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'Gene drive' could halt malaria transmission

30 November 2015
Appeared in BioNews 830

Using 'gene drive' technology, scientists have created mosquitoes with malaria-resistant genes that could spread rapidly into wild mosquito populations, potentially wiping out the disease in some areas.

Researchers at the University of California, Irvine, used genome-editing on mosquito eggs to bypass standard patterns of inheritance, ensuring that all offspring inherited the resistance genes, rather than just half, as would normally be expected. In the lab, they were able to spread the malaria-resistance genes to 99.5 percent of mosquitoes.

'Strains based on this technology could have a major role in sustaining malaria control and elimination as part of the eradication agenda,' Professor Anthony James of the University of California, Irvine, told the Guardian.

Professor James's team had previously bred mosquitoes to carry a gene to make antibodies against the malaria parasite Plasmodium falciparum. But they had no way of transmitting the gene into a wild population since the gene could only be inherited 50 percent of the time.

But in January of this year researchers at the University of California, San Diego, demonstrated a way of using CRISPR/Cas9 technology to create a gene drive in fruit flies. The two teams then collaborated in this latest study on mosquitoes, which was published in PNAS.

Just as with humans, a mosquito larva inherits one chromosome each from its father and mother. The gene-drive technology ensures that the malaria-resistance gene gets copied over from one chromosome to the other once the egg is fertilised. They also added a tracer gene to give the offspring red fluorescent eyes so that the genetically modified offspring could be easily identified. 

The team worked with the Asian mosquito species Anopheles stephensi, which is responsible for a large proportion of malaria cases in the continent. Globally, there are around 200 million cases of malaria in and over 400,000 deaths each year.

The approach has its critics, who fear that the accidental release into the wild of gene drive organisms could lead to an irreversible ecological disaster. In August, a group of scientists wrote in Science, warning of the potential dangers of this new technology and calling for safety measures to be put in place.

Dr Simon Bullock, a geneticist at the MRC's Laboratory of Molecular Biology in Cambridge, was one of those who cautioned against the technology.

'Accidental or malicious release of a gene drive system into the wild could have unpredictable ecological consequences and thus researchers must use multiple safeguards that are robust to human error and nefarious actions,' he told the Guardian.

However, Dr Bullock said that California scientists had not mentioned any such safeguards in their PNAS paper. 'Given the highly sensitive nature of this technology and their call for transparency in this area of research, I'm flabbergasted that the authors have not disclosed in the publication detailed information on the containment procedures used in this study and how they were evaluated.'

Professor James said that while field tests could be ready within a year, he does not plan to carry them out any time soon. 'It's not going to go anywhere until the social science advances to the point where we can handle it,' he told Scientific American. 'We're not about to do anything foolish.'

SOURCES & REFERENCES
'Anti-malarial mosquitoes' created using controversial genetic technology
The Guardian |  23 November 2015
Gene drive method could rapidly halt malaria transmission
New Scientist |  25 November 2015
'Gene Drive' Mosquitoes Engineered to Fight Malaria
Scientific American |  24 November 2015
Highly efficient Cas9-mediated gene drive for population modification of the malaria vector mosquito Anopheles stephensi
PNAS |  23 November 2015
University of California scientists create malaria-blocking mosquitoes
University of California, Irvine (press release) |  23 November 2015
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