- What is this issue about?
Zika virus is a mosquito-borne illness that has public-health officials around the world on edge.
- Why is Zika virus a concern?
In Brazil, hundreds of babies born to Zika-infected mothers have suffered severe birth defects since last year and there’s a compelling need for trying to control the mosquito population this way. Aedes aegypti (the main vector in the Zika virus) spreads not only , but also dengue fever, yellow fever, and chikungunya virus. This disease which can spread quickly has no cure and the vaccine is still being developed.
Today, scientists can just tweak the genes of the animal or insect they’re trying to vanquish. There’s good evidence to support the idea that genetic modification of the Aedes aegypti mosquito, for example, could help dramatically reduce its population.
Aedes aegypti is the main vector in the Zika virus. It could open the door for a new era of gene-tweaking for pest control and disease prevention. Oxitec’s plan is to inject mosquito eggs with DNA that contains lethal genes, then release the genetically modified males from that batch of eggs so they can mate with wild females. (Males don’t bite; so releasing only males is a way to make sure the release of these insects doesn’t contribute to the spread of disease.) The offspring of these lab-tweaked males and wild females, having inherited the altered DNA, cannot survive to adulthood. If all goes as planned, the mosquito population should shrink as a result. There’s already good evidence that shows Oxitec’s approach can work. Field tests in Piracicaba, Brazil, resulted in an 82 percent decline of the mosquito population over an eight-month period. Oxitec says, “The very thing we’re releasing is designed to disappear from the environment without a trace.” If Oxitec is successful, its technology could help wipe out Aedes aegypti in the region—and protect people from Zika transmission there.
Oxitec claims its method of mosquito reduction would be more effective than traditional insecticide anyway, and would cost about the same or possibly less.
There would be about 80 to 90 percent reduction of Aedes aegypti mosquitoes.
If you can reduce the mosquito population sufficiently, you can break that transmission cycle.
Genetically modified mosquitoes may have been successful in reducing the Aedes aegypti population in Piracicaba, where Oxitec has expanded its trials to cover an area that’s home to some 60,000 people.
It’s only been tested at a small scale. What about more densely populated areas, or the hundreds of miles of cities and towns along the Gulf Coast?
Is an 80-percent reduction in the mosquito population enough to stop the spread of Zika? It could be that we need a 99-percent reduction to get an impact.
The technology is about controlling the mosquito population, so we don’t make direct claims that we’re controlling the disease.
The level of mosquito suppression that’s needed to stop disease transmission depends on a wide variety of factors, including the mosquito population, the human population, the amount of diseases already circulating, and the proportion of people previously infected, and therefore immune.
The biology of it is incredibly scalable, and ultimately that’s why these bugs are such a problem—because they’re so prolific. This kind of scalability is not just that you could theoretically scale up to country or continental scale.
- The “what-ifs”-
(You can start to fantasize about every possible fate of that gene, but it’s impossible to test all of that in a lab.)
What if, for some reason, it doesn’t work—and reverts back to a wild-type state?
What if the desired gene mutation doesn’t take, and people end up releasing mass quantities of new mosquitoes that end up making the Zika problem worse?
What if, for example, the gene modification ends up altering a mosquito’s behavior—making it more aggressive, or changing its host preference? (In the case of Aedes aegypti, which already prefers humans, a change in host preference might not be so bad.)
What if the mosquitoes end up transferring their altered genes horizontally—to other non-target species, rather than just to their own offspring?
What if there’s sexual transmission of a virus that people barely understand. (Talk about the fear factor).
- To conclude
If you weigh these pros and cons, people might say, genetic modification may be the lesser of two evils. Genetically modified mosquitoes may be “our best hope” for fighting Zika virus. Beyond Zika, mosquitoes pose such an enormous threat to human health, many scientists have argued, that the most sensible thing to do would be to wipe them out—even if the ecological impact is unknowable.