Guppy fish—a colorful species just 3 to 4 centimeters in length—are being heralded as a potential way of preventing dengue fever outbreaks in Cambodia.

The Malaria Consortium just wrapped up a yearlong pilot program in Kompong Cham province that set out to find the most cost-effective way of preventing outbreaks in a country that has one of the highest per-capita dengue incidence rates in Southeast Asia.

The project zeroed in on the gup­­py, a tropical fish—referred to as the “seven-colored fish” by Cambodians—that feeds on the larvae and adult Aedes aegypti mos­quito, which carries the virus, and thrives in stagnant water.

In the trial, guppies were added to household containers holding at least 50 liters of water, such as drums and water jars. When the water was tested throughout the trial, those households with fish had less than half the adult mosquitoes of those without.

With no vaccine or widespread treatment currently available in Cambodia, prevention that relies on controlling mosquito populations is the best alternative, according to Rabindra Abeyasinghe, a World Health Organization specialist. “Even if we have vaccines, we still need vector control,” he said on Thursday. “Aedes flourishes better in our cities than we do.”

Mr. Abeyasinghe, whose organization endorses the Malaria Consortium’s project, said guppy fish are the best solution for Cambodia at the moment.

The “guppy fish doesn’t pollute the environment—we are happy to be a part of that,” he said, adding that the scale and frequency of den­gue outbreaks will fall under the plan, reducing the dependency on pesticides.

There were 14,303 reported cases of dengue in Cambodia last year, and 35 deaths, National Den­gue Control Unit program manager Rithea Leang said at a news conference organized by the Ma­la­ria Consortium in Phnom Penh on Thursday.

According to the consortium, an international NGO that focuses on the control of communicable diseases, about 13 percent of the cases were found in Kompong Cham province, the location of its trial.

Mr. Leang said the current na­tional strategy was to treat water in dengue-prone areas with larvicide once a year. However, John Hus­tedt, the project’s senior technical officer, said this is only done once an outbreak—which is defined by the government as three or more cases in one village—is identified.

Despite acknowledging that the government’s current plan is more costly than using guppy fish, Mr. Leang said his department, which he repeatedly stressed did not have a big budget, was “not convinced” that the fish were a long-term alternative.

“We don’t know how sustainable it is yet—it is too early,” he said, add­ing that they were concerned about the plan’s practicality and manageability.

Marian Blondeel, a spokeswom­an for the consortium, said the government still “believes there is some value in conventional methods,” including the use of larvicides and insecticides. “They do see the benefits [of guppy fish], but change is always hard.”

Although Mr. Leang seemed hes­­itant about the new strategy, Yves Bourny, country director for the Malaria Consortium, said it was always his organization’s in­tent to raise the funds for a national roll-out.

It would cost about $1 million to expand the plan to 2 million people across five provinces that are most prone to dengue outbreaks, but donors are interested in supporting a plan that is more effective and sustainable than insecticides, he said.

“There is evidence that there could be resistance to insecticides,” Mr. Bourny said. “The era of insecticides is over.”

Ms. Blondeel said community members involved in the pilot program were big fans of the fish—and not just because of the hard data.

“We asked the communities what they thought of [the project], and they all said they really like the fish—they see the fish as an omen of good luck in Buddhism,” she said.

Kim Sourphirum, director of Kompong Cham’s provincial health department, said dengue cases in the province had gone down from last year—1,031 cases were reported this year, compared to 1,556 last year—but he could not confirm a direct link to the gup­py project.

“It’s a good project because the guppy fish can kill mosquitoes be­fore they are born,” he said. “I hope the plan keeps going.”

Thai Sokheng, a 53-year-old from Kompong Siem district’s Choeung Kuok village, which was one of the areas treated with gup­py fish, said villagers did not trust the conventional dengue control method.

“They used to complain and wor­ry about larvicide,” Ms. Sokheng said. “In my area, many villagers support having guppy fish.”

“I hope this project continues forever,” she said.

(Additional reporting by Sek Odom)

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