Scientists have modified mosquitoes to produce sperm that will only create males, pioneering a fresh approach to eradicating malaria.
In a study published in the journal Nature Communications, 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.
“Malaria is debilitating and often fatal and we need to find new ways of tackling it,” said lead researcher Professor Andrea Crisanti. “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.”
In the first laboratory tests, the method created a fully fertile mosquito strain that produced 95 percent male offspring.
“What is most promising about our results is that they are self-sustaining,” said Dr. Nikolai Windbichler, also a lead researcher. “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.”
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, it 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 percent, 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 Organization, over 3.4 billion people are at risk from contracting malaria and an estimated 627,000 people die each year from the disease.
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 produce female offspring, while 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, almost all of the offspring of the genetically-modified mosquitoes were males.
“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,” said co-author Dr. Roberto Galizi. “Our goal is to enable people to live freely without the threat of this deadly disease.”
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