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The Making of A Tropical Disease 2: Policy Interventions and Omitted Variables

September 19, 2011

By Fiorenzo Conte

This is the second 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 previous post discussed the important role that a complex mix of societal forces (land ownership, patterns of agricultural development, migration, poverty) plays in shaping the occurrence of malaria epidemics. This interaction, which is called by the author the human ecology of malaria, is often ignored when it comes to evaluate policy interventions which seeks to tackle malaria by attacking the malaria vector and the malaria parasite. Yet, to omit this variable is tantamount to miss an important part of the story.

Source: Najera et al., Malaria Epidemics, Detection and Control Forecasting and Prevention, Geneva, 1998, 60

Source: Najera et al., Malaria Epidemics, Detection and Control Forecasting and Prevention, Geneva, 1998, 60

Take the example of El Salvador and its Integrated Malaria Control Program initiated in the 1980s. The major element of the campaign was an extensive network of village health workers who were trained to identify and treat any people in the community presenting fever. The success of the campaign was exceptional with number of cases dropping from 100,000 in 1980 to 4,500 in 1990. The success was mostly attributed to the commitment and flexibility of the village health workers and other elements of the program such as environmental control to eliminate breeding grounds.

If the program had its merits, there is however an omitted variable which can account for the drop in malaria cases. By 1980 most of malaria cases were occurring in the coastal region which was dominated by cotton plantation. The extensive use of pesticide for cotton production contributed to the development of pesticide resistant vectors and the use of migrant cheap labor added a reservoir of human host who had little immunity to the disease and was housed in poor conditions. In other words the expansion of sugar cane plantation led to the entrenchment of malaria in the coastal region. The cotton industry, which as at the root of the persistence of malaria, collapsed during the civil war that ravaged the country during the 1980s. As the cotton production dropped so did the malaria incidence in the area at the time of the implementation of the Integrated Malaria Control Program. If it is difficult to establish which element was more influential in driving down the malaria incidence, it is undisputable by looking at the graph above that malaria incidence closely paralleled the pattern of cotton production. The omission of this variable would have led to a totally different interpretations of events.

So, if societal factors such as migration and cotton production influence to such a great extent the pattern of malaria incidence what should we make of the current efforts to control malaria which privileges the biological causes and therefore focus on attacking anopheline mosquitoes and malaria parasites? Randal Packard has a clear idea:

If we do not address the underlying ecological force driving malaria, we will be condemned to providing protections against the disease indefinitely. For, any slackening of control will allow the forces driving malaria to rekindle the disease.

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