Infecting Mosquitoes With Bacteria Could Have A Big Payoff

Nov 21, 2019
Originally published on November 21, 2019 6:59 pm

Cameron Simmons is far more familiar with dengue than he would like to be.

"I've had dengue. My family's had dengue. It's a miserable, miserable experience," he says. "It's not one I'd ever want to repeat or have anyone else experience."

Unfortunately, last year nearly 400 million people experienced the viral disease that is so painful it's often called break-bone fever. There's no specific drug to treat the infection; medication is given only for the fever and other symptoms. Severe cases, although rare, can be fatal. And the only licensed vaccine has run into concerns about its safety.

In tropical places where dengue is rampant, annual outbreaks are a huge burden on health clinics.

Simmons is the director of the impact assessment team for the World Mosquito Program. He and his colleagues are trying to make a dent in this persistent disease.

"Throughout Southeast Asia, dengue is a guarantee every rainy season," he says. "And so communities know — and indeed our public health colleagues in those communities know — that what they're doing at the moment doesn't work."

So instead of the old method of trying to trap and kill all the dengue-carrying mosquitoes, the World Mosquito Project is doing the opposite. Scientists are cultivating and releasing mosquitoes, except these mosquitoes are special: They've been infected with a bacterium called Wolbachia.

Wolbachia occurs naturally in many insects, but not normally in Aedes aegypti mosquitoes, which spread dengue. It has to be introduced into the mosquitoes in the lab. But then the bacterium is passed down to future generations. The bacterium appears to block Aedes aegypti from transmitting arboviruses, which include dengue as well as chikungunya, yellow fever and Zika.

"We don't see any change in the population size of the mosquitoes. And they still bite us. So unfortunately we don't solve that problem," Simmons says, laughing. "What we do is solve the problem of those mosquitoes being transmitters of these medically important diseases."

This week, at the American Society of Tropical Medicine and Hygiene annual meeting, Simmons is presenting results of several trials his group is conducting around the world.

"In Indonesia, we've [released Wolbachia-infected mosquitoes in] a community of 50,000 people and compared it to a community that was left without Wolbachia," he says. "We've seen a 75% reduction [of dengue cases] over the last 2 1/2 years in the Wolbachia-treated community."

He says in laboratory studies the group has been able to use this bacterium to completely stop dengue transmission.

The problem in the real world is that other people and other mosquitoes keep migrating into the areas being treated, messing up the experiments. But from a theoretical perspective Simmons sees Wolbachia as potentially a way to wipe out dengue entirely.

"If you had a big island," he proposes, "[and] you stop people from moving in and out of that island, and you put Wolbachia across all the mosquitoes on that island, the science suggests that you'll eliminate dengue in that location."

Some countries are trying to do just that. Australia started using Wolbachia-infected mosquitoes nearly a decade ago to control outbreaks of imported dengue in the state of Queensland.

This year the government of Malaysia launched a campaign called "Wolbachia Malaysia" to attack dengue. This campaign isn't affiliated with Simmons' group, the World Mosquito Program. It uses a different strain of the bacterium but is trying to do the same thing — make the mosquitoes incapable of spreading these viral diseases.

The Wolbachia technique doesn't work with malaria, which is driven by parasites and transmitted by a different kind of mosquito.

This year there's been a record number of dengue cases in the Americas, according to the Pan American Health Organization. Brazil has had more than 2 million cases since the beginning of the year.

"It's amazing. Aedes aegypti is adapted very well to the Brazilian situation," says Luciano Moreira from the Fiocruz Foundation in Brazil. Moreira is also the lead scientist in the country for the World Mosquito Program.

"Aedes aegypti is everywhere," he says. "They can live even in high-rise buildings and in vases and plant pots. Even in a very small amount of water, they will be there and they can survive."

The World Mosquito Program is currently deploying Wolbachia-infected mosquitoes at two sites in Brazil — in Rio de Janeiro and the nearby city of Niterói.

But dengue comes in waves.

Unfortunately from a research perspective, there wasn't much dengue in those areas of Brazil in 2018. But what WMP did see was a big impact on chikungunya.

"We are getting like 70%, 75% less cases [of chikungunya] where Wolbachia has been established," Moreira says.

His daughter contracted dengue in 2016 in the city of Belo Horizonte, the capital of the Brazilian state of Minas Gerais.

"She was ill for 10 days, really bad in bed," he says. "So for me, having the potential of bringing a solution to the community is something that I dream about."

The next place Moreira and his colleagues at WMP are going to deploy their bacteria-infected mosquitoes is Belo Horizonte.

Copyright 2020 NPR. To see more, visit https://www.npr.org.

ARI SHAPIRO, HOST:

Infecting mosquitoes with a naturally occurring bacteria appears to block them from spreading several major tropical diseases, including dengue and Zika. The relatively new approach comes at a time when dengue cases have been rising globally. They're expected to increase even more as climate change expands the range of the dengue mosquito. NPR's Jason Beaubien reports.

JASON BEAUBIEN, BYLINE: Cameron Simmons, with the nonprofit World Mosquito Program, is far more familiar with dengue then he'd like to be.

CAMERON SIMMONS: I've had dengue. My family's had dengue. It's a miserable, miserable experience and not one I - you know, I'd ever want to repeat or have anyone else experience.

BEAUBIEN: Unfortunately, last year, according to the WHO, nearly 400 million people experienced the viral disease that's often called breakbone fever. And in tropical places where dengue is rampant, annual outbreaks are a huge burden on local health clinics. Simmons and his colleagues want to change that.

SIMMONS: You know, throughout Southeast Asia, dengue's guaranteed every rainy season through most of Southeast Asia. And so communities know and, indeed, public health colleagues in those communities know that what they do at the moment doesn't work.

BEAUBIEN: So instead of trying the old method of attempting to trap and kill all the Aedes aegypti mosquitoes, the World Mosquito Program is doing the opposite. They're cultivating and releasing mosquitoes, except theirs have been infected with a bacteria called Wolbachia. The bacteria appears to block the mosquitoes' ability to transmit arboviruses, which include dengue, Zika, yellow fever and chikungunya. Simmons is presenting results this week at the American Society of Tropical Medicine and Hygiene of several trials his group is doing around the world. And he says they're finding the technique effective at reducing dengue.

SIMMONS: In Indonesia, where we've treated a community of 50,000 people, compared it to a community that was a similar community that was left untreated - without Wolbachia - we've seen a 75% reduction over the last 2 1/2 years in the Wolbachia-treated community.

BEAUBIEN: He says in laboratory studies, they've been able to use this bacteria to completely stop dengue transmission, and some countries are trying to do just that. This year, the government of Malaysia launched a campaign called Wolbachia Malaysia to attack dengue. The campaign isn't affiliated with Simmons' group, the World Mosquito Program. But conceptually, it's trying to do the same thing - make the mosquitoes incapable of spreading viral diseases. This year, there's been a record number of dengue cases in the Americas, with Brazil reporting more than 2 million cases since January. Luciano Moreira is the lead scientist for the World Mosquito Program in the country. He says the dengue mosquitos are everywhere in Brazil.

LUCIANO MOREIRA: Because they can live even in high-rise buildings and, like, in vases and, like, plant pots and everywhere, even a very small amount of water, they'll be there. And they can survive.

BEAUBIEN: In 2018, there actually wasn't much dengue in the areas where they released their mosquitoes, so Moreira wasn't able to tell how much of an impact they had on dengue. But they did see a 70% drop in cases of chikungunya, compared to a neighboring area without the Wolbachia-infected mozzies (ph).

Jason Beaubien, NPR News. Transcript provided by NPR, Copyright NPR.