Genetically Modified Mosquitoes Have Been Created that Are Malaria-resistant

A genetically modified (GM) strain of malaria-resistant mosquito has been created. It is much better able to survive than insects who carry disease. The idea behind this is to introduce these GM mosquitoes into the wild in the hope that they will take over. The GM mosquito carries a gene that prevents infection by the malaria parasite.

This work has been carried out out by a US team, the details of which appears in Proceedings of the National Academy of Sciences journal. The team stressed that their studies are still in the very early stages, and that it could be 10 years or more before GM insects are actually released into the wild.

According to co-author Dr Jason Rasgon, from Johns Hopkins University in Baltimore, Maryland, "What we did was a laboratory, proof-of-principle experiment; we're not anywhere close to releasing them into the wild right now".

The way the team of researchers has approached this is to exploit the fact that the health of infected mosquitoes is compromised by the malaria parasite that they spread. As a result, insects that cannot be invaded are likely to be in better health and do much better than the disease carrying mosquitoes.

The team carried out experiments of equal numbers of GM and ordinary "wild-type" mosquitoes, that allowed them to feed on malaria-infected mice. As they reproduced, the GM mosquitoes survived. After nine generations, 70% of the mosquitoes belonged to the malaria-resistant strain. The scientists also inserted the gene for green fluorescent protein (GFP) into the transgenic mosquitoes. This made their eyes glow green. This helped the scientists to count the transgenic and non-transgenic mosquitoes.
The lead author of this study Dr Mauro Marrelli and his fellow colleagues wrote in PNAS: "To our knowledge, no-one has previously reported a demonstration that transgenic mosquitoes can exhibit a fitness advantage over non-transgenics". The GM mosquitoes not only had a higher survival rate, but they also laid more eggs. But when both sets of insects were fed non-infected blood they competed equally well.

However, for resistant mosquitoes to be useful to mankind in the wild, they must survive better than non-resistant mosquitoes, even when they are not exposed to malaria. The researcher concluded: "The results have important implications for implementation of malaria control by means of genetic modification of mosquitoes." The researchers said that GM mosquitoes that interfered with the malaria parasite would make it more difficult for the organism to re-establish itself after it had been wiped out from a target area.

Malaria is spread by the parasite Plasmodium. The disease is endemic in parts of Asia, Africa and central and south America. The organism is passed onto humans through the bite of the Anopheles mosquito. Around the world, up to 300 million people contract malaria each year, which causes illness and death. 90% of malaria are found in sub-Saharan Africa, where on average, one child dies every 30 seconds.

Dr Rasgon said that one area the team still needed to look into further was the type of malaria being used in the experiments. The mice were infected with Plasmodium berghei, which is only specific to mice. He said there was a big difference between this parasite and the type of parasite that infects humans. The technique would have to be tried and tested in those organisms as well. He added: "I think it will be 10 to 20 years before transgenic mosquitoes are released into nature. It's very difficult to predict what will happen when we release these things.There is quite a lot of research that needs to be done, both in terms of genetics and the ecology of the mosquitoes; and also research to address all the social, ethical and legal issues associated with releasing transgenic organisms into the environment."

Professor Chris Curtis, from the London School of Hygiene and Tropical Medicine, UK, said that many other strategies would be needed to combat malaria effectively. So even if the GM mosquitoes were effective to begin with, there was always the possibility that the malaria parasite could mutate, and that could limit its success. He said: "There will obviously be strong selection pressure on the malaria parasite to do that; and that's a problem with anti-malaria drugs and insecticides. We have to keep working to produce new tricks to try to keep ahead of what the parasite will try to do," he told BBC News. He said his work in Tanzania had shown bed nets laced with insecticide were very effective in combating infections.

Further tests will help to determine whether Professor Curtis is right.The team admitted that their tests were not flawless and that this was just the early stages of a potentially life changing experiment, that could help millions of people who are infected with malaria each year around the world.

Source:

http://news.bbc.co.uk/1/hi/sci/tech/6468381.stm