As Covid crisis lingers, tiger mosquito boosts risk of tropical disease in France
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As the coronavirus epidemic evolves, French health officials and researchers are also monitoring the tiger mosquito, a potential vector for dangerous diseases that has spread worldwide – and has never been so active in France.
The tiger mosquito, which can spread tropical diseases including dengue fever, chikungunya and Zika, has found it easy to adapt to life in France since it arrived in 2004.
The French Health Ministry reports Aedes albopictus is “officially installed and active” in 58 departments this year, seven more than in 2019.
“It develops where other mosquitos are not present, specifically in the hearts of towns and cities: gardens, flowerpots and so on,” says Frédéric Simard, a medical entomologist at the French National Research Institute for Sustainable Development who hopes the coronavirus pandemic brings attention to risk factors for infectious diseases in general.
“There’s a lot of talk about Covid right now, but we should be wary of not seeing the forest for the trees,” he says. “Confinement has been an opportunity to reflect on how we relate to our environment.”
Outbreaks depend on density
Tiger mosquitos take their name from the distinctive white stripes on their black bodies. Averaging 5 millimetres in length, they are half the size as common mosquitos and harder to detect visually.
Originally from tropical and subtropical areas of Southeast Asia, they have spread to Europe, the Americas, the Caribbean, Africa and the Middle East since the 1960s.
Mainland France recorded its first locally transmitted cases of dengue fever in 2014, but the presence of mosquitos in itself does not necessarily mean diseases can – or will – spread.
“Mosquitos themselves do not carry viruses: they become infected by biting a person carrying the virus and then transmit it to someone else,” Simard says.
“The more mosquitos there are, and the more contact they have with humans, the more you increase the risk of transmission,” he continues. “It’s possible to have an R0 [zero reproduction or infection rate of contagious disease] with dengue or chikungunya that climbs to R3, which is comparable to Covid-19 before confinement.”
Human activities allow tiger mosquitos to spread and take root.
“When we build cities, we eliminate predators and competitors and create their ecological niche,” Simard says. “The more cities there are, the more places the mosquito will have to live.”
If mosquitos and viruses both thrive in warmer temperatures brought with climate change, Simard says the tiger mosquito migrates with the global flow of people and goods.
“The tiger mosquito is active and bites humans during the day,” Simard says. “It follows us into our cars, trucks and trains. Shipping goods within and between continents, in other words globalisation, has also perpetuated the spread.
“We spread it all over the planet by our means of transportation, and we give it a place to live with our buildings.”
Learning to live with the mosquito
Tiger mosquitos have become resistant to insecticide, and getting rid of them once they have a colonised a territory has proven virtually impossible.
Laboratories including France’s Pasteur Institute are testing whether they can sterilise mosquitos or render them incapable of transmitting viruses, but any solution is years away.
“It’s very likely that the mosquito will continue to spread as more environments become favourable to it around the world, not just in France,” Simard says. “People need to be aware of their responsibilities.”
One way is to limit standing water in which mosquitos reproduce, including rainwater that accumulates in cups and bowls. But the tiger mosquito also points to larger issues of how humans inhabit the planet.
“When we build structures for our comfort, if we’re not careful, we also favour the proliferation of mosquitos,” says Simard, adding the same applies to travel.
“Every year people go on vacation in tropical regions where viruses circulate and bring them to France. We now have a risk of local transmission via mosquitos that we’ve allowed to grow at home.”
For all humanity’s capacity to disrupt the natural world, eliminating mosquitos appears to be out of the question.
“We do it unintentionally to endangered species every day,” Simard says. “Mosquitos may be small, but they’re far from endangered.”
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