[LONDON] A major stumbling block to using GM mosquitoes engineered to stop transmission of malaria may have been solved with a new genetic technique to ensure that they survive and propagate in natural environments.
The first genetically modified (GM) mosquito was produced in 2000 by scientists at Imperial College London, United Kingdom. Subsequent studies have shown that such modifications could be used to create mosquitoes with a reduced ability to transmit the deadly Plasmodium parasite responsible for malaria.
But finding a way to allow GM mosquitoes to thrive in wild populations has proven difficult. Without a suitable mechanism to ensure their survival, the mosquitoes would simply be out-competed by their native counterparts and die out, together with their disease-proof genes.
"Up to now — almost ten years later — no-one has really found out how to do that," Marcelo Jacobs-Lorena, a professor at the John Hopkins Malaria Institute, United States, told SciDev.Net last year.
Now, scientists at Imperial College have demonstrated a method to spread the beneficial genes through large populations, starting with just a small number of GM mosquitoes. The laboratory-based study was published in Nature yesterday (20 April).
The team bred Anopheles gambiae mosquitoes, the most important carriers of malaria, to contain a green fluorescence gene that makes them glow in the dark.
They then introduced the homing endonuclease gene (HEG) — which makes a copy of itself, ensuring all offspring end up with a copy of it as well — into around one per cent of the population.
The HEG gene, which is found in fungi, plants and bacteria, was designed to replace the glow-in-the-dark genes so that, if it spread through the population over time, less and less mosquitoes in each subsequent generation would glow in the dark.
The researchers found that in just 12 generations, the gene had spread through half of the population.
"We believe [that] in three to four years we will be able to apply this technique in native mosquito populations," Andrea Crisanti, lead researcher and a professor at Imperial College London, United Kingdom, told SciDev.Net.
Crisanti said the next step is to engineer the HEG to displace mosquito genes important for the transmission of malaria, as well as assessing the safety of the technique in human and animal populations.
The researchers plan to perform the first tests in two African countries, to be selected from a list of six that are being assessed at the moment.
"We need countries that not only have a serious malaria problem, but also clear safety and environmental legislation concerning GM organisms, and where we can work with a work with local team of scientists," said Crisanti.
Safety tests with larger populations of mosquitoes in more realistic environmental conditions will also take place, at the new EU INFRAVEC Mosquito Confined Release Facility, in Italy.
"This paper is a significant step forward," said Jacobs-Lorena. "For ten years we've known it is possible to engineer mosquitoes to make them poor transmitters of the disease, but we needed to give them some advantage over the native population. This research is a proof of principle demonstration in this direction."
Link to full paper in Nature
Nature doi:10.1038/nature09937 (2011)