Changes to one part of a complex system can lead to dramatically different changes in other parts.
While gene drive technology has only been used in small trials so far, the potential for far-reaching unintended consequences is enormous. This gene technology could remove whole species from ecosystems. Which could be great for tackling problems like malaria. But wiping out species in the past has had it’s problems. The extermination of sparrows in China from 1958 to 1962 resulted in severe ecological imbalance and widespread famine, and acts as a cautionary tale.
Let’s complicate things
We could change the genetic makeup of a mosquito. Make it so they can’t spread malaria to people. Making one, or even hundreds, in the lab is possible right now.
Spreading a genetic change from mosquitos in the lab to billions and billions of wild mosquitos is a challenge that needs a new type of technology. The gene drive.
Usually if you released a genetically modified mosquito and it bred with a wild mosquito, only half their offspring would carry that genetic modification. A gene drive will make nearly all the offspring (close to 100%) will carry the Genetic Modification. The gene drive introduces a bias that changes the way genes are inherited.
So what exactly is a Gene Drive?
There are different kinds of gene drives including ones that occur in nature, for example a bacteria that can infect mosquitos, called Wolbachia, that leaves them infertile. This is being applied to try and control dengue, another mosquito borne disease, in Queensland.
Synthetic gene drives use CRISPR/Cas9 technology to cut out specific target genes and replace them with a modified gene, using the cells own repair machinery to copy the modified gene.
Gene drives will only work in practice on:
- Sexually reproducing species;
- Rapidly reproducing species (insects/rodents/crops rather than slow growing trees or elephants!);
- Researchers have already successfully engineered CRISPR-based gene drives in mosquitoes, yeast and fruit flies.
How could gene drives be used?
- The extermination (or control) of mosquitoes that transmit malaria, dengue, and zika pathogens;
- eradicating invasive species such as the possum in New Zealand or European carp, cane toads or rabbits in Australia;
- To control agricultural pests like fruit fly.
As with any potentially powerful technique, there are risks of unintended consequences, e.g., a gene drive targeted to a local population could spread across an entire species. Wiping out a species might have wider ecological impacts.
Why is controlling mosquitos important?
- Mosquitoes are one of the deadliest animals in the world.
- According to the World Malaria Report 2018, there were 435 000 malaria deaths, 61% of which were children under 5.
- The worldwide incidence of dengue has risen 30-fold in the past 30 years, and more countries are reporting their first outbreaks of the disease.
- Zika, dengue, chikungunya, and yellow fever are all transmitted to humans by the Aedes aegypti More than half of the world’s population live in areas where this mosquito species is present.