Dengue vs. Guppies: colorful fish a cheap effective tool

Dengue    The lowly guppy, unassuming inhabitant of many a child’s fishbowl, could become an unlikely combatant to slow the spread of dengue, an agonizing, mosquito-borne illness giving rise to hundreds of thousands of severe cases every year, including up to 20,000 deaths worldwide.

A trial study conducted by the governments of Cambodia and the Laos, supported by the Asian Development Bank, which provided a grant of US$1 million, and the World Health Organization resulted in a sharp decline in mosquito larva in water storage containers after the tiny fish were introduced into them.

A similar method was employed in New Orleans after Hurricane Katrina in 2006. Tiny fish were placed in flooded swimming pools to keep down the mosquito breeding rate. Pic: AP.

The key was convincing communities to accept fish in their water containers, according to the ADB, with residents wary of the tiny fish swimming around in their water storage jars. But, according to the report, guppies don’t harm water quality and can survive on microscopic organic material in the absence of mosquito larvae. At the project close in Cambodia, 88 percent of the storage containers in the project contained guppies, with the figure at 76 percent in the Laos study.

“This is a low-cost, year-round, safe way of reducing the spread of dengue in which the whole community can participate,” said ADB health specialist Gerard Servais. “It offers a viable alternative to using chemicals and can reduce the scale of costly emergency response activities to contain epidemics.”

The diminutive fish are ideal for the purpose, being prolific reproducers. The gestation period is 21 to 30 days, the female dropping up to 50 fry at a time. They prefer water temperatures of 20-27 degrees celcius, ideal for tropical climates. They eat just about anything including flake foods, rine shrimp, algae – or mosquito larvae.

The trial was conducted in two districts, one in Cambodia and the other in Laos from 2009 to 2011, resulting in a sharp decline in mosquito larvae. Guppies eat larvae that grow into mosquitoes, which in turn infect humans with dengue, an enormously painful infectious tropical disease also known as bonebreak fever because of the deep muscle and joint pain it causes. Victims have been known to lose as much as 10 kg in a few days because of the fever and other ailments it causes. It can develop into dengue hemorrhagic fever and possibly dengue shock syndrome, leading to death if it is not treated properly.

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