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Can the Mosquito Speak?
In the summer of 1942 two forces invaded Egypt, and each provoked a decisive battle. Only one of the two was human, so only that one is remembered, although the casualties in the other battle were greater. On the northwest coast, Erwin Rommel's Afrika Corps crossed the border from Libya and was halted on its march toward Cairo by the British Eighth Army at al-Alamein. Four months later the British counterattacked. After a two-week tank battle they routed the German and Italian forces, whom they outnumbered in men and tanks by more than two to one. Al-Alamein was the Allies' first decisive land victory in World War II and, along with the Soviet victory a month later at Stalingrad, appeared to turn the tide of the war. No count of the casualties was possible given the scale of violence and the disarray among the defeated forces, but somewhere between fifty and seventy thousand soldiers may have been killed, wounded, or missing. Long after the armies moved on, moreover, the battle continued to claim its victims. Al-Alamein marked the first use of land mines as a major weapon of war. It was responsible for threequarters of the twenty-three million uncleared mines Egypt accumulated in the twentieth century, the largest number of any country in the world.
Meanwhile, at the other end of the country another invader arrived, descending down the Nile valley from Sudan: the Anopheles gambiae, a mosquito native to sub-Saharan Africa but previously unknown in Egypt. The gambiae mosquito carried in its stomach the malignant form of the malaria parasite, Plasmodium falciparum. Other species of malarial mosquitoes existed in Egypt, but these carried a more benign form of malaria and were confined to small pockets in the north, where the local population had developed a degree of immunity. There were no local defenses against Plasmodium falciparum. The first reports of an outbreak of gambiae malaria came in March 1942 from the villages of Nubia, the country lying across Egypt's southern border with Sudan. The epidemic reached Aswan by July and Luxor by August, then continued north to Asyut, the largest city in the south. As at al-Alamein, the number of victims was unknown and unknowable. It was estimated that three-quarters of a million people may have contracted the disease in the three years of the epidemic, and between one and two hundred thousand died.
I first heard about the 1942 malaria invasion in 1989 from a man named Amm Ibrahim, who lived in a village near Luxor where I was spending time. Then in his eighties, he was the most informed narrator of the history of the village, and the story of the malaria epidemic was always the most vivid part of his narrative. It killed one-third of the village, he used to say, and there were not enough healthy men left alive even to carry the dead. People were hauled to their graves on the back of a camel.
The war and the epidemic interacted with a third threat to the country, a severe wartime shortage of food. The shortage had complex causes of its own. In 1933 the dam across the river Nile at Aswan, built at the turn of the century, had been increased in height, completing a network of dams, barrages, and canals begun in the mid-nineteenth century that converted most of the country's agricultural land to year-round irrigation. Only one-fifth of the Nile valley was now irrigated by the river's annual flood, which in the past had fertilized the soil by depositing a layer of silt and nutrients. The other four-fifths required chemical fertilizers. By the end of the 1930s Egyptian farmers were using 600,000 tons of fertilizer a year—mostly the new artificial nitrates—at the highest rate per cultivated area in the world. An international cartel among chemical manufacturers had assigned 80 percent of the Egyptian market to a consortium led by the German business group I. G. Farben, one of whose companies had invented the process for synthesizing ammonium nitrate. These supplies were cut off by the outbreak of war.
The lack of fertilizer caused the yield of wheat and other crops to drop by as much as a quarter. The government introduced food rationing to supply the cities and the British troops, and introduced fertilizer rationing and acreage controls to force landowners to switch half the country's cotton fields to the cultivation of food. In the far south, however, the main commercial crop was sugarcane rather than cotton, for which no controls were introduced. The owners of the cane plantations extended the crop's acreage by as much as 30 percent during the war, exacerbating the shortage of staple foods in the region hit by gambiae malaria (and increasing the breeding grounds for mosquitoes). In the second year of the malaria epidemic casualties were much higher, since many households had been too sick to harvest the previous year's food crop and were weakened by famine and malnutrition. The highest casualty rates were recorded among the workers on the sugar estates. At one of the largest cane plantations, a few miles south of Luxor, the manager estimated that malaria affected 80 to 90 percent of the people, and the doctor in the nearby town of Armant reported eighty to ninety deaths a day.
The elements combining to cause the disaster of 1942–44 represented some of the most powerful transformations of the twentieth century. First, there was the damming of the river. The building of the original barrage at Aswan in 1898–1902 helped inaugurate around the world an era of engineering on a new scale. Schemes to block the flow of large rivers were to become the century's largest construction projects. Dams were unique in the scope and manner in which they altered the distribution of resources across space and time, among entire communities and ecosystems. They offered more than just a promise of agricultural development or technical progress. For many postcolonial governments, this ability to rearrange the natural and social environment became a means to demonstrate the strength of the modern state as a techno-economic power. Second, there were the synthetic chemicals. The manufacture of artificial nitrates introduced a transformation even greater than the building of dams. From the largely synthetic-free world of 1925, the production of new chemicals, led by nitrates, grew at a phenomenal rate. In the United States output increased tenfold in each decade. By the 1980s there were four million synthetic chemicals in production, sixty thousand of which were in common use. This transformation had an impact at the level of the cell and the organism to rival that of dams at the national level. Third, there was malaria, which took advantage of irrigation schemes, population movements, and changes in agriculture to become the world's most deadly infectious disease. Plasmodium falciparum represented only 30 percent of clinical malaria cases but was responsible for up to 90 percent of the deaths. It was so widespread that no one could agree even to the nearest million how many lives it was taking each year. Finally, there was the war. Al-Alamein was remembered as the first great mechanized conflict, in which the German panzers, used in new kinds of tactical combination with antitank guns and aircraft, engaged the larger Grant and Sherman tanks. Yet the battle front was so narrow, and the German and Italian machinery so short of fuel and ammunition, that the two-week battle was fought at close quarters, like a battle of World War I. It epitomized a new and lethal interaction of man and machine.
Dams, blood-borne parasites, synthetic chemicals, mechanized war, and man-made famine coincided and interacted. It is not surprising to find disease brought by environmental transformation, industrial chemistry shaped by military needs, or war accompanied by famine. Nevertheless, their interaction presents a challenge. How exactly did tanks and parasites and synthetic nitrates affect one another? What kind of explanation can bring them together?
The war and the epidemic interacted on several levels. At the outbreak of hostilities Britain had reimposed martial law on Egypt, after the country had enjoyed almost two decades of partial independence from the colonial occupation established in 1882. The authorities censored reporting of the malaria epidemic, hoping to contain it in the south. Already preparing to evacuate Cairo in case Rommel broke through at al-Alamein, the British were unwilling to divert men and resources from the north to meet the invader from the south. This helped the gambiae mosquito advance. The British also faced a shortage of quinine, the only treatment against the infection, for in the same month that gambiae malaria was reported in Nubia the Japanese had occupied Java, cutting off the Dutch cinchona plantations whose trees supplied the drug to Europe. So the Egyptian Ministry of Health was left to launch its own antimalaria campaign. Its eradication teams attacked the disease vector—the mosquito—rather than the parasite itself, spreading Malariol, diesel oil mixed with a spreading agent, on pools of standing water. The oil formed a film on the water surface, which prevented the mosquito larvae from hatching. Malariol tended to go missing, however, since irrigation pumps could use the diesel oil as fuel, which the war had made it difficult to obtain. The eradication teams later replaced it with Paris green, a mixture of arsenic powder and copper acetate used originally as a painters' pigment, which proved a more reliable larvicide, or at least one less liable to be taken over for other purposes.
The war may even have brought the epidemic. The anopheles mosquito has a range of only two miles, so to reach Egypt it needed vectors of its own. One view was that it must have arrived by airplane, a mode of travel not unusual for mosquitoes. German air and submarine attacks had made the Mediterranean unsafe, so the British were flying a new supply route to Cairo via West Africa and Sudan. But the hostilities may also have enabled the mosquito to reach Egypt by boat. The war had increased river traffic with Sudan, and the building and raising of the Aswan Dam had created new breeding places for the insect along the route. Once in Egypt, the mosquito continued to travel north, moving by boat, train, and motorcar. To prevent its movement, these vehicles were treated by a new technique, the pyrethrum spray, developed over the previous decade to combat a major outbreak of malaria in Natal Province on the east coast of South Africa—like Upper Egypt, a region producing sugarcane. Pyrethrum powder, made of the dried flowers of the pyrethrum variety of chrysanthemum and sometimes burned to fumigate houses against insects, was mixed with green soap and glycerine and then forced through the spray nozzle of a stirrup pump, making a fine poisonous mist that killed the adult mosquitoes.
Disease often moves with the changing movements of people, and modern war causes large numbers to find routes outside existing networks of trade and migration. But having taken advantage of new kinds of transport and traffic routes, the insect also needed ways to establish itself by colonizing new territory and populations. The patterns of war and transportation had to intersect with other developments, in particular changing hydraulics. In the same years that the gambiae mosquito began to move north from equatorial Africa along the Upper Nile valley, it also crossed the Atlantic to the coast of Brazil. In both Brazil and the Upper Nile the mosquito took advantage of recent irrigation works and changed patterns of water use. In the case of the Nile, the British had extended the control of the river at Aswan by constructing further storage reservoirs in the Anglo-Egyptian-occupied Sudan. Dams were completed across the Blue Nile at Sennar, two hundred miles south of Khartoum, the Sudanese capital, in 1925, and across the White Nile at Jabal Aulia, thirty miles above Khartoum, in 1937. These projects were followed by reports of new levels of endemic disease, including schistosomiasis (a parasitic worm infection carried by an aquatic snail that would eventually affect all of Egypt, and whose treatment later introduced another endemic infection, hepatitis C, in possibly the world's largest transmission of blood-borne pathogens from medical intervention) as well as malaria. The linking together of the river control projects enabled the mosquito to jump barriers from one region to the next. The accompanying cultivation based on perennial irrigation created many breeding places among a thicker population of human hosts that often lived much closer to the water now that flooding no longer occurred in many areas. The engineers who built the irrigation works had not considered the possibility that snails or mosquitoes would make use of their work to move, or that certain parasites would travel with these hosts, or that devastating consequences would ensue. In a private report in 1942, however, the British acknowledged that the surest way to restore the health of the Egyptian population would be to destroy the dams and return to basin irrigation.
The irrigation works led to other unexpected effects. The damming of the river altered the distribution and timing of its flow, as well as the temperature and chemistry of the water. This affected the riverbed and banks, altering the character of the riverine environment. Microorganisms and plants dependent on the balance of the river's ebb and flood disappeared, while other, more aggressive species took advantage of the change. Curly pondweed, or Potamogeton crispus, one of the most invasive aquatic plants, began to form large islands of weed, which the river's current carried in clumps downstream. An Egyptian malaria expert established that the Anopheles gambiae in turn made use of the pondweed, which transported the larvae of the mosquito from one breeding area to the next.
If the gambiae mosquito benefited from the changes in the flow and chemistry of the Nile, its parasite, needing human bodies for reproduction, was also able to take advantage. As a spore-forming parasite, the plasmodium did not set out to kill its human victims, but entered their bodies merely to complete its unusual life cycle. Transferred by the bite of the female mosquito, the young spores take up residence for about a week in the cells of the victim's liver. Each spore then bursts apart and releases into the bloodstream up to forty thousand offspring, which feed off the blood's cell hemoglobin and multiply into further offspring, some of which assume separate male and female forms. The explosive reproduction is not intended to kill the victim, but to ensure that with the bite of another mosquito a number of spores are ingested back into the stomach of the insect, where they fertilize and complete the reproductive cycle. However, the malignant form of the parasite brought by the new invader to southern Egypt makes the red blood cells of its victims particularly sticky, clogging the arteries and depriving the body of oxygen. Most victims survive after a severe fever, which ensures that the parasite still has hosts in which to live. But if the brain or another vital organ is deprived of oxygen, the unwilling host can die.
In Upper Egypt the plasmodium found a population with no immune response to interrupt its infection cycle, for it was a new arrival. It also found a population whose bodies had been transformed by the sugar industry. From the 1920s Egypt's newly independent government was for the first time able to protect local manufacturing, in particular sugar production, the country's oldest and largest modern industry. Price protection against the global market in the 1930s and 1940s combined with the irrigation work supported the extension of cultivation. Perennial irrigation and cane cultivation reduced the fertility of the soil and the land available for food production. When the war interrupted the supply of artificial fertilizer, these factors combined to make the people of southern Egypt far more vulnerable to the plasmodium parasite. In contrast to the badly nourished residents of southern Egypt, none of the government officials, medical workers, or eradication teams, nor the wealthy women from Cairo who launched a charity relief operation in the south, lost their lives in the epidemic. Furthermore, reports from Brazil indicate that sugarcane juice, which those working on sugar plantations consumed on site by breaking and chewing the cane, can worsen the effects of malaria. Thus on several levels the parasite found that sugar had left the bodies it encountered less able to resist infection. The chemistry of the epidemic operated at the level of the nation and of the cell.
Excerpted from Rule of Experts by Timothy Mitchell. Copyright © 2002 the Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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