Pinoy scientists use sterile mosquitoes to weed out dengue

Scientists from the Philippine Nuclear Research Institute (PNRI) are fighting dengue by stopping it before it spreads: by preventing mosquitoes from breeding in the first place.

The PNRI's Sterile Mosquito Project, spearheaded by Glenda Obra and her team of entomologists, aims to release special mosquitoes—which have been treated with radiation to make them sterile—into dengue-plagued areas.

It's a simple idea: if mosquitoes can't reproduce, they can't spread the disease.

Mosquitoes breed in wet places. Obra notes that the Philippines is a highly conducive breeding ground for these insects- because of abundant rainfall and loosely-implemented sanitation laws.

“We have a dengue vaccine but that’s for prevention. We shouldn’t just rely on one control method,” Obra says. 

The project is based on the Sterile Insect technique (SIT), a species-specific, environment-friendly method of insect control that has been used successfully in the US, Mexico, and Libya screwworm flies.

Cause for concern

“The Aedes aegypti mosquito is the primary vector of dengue in the Philippines. From 2004 to 2010, we were the 7th country with the highest [number] of dengue cases. From 2013 to 2015, there were more than two hundred thousand suspected dengue cases [in the Philippines],” Obra says, citing World Health Organization (WHO) data. 

According to the Department of Health (DOH), a total of 66, 299 suspected dengue cases were reported nationwide from January 1 to July 16, 2016 alone.

Asked about the status of the Sterile Mosquito Project, Obra said that her team is in the early stages of perfecting SIT for Philippine-based Aedes aegypti.

But so far, it's still mostly a laboratory affair.

Rearing mosquitoes

“We haven't released sterilized mosquitoes in the field. We’re still in the mass rearing stage,” Obra explains, referring to the mass breeding of male and female Aedes aegypti mosquitoes collected from the Old Balara, Quezon City.

One of the fundamental requirements of the SIT is to mass-rear insects in the lab, with the help of artificial diets.

“We evaluate different diets that will give good quality larvae. Female mosquitoes are attracted to the fresh blood of humans and other animals. We’re maintaining two colonies. One colony feeds on the blood of live mice. The other colony feeds on fresh pig’s blood,” Obra says, referring to the two different diets of the female mosquitoes.

At present, Obra's team is experimenting on the diets of the two mosquito colonies.

But there is more that needs to be done.

“In the lab, we need to standardize our mosquito rearing protocols before we can upscale and produce millions of mosquitoes. Several irradiation and mating competitiveness tests must also be conducted before the release of the sterile males in the wild,” Obra explained.

The number of years needed to complete the project depends on numerous factors, including the size of the release area, the population of mosquitoes in the area, the cooperation of the different households, and local government support.

Obra said that her team has proposed a three-year time frame for the project, pending approval by the DOST. — TJD, GMA News