Because of the pathogens they carry, mosquitoes are responsible for more human deaths each year than any other animal, including other humans. But very few of the 3,500 species of mosquitoes actually transmit deadly diseases to humans. So what if we could get rid of the most deadly mosquitoes?
Over the past two decades, scientists have begun experimenting with engineered technologies called "gene drives" that could theoretically do just that. So, should we? To begin to tackle this question, we need to understand how technology works.
In the normal process of inheritance, the genomes of each parent are randomly recombined. So their offspring end up with DNA that is a 50/50 mix from their parents. But gene drives thwart this process and ensure they keep moving.
Gene drives are found in nature but, using new gene editing technology,
scientists have also begun engineering them in labs. For example, in a 2018 study, researchers injected mosquito eggs with a gene drive that made the female sterile when they had two copies of the modified gene.
Such modifications will usually disappear quickly. But it spread. The mutated mosquitoes passed on the gene drive to some of their offspring.
The gene drive, which they inherited on one chromosome, replicated itself on the other chromosomes in the offspring's sperm and egg cells, ensuring that it would be passed on to their offspring, regardless of Which chromosome they got.
The process was repeated so that all males who carried the gene and all females who had a copy of it continued to reproduce, spreading the gene drive. As they did, they produced more females who had two copies of the gene—and would therefore be sterile.
With an almost 100% inheritance rate, the gene spread through the population and within 12 generations almost all females were sterile, and the population collapsed. In 2020, the same team achieved a similar result with a gene drive that made the population male-only.
Gene drives have proven powerful in the lab.
So, implementing them in the wild is a big decision—one that's being considered because of how the fight against mosquito-borne diseases is going.
Current mosquito control measures, such as insecticide-treated bed nets, helped reduce the number of deaths from malaria, the deadliest mosquito-borne disease, between 2000 and 2019. But deaths have started to rise again.M
any mosquitoes have developed resistance to insecticides—and insecticides kill more than just mosquitoes. In addition to the first malaria vaccine approved in October 2021, many see promise in gene drives.
Experts are researching what it would look like to specifically target the deadliest mosquito populations with this technology. Like Anopheles gambiae, for example: the species most responsible for spreading malaria in equatorial Africa, which experiences the majority of mosquito-related deaths.
The idea is that, when the gene-driven population of Anopheles gambiae is reduced enough, it will break the cycle of malaria transmission. But before gene-drive mosquitoes can actually be released into the wild, some big questions need to be answered.
For example, can crossing gene drives cause the extinction of non-target species?
Many mosquito species don't seem to interbreed,
which makes it unlikely, but scientists are doing research to make sure. And how might a decline in mosquito populations affect ecosystems?
A team is examining the droppings and stomach contents of insectivores in Ghana to assess the role of Anopheles gambiae in local food webs.
And researchers are investigating whether suppressing populations could put other pests at greater risk or leave a niche open for a harmful species to occupy. Scientists are also looking for alternatives to depopulation, such as gene drives that make mosquitoes resistant to the malaria parasite.
And others are taking countermeasures to reverse the effects of gene drives when needed. Meanwhile, some have called for a halt to gene drive research out of concern for potential consequences.
This raises another question:
Who decides whether to release gene drives?
It is important that communities, scientists, regulators and governments in countries most affected by mosquito-borne diseases are heavily involved in the research and decision-making process.
Discussions are currently underway at all levels to establish a system to regulate this new field of research.
Comments
Post a Comment