Mapping how malaria risk changes as new dams go up

by Chris Samoray
Thursday, April 17, 2014

Malaria is considered a leading public health problem in Ethiopia, with almost 70 percent of the country’s total population of more than 90 million people at risk from the deadly disease. Now, researchers are studying how hydroelectric dams affect malaria prevalence by combining computer simulations with field data from the Ethiopian countryside. The hope is that the new research could provide fresh insight for malarial management programs.

Currently, Ethiopia uses only about 4 percent of its hydroelectric power potential, but in the last two decades, there has been a huge push to develop more hydroelectric power in Ethiopia, says Noriko Endo, a doctoral candidate in civil and environmental engineering at MIT. But constructing hydroelectric dams changes the way water flows and pools in the surrounding landscapes, Endo says. “If you have hydropower electric dams, then you always have an impoundment behind it … and those reservoirs are breeding habitats for mosquitoes.” Thus, she says, hydroelectric dams could expose the local population to a higher risk of malarial infection.

To determine how much hydroelectric dams might increase malarial risk in Ethiopia, Endo examined the impact that the Koka Reservoir — located about 70 kilometers from the country’s capital, Addis Ababa — had on malaria incidences in the surrounding communities using a modified version of a simulator called HYDREMATS (HYDRology, Entomology and MALaria Transmission Simulator). The simulator allowed Endo to explore whether simulations reflected field observations and could thereby have implications in malaria management strategies.

Endo collected and analyzed field data from two Ethiopian villages near the Koka Reservoir: one village was adjacent to the reservoir and the other was 12 kilometers away. The data included daily temperature readings, soil moisture levels, mosquito larvae and mosquito population counts — important, Endo says, because “to implement environmental management [strategies], you have to understand the ecosystem of mosquitoes.”

Endo then used the HYDREMATS model to simulate and examine the differences in hydrology and mosquito population between the two villages. The model simulated rain-fed pools, groundwater pools and reservoir shoreline breeding sites as well as the mosquito population of the villages. Additionally, Endo was able to focus in on the behavior of an individual mosquito in various developmental stages.

Both the field observations and simulations showed similar results, Endo reported at the annual meeting of the American Geophysical Union in San Francisco last December. In each case, she found that the village nearest the reservoir was shown to have a larger mosquito population and prolonged mosquito season, heightening the risk of malaria infection the closer a person is to the reservoir. The findings echo those of other researchers, Endo says, who have also conducted malaria studies around the Koka Reservoir. Those researchers found that malaria occurrence for people who lived within 1 kilometer of the Koka Reservoir was 2.9 times higher than those who lived between 1 and 2 kilometers away, 3.7 times greater than those who lived 2 to 5 kilometers away, and 19.9 times higher than those who resided 5 to 9 kilometers from the reservoir.

There could be a couple reasons for the findings, says William Jobin of the tropical disease consulting group Blue Nile Associates. One could be that more humans could be moving near the reservoirs. His team observed increased malaria levels around the Manantali Dam in Mali soon after a reservoir was filled. The team found a malaria parasite common in reservoirs, he says, but they also noted that new settlements had sprung up near the reservoir. “The second part of this is important,” Jobin says. “The reservoirs produce mosquitoes, [but they] also attract people who settle around them because of the water and fish.” More people plus more mosquitoes is a recipe for more malaria.

Four million to five million people are affected each year by malaria in Ethiopia. Current approaches to managing the disease are materialistic — involving medicines, to which mosquitoes can become resistant, or sprays and netting, Endo says. It would be nice to instead rely more heavily on environmental management, she says, which can help to alleviate some of the need for foreign aid.

“Economically, the temporary methods [to prevent or treat malaria] using drugs and biocides are unsustainable as they require repetition every year,” Jobin says. Although environmental strategies like Endo is studying “might require a larger initial investment,” Jobin says, “they are much more durable and last for many years.”

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