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Looking at genetic solutions to mosquito-borne disease
12/03/2018

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For humans, the deadliest animal on the planet is the mosquito. In 2017, almost half a million people died of malaria alone, while others were infected with mosquito-borne diseases like Zika and Dengue fever.

As researchers look for ways to stop these diseases, they’re increasingly turning to genetic modification as a way to reduce or eradicate mosquito populations. Genetic engineering can create sterile mosquitoes, mosquitoes that produce non-viable offspring, and even mosquitoes unable to carry the Malaria virus.

Although genetic modification could be the best way to stop the spread of deadly mosquito-borne diseases, it is not without risk. That’s why research teams are generally cautious about releasing modified mosquitoes into wild populations. On the other hand, some believe that it’s unethical not to take advantage of a technology that could save hundreds of thousands of lives worldwide.

Mosquitoes and malaria

Mosquitoes are, unfortunately, the ideal carrier for human disease. They feed on blood, and transmit viruses as they do so. A single female can lay thousands of eggs in her lifetime, so their population numbers are in the trillions. Because there are so many of the insects and they breed so rapidly, they’re impossible to eradicate using traditional insecticides.

The Anopheles mosquito is responsible for most cases of malaria worldwide. Cases are concentrated in Africa because the mosquitoes there have a longer lifespan, which gives the malaria parasite time to develop within its host.

The disease starts single-cell malaria microorganisms pass from a mosquito to a human. From there, they reach the liver, ‘hide’ from the immune system, and multiply. When they reach a certain level, they burst out of the liver cells and attack red blood cells, which finally triggers an immune response – typically chills, headaches, and fever. If treated promptly, infected people can recover. If not, anaemia and respiratory distress can happen very quickly, leading to severe illness and death. Children under five, pregnant women, and elderly people are most susceptible to the disease.

Changing the carriers

Many cases of malaria can be prevented with anti-malarial medication and regular spraying of insecticides in homes. The problem is, access to medication, insecticides, and timely treatment in case of infection is lacking. That’s why so many people suffer and die as a result of the disease.

Reducing or eliminating the mosquito population would help everyone, even those with no access to healthcare or preventative medication. Scientists have been working on genetic solutions to the mosquito problem for decades, and have already created new breeds of mosquito that could be released into the wild.

One type of engineered mosquito is immune to the malaria virus, so it couldn’t pass it on to humans. Once released into the wild population, the modified insects would pass on the edited gene to their offspring, reducing transmission. One problem with this approach is the way genes are passed on – the edited gene would only be passed to around half the offspring.

Researchers have worked around this problem by forcing the edited gene to become dominant. This way, around 95% of the offspring would be immune to malaria. Scientists hope that the changes would kick in so quickly that malaria – or the mosquitos – wouldn’t have the chance to evolve. Of course, this approach could potentially be adapted to prevent diseases like dengue fever, zika, Lyme disease, and even plague.

Other options for disease prevention include creating sterile male mosquitoes and releasing them into the wild, reducing the population over time; engineering mosquitoes with offspring that won’t survive to adulthood; and adding a gene that’s fatal to female mosquitoes – the ones who bite – so female offspring die while males live to pass on the gene. These modifications are all designed to reduce the mosquito population drastically, reducing the spread of disease in turn.

Risks, concerns, and perceptions

Any deliberate human influence on nature comes with the risk of unintended consequences – think of settlers introducing ferrets to control rat populations, and unintentionally decimating native birds instead. Although there is a long history of people breeding animal species for specific purposes, we have never deliberately interfered on a genetic level before.

Although scientists working on genetically engineered mosquitoes are confident in their work, they’re also aware of the potential for negative consequences. If the genetic changes don’t spread as rapidly as projected, mosquitoes or the malaria parasite could have time to adapt, which could make the problem worse. For example, if modified mosquitoes became more aggressive, or the malaria parasite adapted to infect other species, malaria transmission could increase rather than decrease.

Other barriers include resistance to genetic solutions from outside the scientific community. Many people fear genetic engineering, and misunderstand how it works, which leads to pushback when modified mosquito releases are planned. For example, some people fear that mosquitoes bred to be sterile could pass sterility on to humans, not understanding that genes are not passed from species to species.

Genetic engineering is already here

Despite misperceptions and potential risks, it’s likely that controlled releases of engineered mosquitoes will happen soon – in fact, some limited trials have already taken place. As researchers test the technology and build trust with local populations, they should eventually be able to modify wild mosquito populations for the benefit of humans everywhere.

Although change always comes with the possibility of unforeseen consequences, in this case, doing nothing is hardly an option. Every day, thousands of human beings die as a result of mosquito-borne disease – surely, preventing suffering on such a huge scale is worth the risk.

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