Claire Bates / BBC News Magazine & Olivia Judson / The New York Times – 2016-02-02 19:42:47
Would it Be Wrong to Eradicate Mosquitoes?
Claire Bates / BBC News Magazine
LONDON (January 26, 2016) — The mosquito is the most dangerous animal in the world, carrying diseases that kill one million people a year. Now the Zika virus, which is carried by mosquitoes, has been linked with thousands of babies born with brain defects in South America. Should the insects be wiped out?
There are 3,500 known species of mosquito but most of those don’t bother humans at all, living off plant and fruit nectar.
It’s only the females from just 6% of species that draw blood from humans — to help them develop their eggs. Of these just half carry parasites that cause human diseases. But the impact of these 100 species is devastating.
“Half of the global population is at risk of a mosquito-borne disease,” says Frances Hawkes from the Natural Resources Institute at the University of Greenwich. “They have had an untold impact on human misery.”
More than a million people, mostly from poorer nations, die each year from mosquito-borne diseases including malaria, dengue fever and yellow fever.
Some mosquitoes also carry the Zika virus, which was first thought to cause only mild fever and rashes. However, scientists are now worried it can damage babies in the womb. The Zika virus has been linked with a spike in microcephaly — where babies are born with smaller heads — in Brazil.
There’s a constant effort to educate people to use treated nets and other tactics to avoid being bitten. But would it just be simpler to make an entire species of disease-carrying mosquito extinct?
Biologist Olivia Judson has supported “specicide” of 30 types of mosquito. She said doing this would save one million lives and only decrease the genetic diversity of the mosquito family by 1%. “We should consider the ultimate swatting,” she told the New York Times. [See story below — EAW.]
In Britain, scientists at Oxford University and the biotech firm Oxitec have genetically modified (GM) the males of Aedes aegypti — a mosquito species that carries both the Zika virus and dengue fever. These GM males carry a gene that stops their offspring developing properly. This second generation of mosquitoes then die before they can reproduce and become carriers of disease themselves.
About three million of these modified mosquitoes were released on to a site on the Cayman Islands between 2009 and 2010. Oxitec reported a 96% reduction in mosquitoes compared with nearby areas. A trial currently taking place on a site in Brazil has reduced the numbers by 92%.
So are there any downsides to removing mosquitoes? According to Phil Lounibos, an entomologist at Florida University, mosquito eradication “is fraught with undesirable side effects”.
He says mosquitoes, which mostly feed on plant nectar, are important pollinators. They are also a food source for birds and bats while their young — as larvae — are consumed by fish and frogs. This could have an effect further up and down the food chain.
However, some say that the role of mosquito species as food and pollinators would quickly be filled by other insects. “We’re not left with a wasteland every time a species vanishes,” Judson said.
But for Lounibos, the fact this niche would be filled by another insect is part of the problem. He warns that mosquitoes could be replaced by an insect “equally, or more, undesirable from a public health viewpoint”. Its replacement could even conceivably spread diseases further and faster than mosquitoes today.
Science writer David Quammen has argued that mosquitoes have limited the destructive impact of humanity on nature. “Mosquitoes make tropical rainforests, for humans, virtually uninhabitable,” he said.
Rainforests, home to a large share of our total plant and animal species, are under serious threat from man-made destruction. “Nothing has done more to delay this catastrophe over the past 10,000 years, than the mosquito,” Quammen said.
But destroying a species isn’t just a scientific issue, it’s also a philosophical one. There would be some who would say it is utterly unacceptable to deliberately wipe out a species that is a danger to humans when it is humans that are a danger to so many species.
“One argument against is that it would be morally wrong to remove an entire species,” says Jonathan Pugh, from Oxford University’s Uehiro Centre for Practical Ethics.
And yet that’s not an argument we apply to all species, says Pugh. “When we eradicated the Variola virus, which caused smallpox, we rightly celebrated.
“We need to ask ourselves, does it have any valuable capacities? For instance, is it sentient and therefore has the capacity to suffer pain? Scientists say mosquitoes don’t have an emotional response to pain like we do.
“Also do we have a good reason for getting rid of them? With mosquitoes, they are the main carriers for many diseases.”
The question is likely to remain hypothetical, whatever the level of concern over Zika, malaria and dengue. Despite the success of reducing mosquito numbers in smaller areas, many scientists say knocking out an entire species would be impossible.
“There’s no silver bullet,” says Hawkes. “Field trials using GM mosquitoes have been a moderate success but involved releasing millions of modified insects to cover just a small area.
“Getting every female mosquito to breed with sterile males in a large area would be very difficult. Instead we should be looking to combine this with other techniques.”
Innovative ways of tackling mosquitoes are being developed across the world. Scientists at Kew Gardens in London are developing a sensor that can detect each different species of mosquito from its distinctive wing beat. They plan to equip villagers in rural Indonesia with wearable acoustic detectors to track disease-bearing mosquitoes. This would help them manage future outbreaks.
Meanwhile, scientists at the London School of Hygiene & Tropical Medicine have worked out how female mosquitoes are attracted to certain body odours, raising hope for more effective repellents. Another promising avenue is to make mosquitoes resistant to the parasites that cause the diseases.
In Australia, the Eliminate Dengue programme is using naturally occurring bacteria to reduce the ability of mosquitoes to pass dengue between people.
“This is a more realistic approach for mitigating mosquito-borne disease,” says Lounibos.
Meanwhile, scientists in the US have bred a GM mosquito with a new gene in the laboratory that makes it resistant to the malaria parasite.
“We are playing an evolutionary game with mosquitoes,” says Hawkes. “Hopefully it’s one we can get on top of over the next 10 to 15 years.”
Aedes aegypti – spreads diseases including Zika, yellow fever and dengue fever; originated in Africa but is found in tropical and subtropical regions throughout the world
Aedes albopictus – spreads diseases including yellow fever and dengue fever and West Nile virus; originated in Southeast Asia but is now found in tropical and subtropical regions throughout the world
Anopheles gambiae – also known as the African malaria mosquito, the species is one of the most efficient transmitters for the spread of the disease
A Bug’s Death
Olivia Judson / The New York Times
LONDON (September 25, 2003) â€” Should we send the malaria mosquito the way of the dodo?
So far, genetic modification has been a tool of creation. We’ve made crops that grow faster or that are resistant to pests, we’ve made animals that produce useful hormones in their milk, we’ve even — presto! — made white rabbits that glow green under black light. But now another, more radical use for genetic modification is in the offing: the engineering of extinction.
The basic idea is simple. Specicide — the deliberate extinction of an entire species — could be engineered by exploiting the biology of selfish genetic elements. These are segments of genetic material found in the genomes of all organisms; they contribute nothing to the well-being of their hosts, but simply proliferate themselves. And proliferation is something they excel at.
A feature of all selfish genetic elements is that they cheat at Mendel’s rules of inheritance and so have better odds for getting into eggs and sperm than regular genes do. As a result, a selfish genetic element can spread through a population extremely fast — far faster than a regular gene — even if it is harmful to its host.
That is why these elements are attractive to genetic engineers: attach a useful gene to a selfish genetic element, release individuals modified to carry the element and, within about a dozen generations, that gene should be present in every individual in a population. Or, to engineer extinction, devise an extinction gene — a selfish genetic element that has a strongly detrimental effect.
The element could, for example, be designed to put itself into the middle of an essential gene and thereby render it useless, creating what geneticists call a ”knockout.” If the knockout is recessive (with one copy of it you’re alive and well, but with two you’re dead), it could spread through, and then extinguish, a species in fewer than 20 generations.
Whether this can work in practice remains to be seen. Designing an extinction gene won’t be easy. A suite of technical problems remains to be solved.
But the idea is moving from theory to experiment; suitable selfish genetic elements are starting to be engineered to attack the genes of laboratory fruit flies, the guinea pigs of the insect world. And although field trials remain far in the future, it is not too soon to ask ourselves whether we should even think about using such a potentially powerful technology to wipe out a creature.
Given how hard we try to prevent the demise of one species or another — from the African elephant to the northern hairy-nosed wombat — it may seem perverse to entertain the notion of causing an extinction on purpose.
Yet there’s a handful of species we’ve tried (and failed) to destroy — at great expense, both to the environment and to our wallets. Chief among these, and the most obvious candidate for specicide, is the Anopheles mosquito, the mosquito that spreads malaria.
Each year, malaria kills at least one million people and causes more than 300 million cases of acute illness. For children worldwide, it’s one of the leading causes of death. The economic burden is significant, too: malaria costs Africa more than $12 billion in lost growth every year. In the United States, hundreds of millions of dollars are spent every year on mosquito control.
What’s more, a malaria vaccine is still out of reach; the parasite’s resistance to drugs is a growing problem, as is the mosquito’s resistance to insecticide. The proposed extinction technology could eradicate the malaria mosquito, and malaria with it, within 10 years of the time mosquitoes modified to carry an extinction gene are released into the wild. Tempting stuff.
Or tempting fate? As with any new technology, the benefits of using it must be measured against possible risks. Here, the risks are two: ecological collapse and genetic escape.
Genetic escape is the idea that the extinction gene might somehow get into a species other than the target and inadvertently wipe it out as well. In principle, this could happen in either of two ways.
Anopheles mosquitoes might not be fussy about whom they mate with; if they engage in sex with mosquitoes of other species, the gene could spread into those species and eliminate them, too.
Most animals avoid sex with members of different species, so a priori, the likelihood of hybridization seems small; all the same, this is something that should be investigated experimentally before the technology is put in place.
Alternatively, the extinction gene itself might prove unstable, and jump into a different species entirely. Though such jumping is not unknown for wild selfish-genetic elements, it is rare, and the chance of this being a problem seems remote. (The risk to us from this technology is negligible. Even supposing an extinction gene appeared in humans — by accident or by malice — it would take thousands of years for extinction to be effected. During this time, it is inconceivable the gene’s spread would go unnoticed; once noticed, it could easily be stopped.)
What about the ecological impact of removing Anopheles mosquitoes? Hard to predict. But several facts are worth bearing in mind. First, our current methods of mosquito control are crude and kill more than just mosquitoes. An extinction gene at least has the benefit of being precise and clean. Second, there’s nothing sinister about extinction; species go extinct all the time.
The disappearance of a few species, while a pity, does not bring a whole ecosystem crashing down: we’re not left with a wasteland every time a species vanishes. Removing one species sometimes causes shifts in the populations of other species — but different need not mean worse.
Moreover, the earth is home to more than 2,500 species of mosquito. Even if we were to eradicate the approximately 30 species that are regular carriers of malaria, and for good measure, the Aedes mosquitoes that spread dengue and yellow fever, we’d hardly be creating a mosquito-free world. It is hard to argue that a targeted, genetic attempt to remove an insect that is clearly harmful to us is worse than the haphazard, expensive, destructive and largely unsuccessful approach we’re using now.
Nevertheless, friends of the mosquito will say that eradicating the mosquito is akin to shooting the messenger. Why not, they will surely ask, commit specicide on the malaria parasite instead? Alas, this is probably impossible to do by extinction gene: the parasite is prone to self-fertilizing, a habit that would prevent the gene’s spread.
Besides, to get the genetically modified parasite into the wild, you’d have to infect people with it, which would clearly be unethical. The obvious mosquito-saving alternative — modifying the creature so that it cannot spread the disease — is probably also unfeasible. This is technically harder than the extinction approach and there are, in any case, theoretical reasons to suppose the effort would fail.
Ideally, malaria would be defeated in other ways. Uganda has recently reported a 50 percent drop in death rates as a result of handing out free malaria medicines; if the program can be emulated and the trend sustained, perhaps by the time the technology is ready, it will no longer be needed. But if, by then, the situation is not much improved, we should consider the ultimate swatting.
Olivia Judson, an evolutionary biologist at Imperial College in London, is author of ‘Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex.’
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