16 August 2013

Unintended Consequences: Irrigation Canals and Malaria

Mosquitoes and plants thrive where there is water. Farmers in arid regions who use irrigation systems to collect water also construct a mosquito breeding ground.

New research shows that irrigation systems malaria prone areas can cause an increase in local malaria risk that lasts for more than a decade. Even when health authorities mount a response to kill off mosquitoes using insecticides, the problem of malaria is still worse than before the open water.

“In these dry, fragile ecosystems, where increase in water availability from rainfall is the limiting factor for malaria transmission, irrigation infrastructure can drastically alter mosquito population abundance to levels above the threshold needed to maintain malaria transmission,” said lead author and University of Michigan graduate student Andres Baeza.

Baeza and her team studied cases of malaria in northwest India. Infrequent and inconsistent rain makes for more challenging farming and is why farmers employ various irrigation methods to ensure crop health. The study looked at the effects of a large irrigation project that will provide enough water to cover more than 47 million acres.

It is known that introducing irrigation to arid locations leads to an increase in malaria risk. The original thought was that malaria risk subsided rather quickly as families improved thanks to better farming conditions. This new research shows that is not quite the case. Irrigation does increase vegetation when it is introduced, meaning farms are doing much better. However, malaria risk persists for years after the introduction of the irrigation.

The researchers found that the areas that were transitioning to irrigation systems had higher malaria risk and also were where the most anti-malaria activity was taking place. India uses indoor residual spraying to clear mosquitoes from homes in the transition areas, but that has not been enough to eliminate the new risk.

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