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article imageRe-engineering mosquitoes to save millions of people per year

By Jeff Campagna     Apr 1, 2013 in Science
Mosquitoes have killed more humans than any other creature, war or plague in history, but now, scientists are making impressive headway in the fight against the disease-carrying insect.
They may be no more than an annoying buzz to people in North America and parts of Europe but mosquitoes pose a very serious threat of west-nile virus, eastern equine encephalitis, malaria and dengue fever transmission to two-thirds of the world's population. Dengue fever, which presently has no vaccine for infection prevention, infects between 50-100 million people yearly — for 25,000 of those people it will be fatal. A statistic that pales in comparison to the 655,000 people that die from malaria each year.
Currently, there are two popular methods for controlling mosquito populations. One method is larvicides, which are insecticides specifically targeted to kill insects during the larval life stage. The larvicides are injected into standing water like puddles, pools and bird baths where mosquitoes tend to lay their eggs. When looking at an urban or densely populated area, this process can prove to be quite challenging.
The second method, which is decidedly more straight-forward, is called adulticiding or fogging. Handheld machines that resemble leaf-blowers are used to dispense a low-volume insecticide solution that aims to kill the insects as they fly through the smoke. In India, biologists have begun mounting larger fogging machines onto the roofs of vans which are then driven through heavily effected-areas while discharging the fog. Because fogging releases insecticides into the atmosphere, this method of population control has some fairly obvious environmental and health concerns associated with it.
Scientists and biologists will tell you, however, that the best form of protection against mosquitoes is to wear a long sleeve shirt and a little bit of DEET — a sad prospect when one considers the incredible advances that have been made recently in the field of biological engineering.
"You would think that with all our science, with our advances in society, with better towns, better civilizations, better sanitation, wealth, that we would get better at controlling mosquitoes, and hence reduce this disease [dengue fever]. And that's not really the case," says English entrepreneur, Haydn Parry. Parry, who is the CEO of Oxitec, a bio-tech company devoted to innovative insect control, has some better ideas.
Parry has spent the last ten years dedicated to the search for a better solution to the mosquito problem — a solution that isn't dangerous to humans, one that has no lasting negative impact on the environment, one that is pervasive yet cost-effective for low-income areas and, most importantly, a solution that is species specific. He thinks he's found it.
There are two interesting biological features of the mosquito that Parry's team at Oxitec are trying to exploit. The first is that only female mosquitoes bite. The second is the fact that male mosquitoes are extremely adept at finding a female partner to mate with. The typical female mosquito will lay up to 100 eggs as many as five times during the span of her life.
If the male mosquito were to be carrying a gene which would cause the death of its offspring immediately after birth, the mosquito population would plummet hard and fast. The more modified male mosquitoes that are introduced into an environment, the more likely the females are to find a sterile mate. Parry's idea is brilliant in its simplicity. The Oxitec team has already performed field trials in lightly-populated villages in Cayman and Brazil and has seen encouraging results. In both cases, the mosquito population has plunged by almost 85 percent.
Andrea Crisanti, a parasitologist and microbiologist at Imperial College London, is also using re-engineering techniques to combat the threat of mosquito-borne disease. “We want to ask the mosquitoes to do what humans have not been able to,” says Crisanti, who has been experimenting with three different approaches.
One solution of Crisanti's is to engineer the insect so that it is unable to recognize the human scent. Another approach would be to significantly reduce the mosquito’s lifespan, thus reducing the amount of time it has to spread disease. The third solution, which Crisanti is most hopeful for, is to re-engineer mosquitoes in such a way that the females die in the embryonic stage, leaving the males to spread the modification until the resulting sex imbalance causes the population to crash.
Aside from the routine ethical concerns of 'playing God', scientists remain positive that the global eradication of mosquitoes won't cause any major environmental dilemmas. "If you pop one rivet out of an airplane's wing," says insect ecologist, Steven Juliano, of Illinois State University, "it's unlikely that the plane will cease to fly."
Entomologist Joe Conlon, from the American Mosquito Control Association located in Jacksonville, Florida, goes one step further by saying, "They don't occupy an unassailable niche in the environment. If we eradicated them tomorrow, the ecosystems where they are active will hiccup and then get on with life. Something better or worse would take over."
With the scientific community in agreement, there remain few hindrances beyond technical and biological advancements. For governments and organizations around the world, the process of re-engineering the world's mosquito population means logistical challenges and massive expenditures — but for millions of people in Africa, Southeast Asia, Australia and Central and South America, it means a longer life.
More about Science, Insects, Malaria, Dengue fever, Genetic engineering