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The Making of A Tropical Disease: Malaria, Poverty and a Tale of Reverse Causality

September 14, 2011

By Fiorenzo Conte

This is the first of two posts which review the book “The Making of a Tropical Disease: A Short History of Malaria” by professor Randall Packard and discuss its policy implications.

The current debate about malaria is dominated by an influential paper by Jeffrey Sachs and Pia Malaney who investigate the economic and social impacts of malaria. The argument put forth is that malaria drives poverty and economic stagnations as cross-country regressions show that countries located in areas with high P. falciparum transmission in 1965 experience lower rates of economic growth vis-à-vis countries with lower malaria parasite transmission. The authors conclude that malaria imposes an economic burden and that this can happen via a variety of channels (amongst others – direct medical costs, foregone income, absenteeism of school aged children due to morbidity and consequent hampered acquisition of human capital). The possibility of reverse causality – i.e. of poverty driving malaria infections – is taken into consideration but dismissed to some extent insofar as malaria incidence in African villages varies little across different income levels.

The book The Making of A Tropical Disease tells us that such overemphasis on this direction of causality is misplaced. To understand why, one needs to look at a basic yet fundamental fact: malaria occurs in those areas where environmental changes make possible the growth of anopheline mosquito, where human population exist who are susceptible to be infected and where malaria parasites are present. The convergence of the three conditions has historically happened as a result of wider societal forces. And amongst these forces, economic stagnation can account for a great deal of malaria occurrence. From this perspective is poverty which drives malaria incidence.

Consider for example the case of malaria epidemic which hit the zone of Sertao in Northeastern Brazil in 1938-1939. Patterns of land ownership and economic stratification determined how the epidemic played out. In the Sertao region few landowners had the control over land thus forcing the landless farmers who were the majority of the population to live as sharecroppers on large estates called fazenda. As the margin of profit was very limited for the sharecroppers during normal time, the occurrence of drought pushed the sharecroppers to resort to other responses. The most common was migration. When an extended drought hit the areas in 1936 thousands of those landless farmers migrated to the coast in search of employment in the sugar plantation or to the Amazon region to earn income collecting rubber. Both the coastal and the Amazon region were malaria endemic areas whereby the malaria transmission in the Sertao occurred only seasonally thus leaving the local farmers susceptible to the contraction of malaria. This little resistance to malaria compounded by malnutrition were responsible for the ravages that malaria made amongst the refugee- migrants from the Sertao. To make matters worse, as migrants moved back to the Sertao they brought with them the parasites thus setting the stage for a major outbreak of malaria in the region. In sum, the poverty and condition of landlessness of the sharecroppers in the Sertao determined their migration thus increasing their exposure to malaria infections. Poverty drove the malaria outbreak.

The story of Northeastern Brazil tells us another thing: not only poverty creates the conditions for a malaria outbreak but it also determine – contrary to what Sachs and colleagues argue – who the most affected people are. This point is corroborated by  history of 1930s malaria outbreaks in South Africa. Africans who had traditionally lived in the highland plateau of Transvaal were evicted as white settlers moved into the region and took control of the land. To avoid the condition of sharecroppers, they moved to the lowland coastal plains which had been designated for African settlements. The Africans who moved faced a high risk of malaria insofar as they had little immunity to the disease and they found themselves in a malaria endemic area such as the lowland. The disease however affected also poor white settlers in the lowland who had poor housing conditions, did not have the means to invest in screening or to use quinine. Hence, class and level of income determined the victims of the infections.

The next post will discuss the implications of this lesson when it comes to evaluating policy which seeks to fight malaria and what are the policy conclusions that should be drawn. Stay tuned!!!

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