By establishing a link between dams and malaria, WLE-supported research has demonstrated the need to urgently integrate malaria control into water resource planning.
Dams are critically important for Africa’s water security and economic development. But they may also become hotspots for malaria transmission, posing a public health risk that threatens to undermine wider eradication efforts. Dams typically increase the presence of shallow water where mosquitos can breed, leading to enhanced malaria transmission. Changes in the placement, design and operation of dams are needed to ensure the economic benefits they generate do not come at an unacceptable cost to local communities.
Over several years, WLE-supported research has helped establish a clear link between dams and malaria transmission, underscoring the urgent need for control measures. Researchers have conservatively estimated, for instance, that large dams (at least 15 meters high with a water storage capacity of at least 3 million m3) may be responsible for approximately 1.1 million malaria cases every year.
More recently, the program investigated the risk posed by small dams (less than 15 meters in height with a water storage capacity below 3 million m3). By superimposing vector distribution data on 4,907 small dams and 258 large dams across four river basins in sub-Saharan Africa (the Limpopo, Omo-Turkana, Volta and Zambezi) researchers concluded that in each basin the cumulative risk posed by the large number of smaller dams was greater than that of existing large dams. Although the incidence of malaria per kilometer of reservoir shoreline varied between years, estimates suggest it was typically 2-7 times greater – attributed to greater population densities close to smaller dam reservoirs and conditions more conducive to mosquito breeding.
By emphasizing the malaria risk that dams pose WLE’s research has focused attention on a local condition that threatens broader progress – malaria transmission rates have declined by more than 40% in Africa this century. Crucially, the body of evidence offers important insights that are now informing control measures and demonstrating the need to integrate malaria control into water resource planning. Researchers recommend urgent changes to the placement, design and operation of dams.
Decisions on where to place dams should consider where malaria transmission is already high and how variations in topography can render some areas more susceptible than others. Planners should also reflect on climate change – not only considering implications for water storage and flooding but also thinking through how malaria threats may evolve as conditions shift over time.
Design needs to focus on effective drainage and preventing the formation of shallow pools and puddles around the reservoir shore where mosquitos can breed. Finally, water levels can also be adjusted to ensure habitats are less favorable for mosquitos. Experience in Ethiopia and elsewhere suggests that combining fluctuation and rapid drawdown can be highly effective.
Aligned with the World Health Organization (WHO) climate change and health strategy and WHO’s Health in All and One Health initiatives, insights from WLE’s research have been incorporated into a multisectoral action guide published by Partnership to End Malaria which explores options for improved coordination and collaboration and identifies the actions different sectors can adopt to prevent malaria transmission.
Increasing water storage is widely perceived as a significant contributor to climate change adaptation. This is attested by the 160 large and many more small dams that are currently being constructed across sub-Saharan Africa. The rush to develop water storage for climate change adaptation may, however, increase risks for already vulnerable people – and in some cases cancel out the benefits of greater water availability. Currently, too little thought is given to the possible public health implications of dam construction. To address this, dam builders and operators need to proactively work with public health agencies to mitigate malaria risks.
Multisectoral approaches will be critical in the years ahead – helping us to first recognize and then address the dynamic interconnections that exist between development activities and the incidence of malaria. Working across sectors offers a promising alternative to Africa’s currently fragmented approach to development, which allows the health risks posed by dams to persist despite advances made during the previous two decades.