2023-08-05 15:13:31
Although the tiger mosquito measures only a few millimeters, it has succeeded in spreading over most of mainland France in just 20 years. Global warming, which creates ideal conditions for its proliferation, increases the risk of disease spread more than ever. Politicians, scientists and health authorities are looking for solutions to this tiny parasite.
It is a feared pest, especially in summer. Absent until 2004 from French soil, the tiger mosquito is now well established in France. As of January 1, 2023, it had invaded 71 metropolitan departmentsplaced on red alert by the health authorities.
The spread of this black and white striped insect has become of great concern. It is a vector of diseases such as dengue fever, chikungunya or the Zika virus – viruses which have been the source of potentially fatal epidemics in countries such as Brazil or Reunion, where hundreds of thousands of people have been infected.
In France, concern has won over politicians. LFI deputy François Piquemal declared at the end of July that the spread of the tiger mosquito was a “political matter” and called on the government to take measures.
“Imported by neoliberal globalization […] and vector of serious diseases, it has an impact on our lives”, wrote François Piquemal in a tweet on July 24.
Yes the tiger mosquito is a political affair!
Imported by neoliberal globalization, settling on the destruction of our biodiversity, and a vector of serious diseases, it has an impact on our lives.
A #Toulouse and elsewhere we must act! https://t.co/ASiXJ67NY6
— Francois Piquemal (@FraPiquemal) July 24, 2023
Politicians, scientists and health authorities are racing against time to find solutions to stem the spread of mosquito-borne diseases.
Aedes albopictus around the world
Native to the forests of Southeast Asia, the tiger mosquito, also known as Aedes albopictus, made its first appearance on the European continent in 1979. After making the journey from China, the tiny insect has made its first stopover in Albania.
By laying their eggs in stagnant water present on the walls of man-made objects, such as used tires or containers, female mosquitoes have allowed their offspring to board ships carrying out transcontinental exchanges of goods. . The eggs, able to survive long periods of drought thanks to their waterproof shell, were able to cling for months. When the ships arrived at their destination, the eggs could hatch if the climate was warm and humid enough – which was the case in Albania.
“At the time, Albania was a communist state which maintained relations [commerciales] only with China,” explains Anna-Bella Failloux, a medical entomologist at the Pasteur Institute in France. “But the species never left Albania, because the country did not trade with the rest of Europe. This is proof that it is human activities that allow the spread of this mosquito.”
It took 11 years for the tiger mosquito to reach the rest of the continent, starting with the Italian port of Genoa. Once there, the species quickly spread and colonized all Italian provinces in just 10 years. Today, Italy is the most infested country in Europe by the tiger mosquito.
It was in 2004 that the first tiger mosquitoes were reported in France, more precisely in Menton, located just 11 kilometers from the Italian border. The mosquito then crossed the country on trains, trucks and even cars.
In France, its progression “has not been exponential”, specifies Pierre Tattevin, infectiologist and head of the infectious diseases department at the Rennes University Hospital, “but it has been continuous”. Since the arrival of the mosquito in France, “there are about four or five new departments concerned each year”, he indicates.
The tiger mosquito is a particularly resistant pest compared to other species. “In less than four decades, the tiger mosquito has conquered the tropical and subtropical world”, explains Anna-Bella Failloux. “For its cousin, Aedes aegypti, it took 400 years.”
Commonly known as the yellow fever mosquito, the Aedes aegypti can also transmit Zika, dengue and chikungunya. Unlike the tiger mosquito, it cannot establish itself in non-tropical regions.
female power
Of the 3,500 species of mosquitoes recorded in the world, only 15% bite humans. Among those that bite, “three are the main responsible for the spread of human disease”, according to National Geographic, including the tiger mosquito.
Female tiger mosquitoes are the only ones to bite, every five to seven days, but “they carry the virus until the end of their life”, explains Anna-Bella Failloux. Under ideal conditions, the species can live four to six weeks.
One of the peculiarities of the tiger mosquito is that the female can only be fertilized once in her life. “She has a spermatheca allowing her to store male sperm that she will use to fertilize her eggs throughout her life,” says Anna-Bella Failloux. These eggs can withstand drought “for months, even years” , explains the entomologist.
For infectious disease specialist Pierre Tattevin, tiger mosquitoes represent a “huge” threat to society. The dengue, Zika and chikungunya viruses are all “major public health problems in countries where there have been outbreaks, that’s what’s worrying,” he says.
These three viruses can cause similar symptoms, such as fever, headache, muscle and joint pain, rash, and nausea. For dengue, these symptoms disappear after one or two weeks, but in the most severe cases, the virus can be fatal.
In 2022, the French health authorities recorded 65 autochthonous cases of dengue, which means that the people who contracted the virus did so on the national territory, and not abroad. From May 1 to July 28, 2023, 227 cases of dengue have been identified in France.
A few days ago, two cases of dengue fever were detected in the Bouches-du-Rhône, the first autochthonous cases in the region in the year 2023. “To prevent the spread of the disease, mosquito control was carried out […] within a radius of 200 meters in the neighborhood where the cases reside (public road, private gardens), “said the Regional Health Agency. in a press release published on August 4, specifying that these people are cured today.
Zika, most often asymptomatic, can pose a serious threat to pregnant women, as it can cause birth defects in the child. Regarding chikungunya, some patients have reported long-lasting joint pain. Cases of death or serious symptoms are rare and usually related to pre-existing health conditions.
Global warming conducive to proliferation
According a study published in 2020 by the National Assemblyglobal warming facilitates the spread of the species, extending its period of activity and accelerating its development cycle.
“The tiger mosquito is much more efficient, active and comfortable at temperatures above 22 or 23 degrees”, recognizes Pierre Tattevin, who admits that global warming creates ideal conditions for the proliferation of the mosquito.
By conducting experiments to observe how climatic factors influence the invasion of the species, entomologists have found that when temperatures rise, mosquitoes perform better. “They fly longer and further, live longer, are faster and reproduce more quickly when the temperature exceeds 25 degrees”, relates Pierre Tattevin.
The experiments also showed that the tiger mosquito, unlike its cousin Aedes aegypti which thrives in tropical climates, could withstand colder temperatures for longer periods of time.
The ideal climatic conditions for the tiger mosquito in France are from May until September or October, but “when we arrive at the end of November and the temperatures drop below 10 degrees, the female will lay her eggs which will survive the winter season”, specifies Anna-Bella Failloux. “As soon as the temperatures rise in early spring, the eggs hatch and turn into adult mosquitoes,” she says.
Insecticide resistant
In order to limit the spread of the tiger mosquito at home, the National Agency for Food, Environmental and Occupational Health and Safety (ANSES) recommends emptying and turning over buckets, vases and other containers likely to contain stagnant water, covering cans with collecting water with mosquito nets and cleaning gutters to prevent mosquitoes from breeding. ANSES invites the public to wear long, loose and light-coloured clothing, and to use repellent products.
People residing in France can also report the presence of the tiger mosquito by using a dedicated platform set up by the agency, which explains that the tiger mosquito is very easy to identify. It is distinguished from a common mosquito thanks to its black and white stripes present on the body and on the legs which give it a very contrasting appearance.
???? Small, silent, daytime and striped: the tiger mosquito is spreading around the world.
The problem? It can transmit viruses such as dengue, chikugunya or zika to humans.
What to remember ????#CarefreeSummer pic.twitter.com/rxiPVYu6KK— Anses (@Anses_fr) July 12, 2023
For people who have traveled to a country where Zika, dengue fever or chikungunya exists, it is essential to monitor the symptoms, warns Pierre Tattevin. “If a person arrives in mainland France with one of these viruses, they must remain isolated so that they are not bitten by another mosquito which would contaminate those around them,” he explains.
Among the solutions that could be implemented on a national scale, some are more promising than others. Insecticide spraying is one, but Pierre Tattevin and Anna-Bella Failloux agree that it is far from ideal. The tiger mosquito has become acclimatized to insecticides and has even become resistant to them. This means that “larger doses are needed to kill them, which has a negative impact on our environment”, explains Anna-Bella Failloux.
Researchers are also studying the possibility of sterilizing male tiger mosquitoes to reduce their population. There sterile insect technique (TIS) consists in exposing the pupae of male mosquitoes (the stage before adulthood) to gamma rays which break down the DNA of their spermatozoa. Once released into the wild, the sterilized males mate with a female, but the eggs they lay are not viable.
A promising technique, the SIT has some drawbacks. “It is not easy to select and separate the male pupae”, explains Anna-Bella Failloux. “And the method requires having access to labs where you can breed mosquitoes, which is expensive to fund.”
The most effective solution so far has been to contaminate the males with the Wolbachia bacterium, which “makes it impossible for a virus to be transmitted by a mosquito, in particular that of dengue”, explains Anna-Bella Failloux.
According to World Mosquito Programmea trial of Aedes aegypti mosquitoes in Indonesia reduced dengue fever incidence by 77% and dengue hospitalizations by 86%.
“It’s a very promising solution,” says Anna-Bella Failloux, who believes that the only way to stop the spread of these diseases is to “kill the mosquito”.
This article has been translated from English. Find the original here.
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