AMERICAN scientists are hoping to take the sting out of malaria with a strain of mutant mosquitoes genetically engineered to resist infection.
And if the technique transfers successfully from the laboratory to the field they say it could eventually stop the insects spreading malaria to humans.
The really clever thing is that when the mutant mozzies mate, their offspring inherit the same resistance to the disease. Professor David Conway, an expert from the London School of Hygiene & Tropical Medicine, was enthusiastic about the development. He said: “It’s not the finished product yet but it certainly looks promising. It does look like the genetic editing works.”
Other teams of scientists have been looking at genetically modifying mosquitoes to render them infertile, so that they die out. But some of their number fear that eliminating them entirely may have serious, unwanted consequences. Replacing the disease-carrying insects with harmless breeds is a potential acceptable alternative.
HOW DID THEY DO IT?
DR ANTHONY James and his team from the University of California used a gene editing technique called Crispr-Cas9, a molecular cut-and-paste that allowed them to snip out segments of the mozzies’ DNA and insert new ones.
On this occasion they inserted a new “resistance” gene into the insects’ DNA, which means – in theory at least – that if they bite humans they shouldn’t be able to pass on the parasite that causes malaria.
The team used a type of mosquito found in India – Anopheles stephensi – to carry out their experiments, in which the new DNA code rendered it a poor host for the malaria parasite.
The DNA programs for antibodies that fight the parasite, and was inherited by almost all the mosquitoes’ offspring across three generations.
Researchers hope the same method could work in other mosquito species and, while it would not be an overall solution to the malaria problem, it would be a useful weapon in the armoury against it.
WHAT EXACTLY IS MALARIA?
IT IS a nasty disease caused by a parasite called plasmodium, spread by a particular kind of mosquito that bites at night-time, and is a massive problem in countries across Asia, Africa and South America.
Almost half the world’s population – 3.2bn people – is at risk of malaria, which kills around 600,000 people a year, according to the World Health Organisation. This is despite the widespread use of drugs to treat infection, along with bed nets, insecticides and repellents to stop the mozzies biting.
It all starts when a female mosquito carrying the disease feeds on a human, biting into the skin and injecting plasmodium parasites into the bloodstream. From there they travel to the liver. The parasite then starts producing hundreds of thousands of harmful organisms called merozoites, which leave the liver and go back into the bloodstream. They then try to take over your blood cells, invading hundreds of thousands of them and infecting them with more parasites.
Then it gets really creepy – merozoites will start to change into sexual forms of the parasite which are primed to reproduce and circulate in the bloodstream. The next time a mosquito bites someone who has been infected, the disease is transferred through their blood, and the cycle starts all over again.
It has an incubation period of up to 18 days, after which people start to feel flu-like symptoms such as headaches, sweats, chills and vomiting. Muscle pains and diarrhoea can add to the unpleasant side effects. Sometimes victims will experience periodic fevers, with spells they feel very cold and then very hot in cycles of four to eight hours.
OUCH! BRING ON THE MUTANTS THEN?
NOT quite. The mutant, ninja, GM mozzies are being kept behind a series of locked doors in a high-security lab, purely because of what they are.
Science and society has long had a problem deciding when or how creatures whose DNA has been manipulated should be released into the wild, or what will happen to them once they are.
Biological engineer Feng Zhang led the first team of researchers using the Crispr-Cas9 technique on human cells.
“Gene editing is a little bit like geoengineering,” he said. “Once you go down that path, it may not be so reversible.” Far left, Anopheles stephensi. Top, a malaria victim; left, Professor David Conway and DrAnthony James Main picture: Reuters
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