A Google plan to wipe out mosquitoes appears to be working

An experimental program led by Google parent Alphabet Inc to wipe out disease-causing mosquitoes succeeded in nearly eliminating them from three test sites in California's Central Valley.

Stamping out illness caused by mosquitoes is one of Alphabet unit Verily's most ambitious public-health projects. The effort appears to be paying off, according to a paper published in the journal Nature Biotechnology on Monday. 

Verily is also running coronavirus triage and testing in parts of California. Bradley White, the lead scientist on the Debug initiative, said mosquito-suppression is even more important during the pandemic, so that outbreaks of mosquito-borne diseases such as dengue fever don't further overwhelm hospitals.

Since 2017, the company has released millions of lab-bred Aedes aegypti male mosquitoes into several Fresno County neighborhoods during mosquito season. The insects are bred in Verily labs to be infected with a common bacterium called Wolbachia. When these male mosquitoes mate with females in the wild, the offspring never hatch.

In results of the trial published on Monday, Verily revealed that throughout the peak of the 2018 mosquito season, from July to October, Wolbachia-infected males successfully suppressed more than 93% of the female mosquito population at field test sites. Only female mosquitoes typically bite.

Working with the local mosquito abatement district and MosquitoMate, which developed the mosquitoes originally, Verily released as many as 80,000 mosquitoes each day in three neighborhoods from April 2018 through October 2018. In most collections, per night Verily found one or zero female mosquitoes in each trap designed to monitor the population. At other sites without the lab-bred bugs, there were as many as 16 females per trap.

"We had a vision of what this should look like and we managed to do that pretty perfectly," said Jacob Crawford, a senior scientist on the Debug project.

In the arid climate of the Central Valley, disease is an unlikely result of a mosquito bite. But in the hot, humid regions of the tropics and subtropics, diseases caused by the Aedes aegypti, such as dengue fever, zika virus and chikungunya, kill tens of thousands of people every year. Releasing masses of Wolbachia-infected mosquitoes into the wild might wipe out entire populations of deadly mosquitoes and the diseases they carry.

Verily is not the only organization pursuing an end to mosquito-borne disease. Microsoft Corp co-Founder Bill Gates has pledged more than $1 billion to help wipe out malaria, including controversial efforts to genetically modify mosquitoes. Infecting mosquitoes with Wolbachia, which occurs naturally in some mosquito species, is a popular approach rooted in an old insect control strategy called sterile insect technique. 

What Verily's efforts offer is not just evidence that Wolbachia can help wipe out disease-causing mosquitoes but potential ways to make such efforts work on a massive scale. Last year, Verily released about 14.4 million mosquitoes in Fresno County.

Initial small-scale Fresno trials in 2016, run by an upstart called MosquitoMate, were the first time male Aedes aegypti mosquitoes infected with the bacteria were ever released in the US. The following year, Verily stepped in, bringing more advanced technology to the breeding and release process that could make it possible to expand such efforts to entire cities or regions.

The new paper details many of those technologies, such as an automated process for separating male and female mosquitoes in the lab, and software that helps to determine exactly where to release altered male mosquitoes for maximum effectiveness.

"Once you try to start rearing hundreds of thousands of mosquitoes a week, you run into all sorts of problems," said White. "Mosquitoes may be everywhere, but they are really finicky and difficult to grow."

Verily has expanded its partnerships to include Singapore's National Environment Agency. Trials there have entered a fourth phase to cover 121 urban residential blocks and about 45,000 residents. Verily is eyeing partnerships in South America and is in talks to launch in the Caribbean.

Within a few years, said Crawford, Verily hopes the program will cover entire regions. Without intervention, he said, the public health toll of mosquito-born illness will only grow.

"This is something that's not going away on its own," he said.