Picture a place where children are so infested with parasites that they are listless and weak. Even when they are feeling well enough to go to school, they are so anemic that learning is difficult. While this could be a scene in many of today's poor, tropical countries, it was also typical in the southern United States less than a century ago. In 1910 about 40 percent of Southern children suffered from infection by hookworm, a tiny bloodsucking worm that invaded their intestines. Malaria also infected a large fraction of Southerners back then.
In fact, hookworm and malaria were so prevalent in the South that historians blame them for giving rise to the widespread stereotype of the “lazy Southerner.” Yet they were so successfully and thoroughly vanquished, that the notion of hookworm and malaria in the southern United States sounds improbable today.
The experience of the U.S. South shows that disease environments, even those that are so persistent and prevalent that they become part of the fabric of daily life, can be changed for the better. Furthermore, in my research, I find that doing so can lead to large economic payoffs down the road.
How do we know that it was the elimination of disease that led to higher economic growth and not the other way around? After all, higher incomes tend to go hand in hand with better living conditions and public health systems. In the case of the American South, it was “big push” campaigns propelled by advances in medical knowledge and by money from philanthropists like John D. Rockefeller—both of which came from outside the afflicted regions—which began to eradicate these diseases.
The eradication campaigns provided results that were immediate and sometimes dramatic. On the effects of deworming, a fairly typical letter from from Virginia reported that “children who were listless and dull are now active and alert; children who could not study a year ago are not only studying now, but are finding joy in learning,” and a superintendent in Louisiana wrote that “in short, we have here in our school-rooms today about 120 bright, rosy-faced children, whereas had you not been sent here to treat them we would have had that many pale-faced, stupid children.”
But the real big economic payoff would be apparent several decades later, when the children who grew up without having their physical and cognitive development dragged down by disease entered the labor force. In my research, I find that the generations born after the disease eradication campaigns in the American South had higher incomes and levels of literacy as adults than the preceding generations—beyond what you would expect from the existing trends in economic growth. Moreover, the jump in income from one generation to the next was significantly greater in the areas that had been most afflicted by tropical disease prior to the public health campaigns. According to my calculations, these two diseases depressed economic development so much that each could account for roughly 15% of the income difference between the wealthier North and the impoverished South in 1900.
And, the large benefits of eradicating these diseases are not unique to this once-poor region in a rich country. In my research, I also examined the DDT-based campaigns against malaria in Brazil, Colombia, and Mexico at mid-20th-century. Given the much larger infection rates in these countries relative to the turn-of-the-century southern United States, the total economic benefits of eradication were even greater, and malaria accounted for at least 12% of income gap between the US and Latin America. Yet, the results were remarkably similar in magnitude, per unit malaria, to the estimates from the Southern US. Similarly, Adrienne Lucas of Wellesley found positive impacts on education from anti-malaria campaigns in Paraguay and Sri Lanka. And, a deworming program in Kenya was found to cut school absenteeism by 25 percent, according to research by Edward Miguel and Michael Kremer, of UC-Berkeley and Harvard respectively, a number remarkably similar to my estimates from the Southern US.
Are hookworm and malaria unusual diseases? Not in the sense that over two billion people worldwide are infected with these and related parasites. But, yes, in the sense that these parasites cause a relatively high burden of morbidity, especially among children who are in the critical stages of physical and cognitive development, depriving them of their full human potential. These features make for a sharp contrast with diseases that have high case-fatality rates and/or short-lived bouts of morbidity, such as smallpox. Whatever effects eradicating smallpox had, they probably worked through changes in mortality rates, and the consequences were therefore very different from the effects of eradicating tropical parasites. I do not argue (nor do I believe) that the eradication of any conceivable disease would necessarily have such large effects as those seen for hookworm and malaria. To understand the relationship between health and development, we cannot think of health as an undifferentiated mass.
But is controlling tropical disease feasible? Consider the case of hookworm eradication in the American South. Deworming treatments are short-term solutions, and follow-up efforts by private and governmental actors played a key role in consolidating the gains from Rockefeller's campaign. Harder to measure, but important, hookworm entered into the public consciousness. Growing up in the South myself, I remember older relatives' teasing me by asking if my toes itched. By that time, such comments were more joke than menace, but they stemmed from a profound impression left years earlier. An interesting comparison comes from Puerto Rico. Around the time of the Rockefeller campaign, a commission from the US Army sponsored anti-hookworm efforts throughout Puerto Rico. Large gains against hookworm were realized during the campaign, but the colonial government provided little follow-up, and these gains mostly disappeared a decade later. Moreover, recent work in Kenya by Kremer and Miguel suggests that the initial impulse provided by short-term injections of medication and publicity may have little long-term effect on behavior. Similar issues arise with malaria. The US achieved eradication of malaria in the South and in the Panama Canal Zone. But eradication from much of the rural, tropical world has proved elusive. A common criticism of the DDT-based campaigns is that governments did not sustain high levels of support after malaria had initially declined, which allowed the resurgence of DDT-resistant mosquitoes.
Improving tropical health is a long, hard slog, and interventionistas should be ready for as much. But the rewards for controlling these diseases can be tremendous, in both humanitarian and economic terms.
