid-1930s. In 1936 the Works Progress Administration hired 36,000 men to drain three million acres of swamp. After that initial push the WPA continued its work on a much smaller scale through 1942, when the Malaria Control in War Areas agency (the predecessor of the Centers for Disease Control) was formed. Soon thereafter the Public Health Service launched an eight-year, $50 million malaria-control program.

The program was an extension of the war effort -- the idea was to protect soldiers, and only incidentally civilians. The U.S. government had previous experience attacking malaria in the field: one of the most successful anti-disease campaigns of all time was waged in the Panama Canal Zone, where in 1904-1906 U.S. military engineers and "sanitary police" worked tirelessly to drain swamps and thereby vastly reduce the area of mosquito-breeding sites. This time the goal was to create a malaria-free zone around every military installation in the United States. American pharmacologists developed the anti-malaria drugs primaquine and chloroquine as an alternative to quinine, which at the time was being hoarded by the Japanese. Mosquitoes, officially dubbed "Public Enemy No. 1" by the Public Health Service, were pelted with insecticide bombs concocted by the Army. And DDT, itself a product of the war effort, was sprayed inside millions of American homes. (No matter that American mosquitoes seem to prefer the great outdoors.) The campaign appeared to pay off, and in 1953 America declared victory over Plasmodium.

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Ellen Ruppel Shell is the co-director of the Graduate Program in Science Journalism at Boston University. She is the author of Cheap: The High Cost of Discount Culture.

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