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Sunday, May 29, 2022

Rural California Hatch’s Plan for Engineered Mosquitoes to Battle Stealth Predators

Visalia, Calif. — Brian Ruiz moved his family into a newly constructed home in this Central Valley farming center seven months ago and almost immediately found they were under attack.

Mosquitoes bite and bother them in broad daylight. He looked around, trying to find a water source where they were breeding, and saw a freshly dug pipe meant to drain water from the backyard to the front. He lifted his hat and found a small puddle in the drainage line inside, which didn’t have enough slope to drain completely.

He caught a turkey buster and pulled out the water, already knowing what he would find: the larvae of aedes aegyptiOne of the biggest threats to humans on the planet.

Ruiz knew what he was looking for as he is in charge of a newly formed team that spends the summer months traveling around northern Tulare County to counter the invasion. aedes aegyptiMosquitoes capable of infecting humans with deadly diseases such as dengue, chikungunya, yellow fever and zika.

Since setting foot in California less than a decade ago, aedes aegypti Rapidly spread across the state, its territory ranged from the desert area of ​​what is now Imperial County on the US-Mexico border to the city of Redding in Woody Shasta County, approximately 750 miles north.

to compete aegyptiMosquito control districts rely on the same tools they were using decades ago – eliminating pesticides and water sources – even though climate change and agricultural practices allow mosquitoes to breed in previously uninhabited places.

But Tulare County officials expect the area to soon be a test site for new generation technology, including genetically modified mosquitoes, as they are now common in the Caribbean and areas of Central and South America. Trying to stop the spread of disease. aedes aegypti is extensive.

The most immediate mosquito threat in Tulare County comes from a different genus, culex, a type that usually bites at dawn and dusk and can carry West Nile virus, St. Louis encephalitis, and Western equine encephalitis viruses, all of which can be fatal. Over the past decade, California has recorded more than 4,000 West Nile cases and at least 220 deaths. Tulare’s mosquito control districts have poured extensive resources into that fight, including releasing a range of chemicals, maintaining a hatchery for the larvae-eating fish and, most recently, drones to carry pesticides deep into corn fields. Buying is included.

aedes aegyptiHowever, it is a growing concern, and it is very difficult to combat.

Delta Mosquito and Vector Control Supervisor Rick Alvarez of the Vector Control District investigates an abandoned backyard pool in Tulare County that has become a breeding ground for mosquitoes. (Anna Maria Barry-Jester/Kaiser Health News)
computer screen
The Delta Mosquito and Vector Control District in Tulare County tracks locations where mosquitoes have been reported so technicians can respond and work to curb populations by removing water sources and spraying insecticides. (Anna Maria Barry-Jester/Kaiser Health News)

To understand this fight, you have to first understand how much theft is hidden. aedes aegypti Is. Mosquitoes can lay eggs in spaces as small as a bottle cap, and females spread their eggs in many places – scientists often refer to their “secret habitat”. The eggs of most other types of mosquitoes require water to survive, but aedes aegyptiMay lie dormant for months, spring to life when water finally arrives. And a mosquito can bite multiple times, repeatedly snacking on the same person, or passing from one to another. If one of those people gets dengue or some other virus then they become a fatal threat.

In an increasingly globalized world, people regularly travel to places where dengue is endemic and bring it back to the US. If a mosquito bites them, the disease can spread locally. The same thing happened in the Florida Keys in 2020 and more than 70 people were infected before the outbreak stopped.

California avoids local outbreaks of diseases so far aedes aegypti, But it does matter to imports—California has recorded seven cases of imported dengue this year—and with mosquito populations surging, experts say it’s only a matter of time.

aedes aegypti A frequent flier, traveling the world in cargo. There is no doubt that it has been introduced millions of times in California. But it wasn’t until recently, said Chris Barker, an associate professor of pathology, microbiology and immunology at the University of California-Davis. It was first found in 2013 in three California cities: Menlo Park, Clovis and Madera.

today, aedes aegypti It has spread to more than 200 California cities and 22 counties. And it has strained mosquito control districts. “It’s a lot of extra work, extra staffing, extra financial demand,” Barker said. “And regardless of disease risk, a big issue is bite infestation.”

Because of the danger of mosquitoes, when aegypti Detected in 2014 by the Delta Mosquito and Vector Control District, where Ruiz works, the district rushed to stamp out the threat. The method of its elimination requires searches at every nook and corner of the area where aedes aegypti Several times a week the houses and water sources were cleaned. The district’s assistant manager, Meir Baer-Johnson, said people were so annoyed with the full-court press that it took nearly five years for the community to reappear. Which was a problem, because the district partly depends on residents’ reports of where the mosquitoes are.

mosquito in a container
Caught mosquitoes, including Culex quinquefasciatus pictured here, are tested for disease and insecticide-resistance. In California’s Central Valley, Aedes aegypti mosquitoes have developed widespread resistance to pyrethroids, a family of chemicals often used to kill adult mosquitoes. (Anna Maria Barry-Jester/Kaiser Health News)

The abolition was also short-lived. In 2015, aedes aegypti was resumed, and this time the brutal bites spread to Visalia, the largest city in the region. Because aedes aegypti Now found around the Central Valley, eradication no longer seems like an option, said Mustafa DeBoun, an entomologist who moved from Harris County, Texas, in March 2020 to lead the Delta District.

aedes aegypti Mosquitoes in the area are also widely resistant to pyrethroids, a family of chemicals often used to kill adult mosquitoes. Pyrethroids are in heavy use among agricultural companies in the area, possibly contributing to what Barker described as nearly 100% resistance.

This is why Deboun and his colleagues are interested in the genetically modified mosquito. His hope is that engineers reduce numbers of mosquitoes in the wild aedes aegypti When they interbreed and produce short-lived offspring.

The US Environmental Protection Agency recently approved a test in the engineered mosquito Tulare, made by a company called Oxitec. The company says its latest product releases only male mosquitoes, which unlike females do not bite. Mosquitoes are genetically modified to carry a “self-limiting” gene that is passed on during reproduction and theoretically prevents the offspring from surviving to adulthood. They have been released in several places including Brazil and the Cayman Islands.

He was also released in the Florida Keys last year. There, Oxitec faced backlash from some homeowners who were concerned about the unexpected risks of releasing genetically modified insects into the wild. Local officials put the issue on the 2016 ballot, and county residents, who had suffered both dengue and Zika by then, voted to go ahead.

Now, Oxitec and Delta Mosquito District are waiting for permission from the California Department of Pesticide Regulation to launch the insects. The work will be funded by Oxitec, DeBoun said, with operational support from its employees.

The goal is to build on earlier research, which shows that the revised aedes aegypti Temporarily reduces wild mosquito populations, but has left scientists with questions about the wider impacts on the environment and how well efforts work in the long run to reduce the disease. What is in the unknown is whether Oxitec mosquitoes are in fact unable to produce viable offspring with wild females.

Another question, said Barker, a UC-Davis specialist, is what happens when Oxitec’s mosquitoes encounter tetracycline in the wild. Tetracycline is an antibiotic commonly used to control infections in livestock and agriculture, both of which are found in abundance in the Central Valley. Oxitec mosquitoes are born with a type of off-switch that turns off self-limiting genes when exposed to tetracycline. In the lab, this off-switch allows the company to breed engineered mosquitoes. If it is introduced into the wild, the concern is that the mosquito offspring will not die.

Mustafa Deboun has a prototype of the product
Mustafa Deboun, general manager of Delta Mosquito and Vector Control District, has a prototype for the mosquito-elimination product Oxitec, which it hopes to eventually sell directly to American consumers. If everything goes according to plan, consumers will add water, and the company’s engineers will bring the mosquitoes to life. (Anna Maria Barry-Jester/Kaiser Health News)

On a broader scale, Barker said, he expects California to track the experiment independently. He is among researchers who are concerned about leaving that analysis in the hands of a private company that stands to profit. “If an independent source and company are all in agreement on having the results, it has a lot of power and a lot of potential for the future,” Barker said.

Rajeev Vaidyanathan, director of US operations for Oxitech, said Tulare’s Delta Mosquito and Vector Control District were among several districts willing to host the trial. Among the selling points was Debon’s enthusiasm for new technologies.

Debon previously helped run trials in Houston of a product called Mosquitomate, which releases male mosquitoes infected with the bacteria wolbachia, Mosquitoes Mate When mosquitoes breed with wild females, they produce eggs that do not hatch. Those mosquitoes were also tested in Fresno County in 2018 and 2019 and resulted in a 95% reduction in females aedes aegypti, according to a study on the test. Still, that Mosquito District told The Fresno Bee that it didn’t have the money to continue the project.

“These are great, great options,” said Eva Buckner, an assistant professor at the University of Florida who advises Florida’s mosquito control districts. “I think they have a lot of potential.” She wants to know what the cost-benefit ratio will be for widespread use by government agencies compared to other interventions — a question Tulare research can help determine. And regardless of the price, he cautioned, there isn’t going to be a silver bullet for mosquitoes, which have been on Earth for millions of years.

Oxitec wanted to test its technology in central California, Vaidyanathan said, because it could show it could work full-time. aedes aegypti– Invaded the Southwest. Oxitec hopes that its mosquitoes will eventually be sold in mosquito control districts in the US and directly to US consumers. That option is already available in Brazil through a consumer subscription service, which costs $10 to $30 a month. In the American prototype, the mosquitoes would come in a hexagonal box decorated with playful insects. If everything goes according to plan, consumers will simply pour water, and the mosquitoes will come to life.

This story was produced by KHN, which publishes California Healthline, an editorially independent service of the California Health Care Foundation.

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