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Long-lasting transition toward sustainable elimination of desert malaria under irrigation development

Significance It is recognized that the risk of malaria in dry areas is increased in the proximity of irrigation infrastructure. Although historical evidence shows that eventually malaria risks subside on the road to greater prosperity and food security, how this comes about remains poorly understood. We studied changes in land use and malaria risk in a large irrigation project in a semidesert region in northwest India. The transition phase we describe, characterized by elevated malaria despite raised control efforts, has already lasted for over a decade. The protracted nature of this transition highlights the need for a long-term commitment by health authorities and international agencies supporting irrigation schemes, to monitor health impacts and sustain control measures. In arid areas, people living in the proximity of irrigation infrastructure are potentially exposed to a higher risk of malaria due to changes in ecohydrological conditions that lead to increased vector abundance. However, irrigation provides a pathway to economic prosperity that over longer time scales is expected to counteract these negative effects. A better understanding of this transition between increased malaria risk and regional elimination, in particular whether it is slow or abrupt, is relevant to sustainable development and disease management. By relying on space as a surrogate for stages of time, we investigate this transition in a semidesert region of India where a megairrigation project is underway and expected to cover more than 1,900 million hectares and benefit around 1 million farmers. Based on spatio-temporal epidemiological cases of Plasmodium vivax malaria and land-use irrigation from remote sensing sources, we show that this transition is characterized by an enhanced risk in areas adjacent to the trunk of the irrigation network, despite a forceful and costly insecticide-based control. Moreover, this transition between climate-driven epidemics and sustained low risk has already lasted a decade. Given the magnitude of these projects, these results suggest that increased health costs have to be planned for over a long time horizon. They further highlight the need to integrate assessments of both health and environmental impacts to guide adaptive mitigation strategies. Our results should help to define and track these transitions in other arid parts of the world subjected to similar tradeoffs.