04 February 2021

The Guardian: “People v mosquitos: what to do about our biggest killer”

While our counterattacks are reducing the number of casualties she perpetrates – malaria deaths in particular are declining rapidly – the mosquito remains the deadliest hunter of human beings on the planet.

Taking a broad range of estimates into account, since 2000, the average annual number of human deaths caused by the mosquito was around 2 million. Humans came in a distant second at 475,000, followed by snakes (50,000), dogs and sandflies (25,000 each), the tsetse fly, and the assassin or kissing bug (10,000 each). The fierce killers of lore and Hollywood celebrity were much further down our list. The crocodile was ranked 10th, with 1,000 annual deaths. Next on the list were hippos with 500, and elephants and lions with 100 fatalities each. The much-slandered shark and wolf shared 15th position, killing an average of 10 people per annum.

They are masters of evolutionary adaptation. Mosquitoes can evolve and adapt to their changing environments within a few generations. During the Blitz of 1940–41, for example, as German bombs rained down on London, isolated populations of Culex mosquitoes were confined to the air-raid tunnel shelters of the London Underground, along with the city’s resilient citizens. These trapped mosquitoes quickly adapted to feed on mice, rats and humans instead of birds, and are now a species distinct from their above-ground parental ancestors.

What should have taken thousands of years of evolution was accomplished in less than 100. In another 100 years, jokes Richard Jones, former president of the British Entomological and Natural History Society, there may be separate Circle line, Metropolitan line and Jubilee line mosquito species in the tunnels below London.

Timothy Winegard

Throughout human history, mosquitos have been a constant companion – and source of plagues and suffering. Despite recent technological advances, diseases spread by mosquito bites continue to cause large numbers of deaths each year, prompting people to invent new strategies to keep the insects at bay. My personal favorite: zapping them with autonomous laser beams!

Mosquitoes illustration
[Source Image: johnnylemonseed/iStock]

With the advent of gene editing technologies such as CRISPR, several projects started experimenting with new approaches to this unsolved problem. Some ideas involve modifying mosquitos themselves, either by rendering them incapable of carrying the malaria parasite, or by interrupting their reproductive cycle, leading to a rapid collapse of the population. Others tested a transgenic fungus, genetically enhanced to produce spider toxin, as a more targeted replacement for pesticides. In fact, last year marked the approval of the first large-scale release of genetically engineered mosquitoes in Florida Keys and Harris County, Texas. This is scheduled to happen sometime in 2021, so we are yet to see results or negative consequences.

As I mentioned before, I am generally skeptical of solutions based on genetic engineering, because I fear we don’t know enough about the effects on the species and the ecosystem. A disappearing mosquito population could be quickly replaced by new invasive species, for example the Asian Tiger mosquito, which is better at carrying illnesses like West Nile. The effects on animals feeding on mosquitos are largely unknown; they may be poisoned as well by ingesting mosquitos infected with the transgenic fungus mentioned above. Mosquitos may even evolve past our attempts to genetically control them, thanks to their fast life cycle.

A more promising solution may come from nature itself: last year, scientists have discovered a microbe that completely protects mosquitoes from being infected with malaria. If this microbe can be distributed among wild mosquito populations, it could effectively end malaria without any risky genetic manipulation.

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