By Ben
Coxworth
September 22, 2022
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Transmission:Zero scientist Prof. George Christophides,
with a cage of the genetically modified Anopheles gambiae mosquitoes
(Photo credit: Imperial College London)
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Ordinarily, malaria is spread when a female mosquito bites
someone who is already infected with the malaria-causing Plasmodium parasite.
That parasite is carried with the sucked-up blood into the insect's gut, where
it enters its next stage of development. Once it reaches that stage, it moves
to the mosquito's salivary glands, so it can infect the next person the
mosquito bites.
That said, according to scientists from the
Transmission:Zero project at Imperial College London, only about 10% of
parasite-carrying mosquitos live long enough for the parasite to reach the
infectious stage. With that fact in mind, the researchers have set about
slowing the growth of the parasite within the insect's gut, to the extent that
the mosquito will simply die of old age before the parasite gets to its
salivary glands.
In order to do so, the scientists genetically
modified Anopheles gambiae mosquitoes – the main malaria-spreading
variety – so that they produced two types of "antimicrobial peptide"
molecules every time they ingested a blood meal. Obtained from African clawed
frogs and honeybees, these molecules interfere with the parasite's energy
metabolism, impairing its development.
As an added bonus, they also shorten the mosquito's
lifespan, boosting the likelihood that the insect will die before the parasite
becomes infectious. Ordinarily, adult female mosquitoes live for about six
weeks.
In lab tests, the modified mosquitos were shown to be much
less successful than regular mosquitos at transmitting the malaria parasite.
The idea is that if released into the wild, the modified mosquitos would
crossbreed with the others, gradually spreading their parasite-unfriendly genes
throughout the population.
Unfortunately, however, their shorter lifespan would put
them at a distinct disadvantage in this regard – the process of natural
selection would quickly eliminate their unique trait from the gene pool. For
that reason, the scientists are looking at further modifying the mosquitos by
adding a "gene drive," which is a genetic component designed to
force the spread of modified genes in a population.
Plans call for the modified mosquitos to be field-tested at
a facility in Tanzania. In order to lower the risks of disrupting the
ecosystem, two types of mosquitoes will be tested separately – one with only
the parasite-stunting molecules, and one with only the gene drive. If neither appear
to be ecologically harmful, they could then be combined into one strain.
"For many years, we have been trying to no avail to
make mosquitoes that cannot be infected by the parasite or ones that can clear
all the parasites with their immune system," said postdoctoral researcher
Astrid Hoermann, co-author of a paper on the study. "Delaying the
parasite’s development inside the mosquito is a conceptual shift that has
opened many more opportunities to block malaria transmission from mosquitoes to
humans."
The paper was recently published in the journal Science
Advances.
Source: Imperial College London