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.
Areas with decades of irrigation now see much lower rates of malaria and improved crops. The researchers point to the example of Punjab where it once was home to a strikingly high number of malaria cases and now is one of India’s most successful food producing regions. They say that the high number of cases is likely connected to the early transition into irrigation and the problem subsided years later.
The observations on the long transition phase in Gujarat reinforce the insight that development of water resources requires a strong binding commitment to ﬁnance and implement projects that maintain public health and safety.
Irrigation is a valuable tool for areas with low rainfall, point out the researchers. They cite the benefits of improved farm yields, food security, better incomes and increased access to finance and healthcare.
Implementing irrigation systems should be done in a way that is mindful of the potential health costs, says the paper. Steps can be taken to make it harder for mosquitoes to breed. The researchers suggest intermittent irrigation and periodic flushing of canals as examples of relatively affordable ways to keep mosquitoes away.
“The challenge ahead, then, will be to apply these methods over extensive regions and maintain them for long enough periods,” said University of Michigan Professor of Ecology and Evolutionary Biology Mercedes Pascual.