How science could wipe out disease-carrying mosquitoes and save lives
Mosquitoes kill hundreds of thousands of people every year by spreading disease in tropical areas. They’re also the worst part of many cottage weekends and camping trips in North America.
But it doesn’t have to be that way.
Scientists are developing two methods for eliminating mosquitoes that carry disease, which could be deployed sometime within the next 15 years.
The first, dubbed the sterile insect technique, could be used to kill off disease-carrying mosquitoes in urban areas.
The method involves releasing huge swarms of sterilized males — which don’t bite humans — to mate with wild females. The resulting offspring don’t hatch, and the mosquito population temporarily nose-dives for the season.
The second method, called a “gene drive,” is a much more permanent solution to the problem. It uses gene-editing to render the entire species infertile.
Eliminating one species of mosquito likely wouldn’t have a major impact on the balance of an ecosystem, ethics researcher Jonathan Pugh says. He points out there are thousands of species of mosquito, and only a few that spread disease.
“These techniques aren’t looking to wipe out mosquitoes per se — they’re only looking to wipe out certain species,” Pugh said.
“What we should be trying to do is ensure that we get the balance right,” Pugh told Global News from the University of Oxford in the U.K., where he is a postdoctoral research fellow in applied moral philosophy.
“Yes, the technique poses risk, but there’s also a goal at stake here which is of huge moral value. Namely, the prevention of mosquito-born diseases.”
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Death on wings
Certain breeds of the insect can carry a wide range of harmful or deadly diseases including malaria, Zika virus, chikungunya, West Nile virus and dengue fever.
The deadliest disease of the bunch, malaria, infected 216 million and killed approximately 445,000 people in 2016, according to the World Health Organization. The vast majority of cases — an estimated 90 per cent — afflict people in Africa, and kill far more children than adults.
“In 2016, nearly half of the world’s population was at risk of malaria,” the WHO says.
The second-richest man in the world, Microsoft founder Bill Gates, has made it his mission to eradicate the disease through the Bill and Melinda Gates Foundation. But even his wallet hasn’t been enough to get the job done.
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Nevertheless, Gates has predicted that malaria — and the mosquitoes that spread it — will be eradicated by 2040.
Here’s why it could happen sooner.
Solution 1: Sterilize small mosquito populations
The sterilized insect technique will never wipe out a breed of mosquito for good, but experts say it can be used to control disease-spreading mosquito populations around urban areas.
This could help tropical cities cut down on the spread of deadly diseases, Pugh said. It could also be used to prevent the spread of other mosquito-born illnesses in North America.
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A recent experiment in Australia showed that releasing millions of sterile males can effectively cut the local population of mosquitoes by more than 80 per cent. The experiment targeted the Aedes aegypti mosquito, which is responsible for spreading dengue fever in the country.
The sterilized insect technique dates back to the 1950s, and has been dubbed an “environmentally friendly” pest-control strategy by the International Atomic Energy Agency. Radiation is often used to sterilize insects for the process, although the Australian trial used bacteria for its own purposes.
The U.K.-based research firm Oxitec has also been working on so-called “friendly” mosquitoes, which have been genetically modified to produce offspring that die early.
However, researchers say it’s impossible to rear enough sterilized males to wipe out malaria across the whole of Africa.
That’s why researchers have shifted their attention to gene drives.
Solution 2: Driving mosquitoes to extinction
Gene drive technology is only a few years old, but it’s already become a major focus in the effort to eliminate malaria.
“You put [the gene drive] into a mosquito and that element can spread itself into all of the members of the population on its own,” said Andrew Hammond, a molecular biologist at the Imperial College London.
Hammond is part of a team trying to eliminate malaria-transmitting mosquitoes in Africa through the use of a gene drive. They want to use the gene drive to pass on a trait that will render all mosquitoes infertile within a few generations.
“Our genetic modification will make females sterile, but only if they inherited it from two parents,” he said.
“If they inherited that modification from just one parent, they’ll be completely fine, so the genetic element can spread faster than it makes them sterile,” Hammond said.
His team recently found that a gene drive could reduce the fertility rate in a mosquito population by more than 90 per cent, with the remainder surviving through various mutations. Their findings were published in the journal PLOS last October.
The whole process is made possible through the use of CRISPR, a technique that attempts to effectively cut and paste the genes of living organisms.
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However, tampering with an ecosystem could have unforeseen consequences, giving rise to another mosquito that might also mutate to spread the same diseases, Pugh said.
Kill a few, or kill them all?
Gene drive technology won’t be ready until approximately 15 years from now, Hammond says.
In the meantime, he suggests the sterile insect technique might be the best solution for curbing the spread of disease in populated areas, along with established methods such as vaccines and mosquito nets.
Pugh says it will be important for scientists to promote the use of gene-drive technology over the next decade, so that bans aren’t put in place to prevent it from ever being used.
Some environmental activists have already called for a global moratorium on gene drive technology. However, the notion was rejected by the UN at a biodiversity meeting in late 2016.
Hammond says the gene drive could be rolled out sooner than 2033, but it’s important to make sure the technology has been fully tested before it’s unleashed.
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Hammond says there’s no going back with the gene drive, because it will ignore borders and spread throughout the continent wherever it’s deployed.
“It’s something that you can’t easily take back once you release it,” Hammond said.
That’s why lawmakers will have to decide ahead of time whether saving millions is worth the risk of releasing an extinction gene into the world, Pugh said.
“There is going to be something of a gamble,” he said.
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