Scientists develop genetically-engineered mosquito that cannot pass on malaria



The mosquito is unable to carry malaria

Scientists have created a genetically modified mosquito which cannot pass malaria to humans.

The ultimate aim is replacing wild mosquitoes with the lab bred population - although scientists say this would take at least a decade to achieve

Malaria infects 250 million people a year and kills more than a million of them, mainly children.

The disease is caused by a parasite, a single cell organism called Plasmodium, but previous attempts to create GM mosquitoes have failed because although they reduced the insects' ability to pass on the pathogen, it was not eradicated all together.

But now a team of scientists believe they have created a mosquito immune to Plasmodium, meaning it cannot pass the disease on to humans.

Researcher Professor Michael Riehle, of the University of Arizona, said: 'It's not going to be a magic bullet or eradicate malaria, but it's a new tool in our tool chest.'



He said previous attempts to genetically alter mosquitoes had failed to make the insects completely immune to the the parasite.

He said: 'If you want to effectively stop the spreading of the malaria parasite, you need mosquitoes that are no less than 100 percent resistant to it. If a single parasite slips through and infects a human, the whole approach will be doomed to fail.'



So his team used molecular biology techniques to insert fresh genetic information into the mosquito's genome, then injected the genome into mosquitoes eggs.

The newly hatched insects, taken from a species that spreads malaria throughout the Indian subcontinent, carried the altered genetic information and passed it on to subsequent generations.

The researchers had targeted a piece of genetic code in the mosquito which acts as a metabolic switch which controls the enzyme Akt. Akt is involved in the mosquitoes growth, lifespan and immune system.

By genetically engineering this switch permanently to 'on', more Akt was produced, enabling the immune system to fight off Plasmodium.

It also shortened the lifespan of the mosquito.

Prof Riehle said: 'It was known that the Akt enzyme is involved in the mosquito's growth rate and immune response, among other things.

'So we went ahead with this genetic construct to see if we can ramp up Akt function and help the insects' immune system fight off the malaria parasite.'



When Riehle and his co-workers studied the genetically modified mosquitoes after feeding them malaria-infested blood, they noticed that the Plasmodium parasites did not infect a single study animal.

Riehle said: 'We were surprised how well this works.

'We were just hoping to see some effect on the mosquitoes' growth rate, lifespan or their susceptibility to the parasite, but it was great to see that our construct blocked the infection process completely.'



The shortened lifespan of the insect also helped the spread of the disease, he said, explaining: 'In the wild, a mosquito lives for an average of two weeks.

'Only the oldest mosquitoes are able to transmit the parasite. If we can reduce the lifespan of the mosquitoes, we can reduce the number of infections.'



The insects were kept in a highly secure lab to prevent them escaping, but the ultimate aim would be to see the GM mosquitoes replace those in the wild.

This could prove the hardest step of all, said Riehle, whose findings are published in journal Public Library of Science Pathogens.

He said: 'The eradication scenario requires three things: A gene that disrupts the development of the parasite inside the mosquito, a genetic technique to bring that gene into the mosquito genome and a mechanism that gives the modified mosquito an edge over the natural populations so they can displace them over time.

'The third requirement is going to be the most difficult of the three to realize.

'It would probably take at least a decade, if not more. The biggest thing we are missing is a mechanism for driving our genes through the whole population.'