The Zika epidemic, which threatens tens of thousands of unborn babies, has left more than just doctors thinking. While scientists are busy developing a vaccine against the "new Ebola", calls for the elimination of all mosquitoes that carry Zika and other dangerous diseases are louder. "Lenta.ru" tried to understand the genetic, radiological and chemical ways of implementing the "mosquito genocide" and its possible consequences.
The blood-sucking insects that infect humans with malaria and other deadly diseases have long and hopelessly damaged their reputation. According to some reports, mosquitoes have killed almost 50 percent of the historical population of humanity - more than wars, plague and famine. Malaria alone (transmitted by the bite of Anopheles mosquitoes) claims up to two million lives annually. South Asian Aedes albopictus, which actively populates all continents, spreads chikungunya, dengue, West Nile virus and other poorly understood dangerous diseases. The economic damage that mosquitoes inflict on humanity is staggering: dengue alone costs Brazil itself $ 1.35 billion annually.
It looks like the Zika epidemic could be the last straw. “Mosquitoes are flying syringes, as if specially“sharpened”to spread diseases. Zika is just the latest in their track record,”explains biologist Kevin M. Esvelt. Even the leading scientific journal Nature has argued that mosquitoes do not create any special benefits for the ecosystem and that their destruction will not bring any harm to nature.
And people only benefit.
Dry, heal, poison and irradiate
Until recently, it was mainly not about killing, but about controlling the number of insects. To do this, the nests of larvae are eliminated - freshwater reservoirs. During their short life, mosquitoes rarely fly beyond 180 meters from their birthplace. Eliminating water from bird feeders, old tires, flower pots, drainpipes, and the like can help reduce mosquitoes almost immediately. It was by draining marshes at the beginning of the 20th century that they fought against malaria in Cuba and Panama.
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But all the puddles, ponds, streams and rivers in the area cannot be dried, so chemical agents come to the rescue - insecticides and especially larvacids (drugs against larvae). Among the latter, Bacillus thuringiensis israelensis (Bti) is popular, a preparation based on bacteria that is toxic to mosquito larvae. Also, toxic traps are used to protect against pests: they mimic attractive "nests" and contain poisonous chemicals that kill larvae.
Mosquito larvae
However, these proven means from the point of view of radical mosquito repellents are very imperfect: they operate in a limited area, require constant human participation, and most importantly, they do not guarantee complete destruction. "Superweapon" against mosquitoes promises to create biotechnology.
The first approach is to infect mosquitoes with the harmful bacteria Wolbachia. The microbe not only shortens the life span of insects, but also makes them unable to carry diseases (such as dengue fever). Wolbachia wages its bacteriological war against other pathogens, suppressing them in the body of mosquitoes.
The trouble is that the artificially introduced Wolbachia to parasites kills them too early, and they do not have time to mate with females and spread bacteria throughout the population. But even if this problem is solved, Wolbachia infection is too expensive: it takes dozens of specialized laboratories and hundreds of employees to infect thousands of mosquitoes. According to scientists, this method bears fruit only in geographically isolated areas (such as the Galapagos Islands), where it can be guaranteed that after several months of expensive activities, healthy mosquitoes will not fly into the area.
Better known are the genetically modified mosquitoes raised by the British biotech company Oxitec: mutant males that transmit to local females a gene that causes insect larvae to die before they reach puberty. In 2009 in the Cayman Islands in the Caribbean, this technology reduced the population of Aedes aegypti by about 75 percent.
In 2015, Oxitec received carte blanche from the Brazilian authorities for experiments. In the neighborhoods of Piracicaba, where the highest concentration of Aedes aegypti mosquitoes (the vector of dengue fever) is observed, about six million genetically modified insects have been released. They not only contribute to the early death of their offspring, but also cause the larvae to glow red in ultraviolet light, which gives scientists the opportunity to monitor the effectiveness of this method. Biologists have placed pots of water in Piracicaba where Aedes aegypti females lay their eggs. The ratio of red to normal larvae showed that 50 percent of the offspring produced genetically modified mosquitoes.
Oxitec's GM mosquitoes are released into the wild in Brazil. January 2016
In a test conducted in the Brazilian city of Joiseiro, Oxitec insects reduced the local population by 95 percent in six months, nearly twice as effective as the most powerful insecticides.
However, scientists do not know how much the reduction in the number of vectors affects the incidence. “In theory, the fewer mosquitoes, the fewer people get infected, but in reality everything needs to be checked. Many insects can only produce a few new cases of the disease and vice versa,”says Margareth Capurro of the University of São Paulo, head of the Joiseiro trial. Other researchers warn that the effect of the new technology may be short-lived: mosquitoes from other areas will fly in, and the healthy part of the population will return to its previous size.
Genetic engineering tools are not limited to this. Geneticists at the Johns Hopkins Malaria Institute have developed genetically modified bacteria that live in the intestinal microflora of mosquitoes and give them inherited immunity to malaria pathogens. The University of Maryland has invented a transgenic fungus, reinforced with a substance from scorpion venom, which kills up to 98 percent of the malaria parasites in the mosquito.
Is it worth pushing evolution?
But all these promising methods, again, are not cheap and are limited in scale of impact, and the Zika epidemic is already taking on a massive character in South America (several million infected). The Achilles heel of GM mosquitoes is slow spread. Even Charles Darwin knew that evolution is in no hurry, and mutations are fixed in a population only under favorable environmental conditions. Unsurprisingly, costly mutants have to be made over and over again - even if the mutations are introduced by radiation, as the IAEA recently suggested.
A gene drive can "push" evolution - the artificial spread of a desired gene in a population by increasing its chances of inheritance (regardless of the benefits of the properties it encodes for the organism). Genes can be amplified (for example, those that remove X chromosomes in semen, which only produce male mosquitoes) using the human genome editing system CRISPR / Cas9. However, geneticists themselves call for caution in the use of CRISPR / Cas9 outside the laboratory: it is not yet known what consequences the alteration of the genome might have. So it is hardly possible to attract CRISPR / Cas9 to large-scale extermination of mosquitoes.
Loud calls to "kill mosquitoes" raise fears that South American authorities could panic, force their scientists to drop caution and begin genocide of mosquitoes. However, many researchers are convinced that human blood-sucking enemies are not at all useless for the ecosystem. They are an important food resource for freshwater fish, dragonflies, spiders, lizards, frogs and even birds. Removing mosquitoes from the food chain will hit not only these species, but also those who feed on them.
If someone is not worried about the future of Brazil's poisonous frogs or mosquito fish, mosquito fish, you can remind them that the extermination of mosquitoes in a particular area will free up a large ecological niche, which will be filled by mosquitoes from neighboring areas or other insects. According to entomologist Joe Conlon of the American Mosquito Control Association, "If we eradicate them tomorrow, ecosystems will shrink a little, and then return to normal, and the mosquitoes will be replaced by something better or worse." It is the “worst” that environmentalists fear. Hundreds of midges and ticks, flies and fleas will be happy to profit from thousands of liters of "ownerless" human blood - and who knows what diseases they will bring?
