Sterile mosquitoes best weapon against Zika virus. But will program continue?

Mosquitoes released in Clovis for Zika test

Consolidated Mosquito Abatement District began using sterile male mosquitoes in the fight against Zika in 2016, when staff released 20,000 sterile male mosquitoes in a test to control mosquito populations.
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Consolidated Mosquito Abatement District began using sterile male mosquitoes in the fight against Zika in 2016, when staff released 20,000 sterile male mosquitoes in a test to control mosquito populations.

A Fresno County experiment to trick female mosquitoes to mate with sterile males has been so successful in reducing the number of mosquitoes that can carry Zika and dengue viruses that it could become a staple in the mosquito-fighting world, if funding can be found to expand it.

The Aedes aegypti mosquito, a day-biting mosquito, has proven difficult to suppress with traditional mosquito-control techniques, such as spraying. But the field study, which mated female Aedes aegypti mosquitoes with sterile males, reduced the number of biting females by more than 95 percent during peak mosquito season.

The 2018 study results are encouraging, said Jodi Holeman, scientific services control director at Consolidated Mosquito Abatement District in Clovis. “With all the other strategies and control methods that we’ve put toward this mosquito there hasn’t been a single one that has been as effective as the release of the sterile mosquitoes.”

Zika is a virus that can cause severe birth defects. The study in Fresno County “is an important validation of a new approach to controlling these mosquitoes with a dangerous potential to transmit human disease,” said Jacob Crawford, senior scientist at Verily, a sister company to Google.

The Fresno study has helped Verily achieve good results in a study in Australia, Crawford said. And releases of sterile male mosquitoes is happening now as part of a study in Singapore.

A female Aedes aegypti mosquito, known to be a carrier of the Zika virus, acquires a blood meal on the arm of a researcher. Andre Penner Associated Press

“We are energized by what we achieved this year and look forward to bringing this technology to communities most burdened by Aedes aegypti throughout the world,” Verily says in a statement.

The Fresno County sterile-male mosquito study was a collaboration with DeBug Fresno, a project of Verily; MosquitoMate, a Kentucky-based biotechnology company; and the Consolidated district.

MosquitoMate developed a mosquito colony infected with a Wolbachia bacterium that rendered the males sterile. DeBug Fresno created a system of rearing millions of the sterile male mosquitoes and shipping them to Clovis. Consolidated workers released the altered males and monitored the mating results.

15 million mosquitoes

A little more than 15 million sterile male mosquitoes were released in Fresno County in batches at Harlan Ranch, the Loma Vista neighborhood in northeast Clovis and at Fancher Creek in southeast Fresno. The scheduled releases began in April and lasted six months. A fourth neighborhood was added mid-season and was not a part of the study results. Releases there are ongoing in the area of about 700 homes around Herndon and Temperance avenues.

The research relies on the fact that female mosquitoes mate only once in their short lives (they live for a couple of weeks) and with millions of Wolbachia-altered males in the air, the chances of females hooking up with them increases.

This is the second year that DeBug Fresno sent bacteria-neutered male mosquitoes to Fresno County. About 7 million mosquitoes were released in 2017, and the results were a 68 percent reduction in the biting females.

This year, in addition to releasing more than double the 2017 number of mosquitoes, the altered males were released in mid-April before the “wild” mosquito population could reproduce in large numbers, Crawford said. But suppression could have been greater except large numbers of “wild” mosquitoes from neighboring areas flew into the treated neighborhoods, he said.

Do it again in 2019?

Consolidated would like to release sterile-male mosquitoes in the same Fresno County neighborhoods in 2019, and expand the releases to neighboring areas, Holeman said. “Getting a 95 percent suppression is definitely a control strategy that we want to try and continue and apply in our district..”

So far, the release of sterile male mosquitoes has been approved under a federal Environmental Protection Agency experimental use permit. Holeman said the district would need the EPA to extend the permit in 2019.

Up to this point, funding for the research has come from Verily. Consolidated does not have the money to continue the project on its own. The district is seeking funding from other sources, Holeman said. “We are working very hard to bring this program back in 2019 and expand it, if possible.”

If the research project ends and the district cannot release sterile male mosquitoes, Holeman said it will be more important than ever for “every single resident in this community to really be mindful of what water is on their property that can breed mosquitoes.”

Barbara Anderson: 559-441-6310, @beehealthwriter