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.
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 Celsius, 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.
“Outbreaks of the illness not only affect families with sudden health care costs and loss of incomes for adults put out of work, but also impact health services, businesses and tourism,” an ADB study said, “straining government budgets due to unplanned spending on large-scale emergency response measures.”
Dengue has become a global problem throughout Southeast Asia in particular although it is now endemic to more than 100 countries. Although intensive work has gone on to produce a vaccine, so far there has been little success. Eliminating the mosquitoes is currently the most effective remedy.
“Around 2.5 billion people worldwide are at risk of contracting dengue, more than 70 percent of whom live in Asia and the Pacific,” the ADB study said. “The threat of exposure to dengue-carrying mosquitoes is rising with uncontrolled urbanization and a surge in the use of non-biodegradable packaging, which can act as a water reservoir for dengue mosquito breeding.
Dengue is spread by a specific mosquito that breeds readily in standing water, such as found in storage containers, flower pots and discarded tires. The guppies are particularly effective in these settings.
“The project was successful in mobilizing communities with widespread grassroots participation, and high levels of acceptance of fish as an effective way of reducing the spread of dengue,” said Dr. Eva Christophel, a WHO specialist in vectorborne diseases. “This project was an important contribution to WHO’s efforts to develop a toolkit of different community-based methods to prevent and reduce the magnitude of dengue transmission.”
