Large dams in sub-Saharan Africa may be responsible for at least one million cases of malaria every year, according to a recent study. Journal de l’Environnement reports.
Malaria is the most widespread parasitic disease in the world. Of 198 million diagnosed cases in 2013, 90% were in sub-Saharan Africa.
New treatments have cut mortality rates by more than half since the 1990s, but malaria still killed 584,000 people in 2013 alone.
Anopheles mosquitos, the carriers of this disease, reproduce in stagnant water. Health experts fear that communities based near large bodies of fresh water, like the reservoirs made by damming rivers, could suffer from higher rates of the disease. This phenomenon has already been observed in Cameroon, Zimbabwe, Kenya and Ethiopia.
In order to better quantify the public health impact of dams, both locally and across the African continent, Solomon Kibret and a team of researchers from Australia’s University of New England collected data from 1,268 villages in sub-Saharan Africa. They compared the prevalence of malaria in communities that lived close to dams with those that lived further away.
Up to 320% more prevalent
Around 20 million Africans live within five kilometres of a dam. Almost three quarters of these people also live in areas of high risk for contracting malaria. The researchers found that the closer people live to the water, the higher their risk of contracting malaria.
In countries where the prevalence of malaria is stable, people who live less than one kilometre from a dam are 92% more likely to catch the disease than those who live more than five kilometres away.
The contrast is even starker in countries where the prevalence of malaria is unstable, for example due to annual or seasonal variations in temperature or rainfall. In these countries, dams act as a stabiliser for the epidemic, and the risk of contracting malaria is up to 320% higher among people who live within one kilometre of a reservoir than those who live more than five kilometres away.
According to the researchers, dams may be responsible for at least 1.2 million cases of malaria in Africa every year. But the real figure could be as high as two million.
Lack of data forced the team to exclude around 800 other dams from their study, most of which were situated in areas of high malaria prevalence.
Many new dams planned
Based on the figure of 1.2 million cases per year, dams are responsible for under 1% of Africa’s malaria epidemic. This may make them a small factor in the big picture of the continent’s struggle against the disease, but they are no less important on a local level. And as climate change increases the risk of water scarcity, many more dams are planned.
The researchers counted 60 projects in countries with high levels of malaria, which they estimated would cause a further 61,000 cases per year. And these figures do not take into account the fact that dams attract new inhabitants to the area, notably farmers in need of water.
Solomon Kibret’s research team argued that any newly constructed dams should be accompanied by a series of measures to prevent the disease. These measures could include draining the reservoirs during the mosquitos’ reproduction period, financing distribution programmes for mosquito nets laden with insecticide to local populations, or introducing species of fish that eat mosquito larvae.
This article was previously published by EURACTIV France.