Scientists from Imperial College London have tested a new
genetic method that distorts the sex ratio of Anopheles gambiae
mosquitoes, the main transmitters of the malaria parasite, so that
the female mosquitoes that bite and pass the disease to humans are
no longer produced.
In the first laboratory tests, the method created a fully
fertile mosquito strain that produced 95 per cent male
offspring.
The scientists introduced the genetically modified mosquitoes to
five caged wild-type mosquito populations. In four of the five
cages, this eliminated the entire population within six
generations, because of the lack of females. The hope is that if
this could be replicated in the wild, this would ultimately cause
the malaria-carrying mosquito population to crash.
This is the first time that scientists have been able to
manipulate the sex ratios of mosquito populations. The researchers
believe the work paves the way for a pioneering approach to
controlling malaria.
Since 2000, increased prevention and control measures have
reduced global malaria mortality rates by 42 per cent, but the
disease remains a prevalent killer especially in vulnerable
sub-Saharan African regions. Malaria control has also been
threatened by the spread of insecticide resistant mosquitoes and
malaria parasites resistant to drugs. According to latest estimates
by the World Health Organisation, over 3.4 billion people are at
risk from contracting malaria and an estimated 627,000 people die
each year from the disease.
Professor Andrea Crisanti from Imperial College London said:
"Malaria is debilitating and often fatal and we need to find new
ways of tackling it. We think our innovative approach is a huge
step forward. For the very first time, we have been able to inhibit
the production of female offspring in the laboratory and this
provides a new means to eliminate the disease."
Dr Nikolai Windbichler, also of Imperial, said: "What is most
promising about our results is that they are self-sustaining. Once
modified mosquitoes are introduced, males will start to produce
mainly sons, and their sons will do the same, so essentially the
mosquitoes carry out the work for us."
In this new experiment the scientists inserted a DNA cutting
enzyme called I-PpoI into Anopheles gambiae mosquitoes. In normal
reproduction, half of the sperm bear the X chromosome and will
produce female offspring, and the other half bear the Y chromosome
and produce male offspring.
The enzyme that the researchers used works by cutting the DNA of
the X chromosome during production of sperm, so that almost no
functioning sperm carry the female X chromosome. As a result the
offspring of the genetically modified mosquitoes was almost
exclusively male.
It took the researchers six years to produce an effective
variant of the enzyme.
"The research is still in its early days, but I am really
hopeful that this new approach could ultimately lead to a cheap and
effective way to eliminate malaria from entire regions. Our goal is
to enable people to live freely without the threat of this deadly
disease", concluded Dr Roberto Galizi, also from Imperial.
The paper, A synthetic sex ratio distortion system for the control of the
human malaria mosquito, is published in Nature
Communications.