26 August, 2013
From VOA Learning English, this is the Agriculture Report.
Irrigation systems can make a big difference in agricultural production. Irrigation can also improve the lives of farm families. However, the addition of water to the land or soil may cause problems in some areas. A new study describes how irrigation water can lead to an increase in malaria cases that could last for ten years or more.
Malaria is spread by mosquitoes, the insects like to reproduce in standing water. So when a dry area is irrigated, the disease can appear and spread.
Mercedes Pascual is a scientist at the University of Michigan. She and her team studied areas in northern India where irrigation systems were built over a number of years. They compared how malaria progressed with the spread of irrigation.
"What happens is that when you irrigate, there is more, in a sense, more breeding habitats for the mosquito."
She and the other scientist found that after farmers began irrigating their crops, the risk of malaria rose sharply. At first, her team thought maybe the number of cases rose because there was little effort to control the mosquitoes that spread the disease. But they were wrong.
"In fact, we saw the opposite. This transition stage was characterized not just by heightened malaria risk, but also by more intervention to control the mosquito vector."
Even after the mosquito control efforts were in place, the researchers found high rates of malaria continued for ten years or longer.
Mercedes Pascual suggests that the irrigation project supervisors need to work more on reducing places where mosquitoes might reproduce. She also says health officials may need to try other methods of malaria prevention that would work for long periods of time.
"And what we are saying is that those measures have to be sustained, and sustained and also planned for, for the long term."
In the words of the researchers, irrigation offers considerable rewards in areas with low rainfall. But as Mrs Pscual and her team discovered irrigation also can bring years of high rates of malaria. The only way to avoid the problem is through better planning and control measures.
A report on the study was published in the Proceedings of the National Academy of Sciences of the United States of America.
And that's the Agriculture Report from VOA Learning English. You can download transcripts and MP3s of all of our programs at our website, 51voa.com. You can also find captioned videos at the VOA Learning English channel on YouTube. I'm Christopher Cruise.