Scientists have hailed the genetic modification of mosquitoes that could crash the insect’s populations as a “quantum leap' that will make a substantial and important contribution to eradicating malaria.
Previous efforts to tackle the disease, that kills more than 1 million people each year — most of whom are African children — have included bed nets to protect people and insecticides to kill the mosquito species most responsible for the transmission of malaria ( Anopheles gambiae ).
The new technique by a team at Imperial College London involves injecting mosquitoes with a gene that causes the vast majority of their offspring to be male, leading to an eventual dramatic decline in population within six generations as females disappear.
“You have a short-term benefit because males don’t bite humans [and transmit malaria],” said Andrea Crisanti, one of the authors of the new research, which was published in the journal Nature Communications on Tuesday.
“But in the long term you will eventually eradicate or substantially reduce mosquitoes. This could make a substantial contribution to eradicating malaria, combined with other tools such as insecticides.” The scientists injected mosquitoes with a gene from slime mould — a homing endonuclease called I-PpoI — which attached itself to their X chromosome during the male’s sperm-making process and effectively shredded part of the chromosome’s DNA. The result was that more than 95 per cent of the mosquitoes offspring were males. The researchers found that the modified mosquitoes mated with wild mosquitoes, creating fertile mosquitoes which then overwhelmingly produced male offspring, passing on the gene.
“Under field conditions the accumulation of X chromosome damage would significantly contribute to the demise of target populations,” the scientists say in their paper.
“The engineering is a quantum leap in terms of what has been done before,” said Crisanti, who worked on previous research in 2008, which took a similar approach but unintentionally resulted in sterile mosquitoes, meaning the gene’s ability to spread was limited. Imperial College London also published work in 2011 on a distinctly different approach to impair the fertility of mosquitoes generally, rather than distorting the makeup of their sex.
Distorting the sex of a pestNikolai Windbichler, a research fellow at Imperial College London and co-author, said that the concept of distorting the sex of a pest’s population is more than 50 years old but that the technology had not been available until now to execute the idea.
“The concept was suggested by Bill Hamilton [the famous evolutionary biologist, W.D. Hamilton], but until now there wasn’t a way to realise it. There are selfish chromosomes around but they’re too complicated, so we created something like this from scratch [the homing gene using synthetic biology], he said. “We found mosquitoes have a genetic achilles heel.” Dr. Luke Alphey, group leader of the vector-borne viral diseases programme at the Pirbright Institute, who was not involved in the research, described it as a “big step forward” and said field trials could be conducted after further testing.
“The overall goal of this research programme is even more ambitious — to develop a version of this genetic system that will spread itself through the target species, removing females and causing population crash or extinction as it goes,” he said.
Dr. Michael Bonsall, reader in zoology at the University of Oxford, described the research as “super cool work” and said: “This has important implications for limiting the spread of malaria.” Dr. Thomas Walker, lecturer at the London School of Hygiene & Tropical Medicine, said that the work was “very good science” and “very promising” but said any uncertainty was in how the GM mosquitoes would fare out of the lab and in the field.
“The biggest problem with releasing modified mosquitoes in to the wild, is will they compete with existing males? They need that mating between transgenic males and wild females. There is no evidence to think might not mate in the field, though maybe they will find males are not quite as fit [as wild male mosquitoes] on field release. But the theory is very, very good.” He added that because the researchers were attacking a multi-copy gene — rather than a single gene — the chance of wild mosquitoes evolving to resist the technique was limited.
Dr. Helen Williams, director of GeneWatch UK, a not-for-profit group that has been critical of previous GM mosquito research, warned of unintentional consequences of crashing mosquitoes’ populations. “We would want to ensure that the risks are properly considered before GM mosquitoes are released into the environment. For example, reducing the population of one mosquito species can increase the population of other mosquitoes, so you can potentially make it worse. If you change an ecosystem and remove a species, another species often moves into that niche.” She said the decision on whether they should be used in the wild should be down to the people living in the countries where the engineered mosquitoes would be released. — © Guardian Newspapers Limited, 2014
