JOHANNESBURG: Over one million people in sub-Saharan Africa contract malaria annually because they live near a large dam - a number which is over four times greater than previously estimated, according to a new study.
The study has for the first time correlated the location of large dams with the incidence of malaria and quantified impacts across the region.
Researchers found that construction of an expected 78 major new dams in sub-Saharan Africa over the next few years will lead to an additional 56,000 malaria cases annually.
Encouraged by the increased volume of international aid for water resource development, sub-Saharan Africa has, in recent years, experienced a new era of large dam construction.
"Dams are at the centre of much development planning in Africa. While dams clearly bring many benefits - contributing to economic growth, poverty alleviation and food security - adverse malaria impacts need to be addressed or they will undermine the sustainability of Africa's drive for development," said biologist Solomon Kibret of the University of New England in Australia, the paper's lead author.
Undertaken as part of the CGIAR Research Programme on Water, Land and Ecosystems, the study looked at 1,268 dams in sub-Saharan Africa. Of these, just under two-thirds, or 723, are in malarious areas.
The researchers compared detailed maps of malaria incidence with the dam sites.
The number of annual malaria cases associated with the dams was estimated by comparing the difference in the number of cases for communities less than five kilometres from the dam reservoir with those for communities further away.
The researchers found that a total of 15 million people live within five kilometres of dam reservoirs and are at risk, and at least 1.1 million malaria cases annually are linked to the presence of the dams.
In total, there are an estimated 174 million cases of malaria in sub-Saharan Africa per year, researchers said.
"Our study showed that the population at risk of malaria around dams is at least four times greater than previously estimated," said Kibret, noting that the authors were conservative in all their analyses.
The risk is particularly high in areas of sub-Saharan Africa with "unstable" malaria transmission, where malaria is seasonal.
The study indicated that the impact of dams on malaria in unstable areas could either lead to intensified malaria transmission or change the nature of transmission from seasonal to perennial.
The study was published in the Malaria Journal.