Looking at genetic solutions to mosquito-borne disease
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
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
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
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.