2023-07-20 04:42:01
Par Guillaume Laurens
Published on 20 Jul 23 at 6:42 See my news Follow Actu Toulouse Altopictus teams, responsible for mosquito control in the event of arboviruses (dengue fever, in particular), have already carried out four times more insecticide treatments this year in Haute-Garonne … (©Altopictus)
It is the scourge of summer, in the agglomeration of Toulouse. With their tiny size, inversely proportional to the itching they cause, their discreet wing beats and their sneaky buzzing, they punctuate the conversations of the (last) aperitifs on the terrace: tiger mosquitoes abound in this summer of 2023 around the Pink City , where they find all the ingredients to grow as desired.
Two to five times more mosquitoes in Occitania
The tiger mosquito? Altopictus knows a ray of it. This company, which has an antenna at Low wall (Haute-Garonne), is entrusted by the Regional Health Agency with vector control operations – in particular curative – throughout Occitania, once morest the insect inevitably the most hated by the inhabitants.
The medical entomologist Guillaume Lacourits scientific manager, makes no secret of it: “Overall, we are in a summer with good vector abundance”.
In other words, it’s not just an impression: tiger mosquitoes are infesting the region more than ever. “In some municipalities in Occitania, there is an abundance two to five times higher to those observed in recent years.
Three times more eggs this summer in the Toulouse agglomeration
Close to the regional capital, “we have a surveillance network of fifty nest traps which are placed mainly around health establishments and a reinforced network around Toulouse-Blagnac airport”, develops Renaud Chevaliertechnical manager at Altopictus in Haute-Garonne.
“These traps allow us to have an estimate of the density female mosquitoes in the area” (those that bite, editor’s note).
For our monthly survey in June, we observed higher egg densities on certain traps than in previous years.
Renaud ChevalierTechnical Manager at Altopictus in Haute-Garonne
“In June 2023, on our networks of laying traps dedicated to monitoring, we observed an abundance in eggsAedes albopictus multiplied by three in the agglomeration of Toulouse, compared to June 2022”, corroborates Guillaume Lacour, adding that there is “variability depending on the place”.
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Twice as many imported cases of tropical diseases
THE arboviruses, these mosquito-borne viral diseases (notably the trio dengue, zika et chikungunya) are also on the rise around Toulouse, where the figures have doubled… while the “boom” of infections is often at the end of the summer, with the return from vacation in the infested areas, for many the departments of ‘Overseas.
As of Monday July 17, according to Renaud Chevalier, “concerning the imported cases of arbovirosis, we have had six since the start of the season (May 1), mainly located in Toulouse Métropole. Compared to the same date last year, we had only three cases”.
And four times more insecticide treatments
Third telling indicator: that of the “emergency health response” that Altopictus is in charge of providing, when cases of arbovirosis are confirmed. These are the famous insecticide treatments: “We have made eight so far, compared to two at this time last year”, lists Renaud Chevalier.
In the end, Haute-Garonne represents almost half of the activity identified throughout the region : “Since May 1 in Occitania, 13 imported and reported cases have given rise to 25 investigations and 20 treatments”, notes the scientific manager.
Three days to do it all
“On the dengue, chikungunya, or zika viruses, the three main arboviruses, once the disease is installed, we intervene to spray a insecticide adulticide », explains the medical entomologist. He details the well-oiled procedure:
We intervene at night, always following having warned the inhabitants of the district. We spray from the street with a pick-up, and when more precise work is needed, especially on the gardens, we come back to spray on foot from the street.
Guillaume LacourMedical entomologist, scientific manager of Altopictus
When cases of illness are confirmed, Altopictus teams spray from the street with a pick-up (©Altopictus)
“From the moment a case is reported to us, we have three days to investigate, inform local residents and proceed with the treatment”, supports Guillaume Lacour, who continues: “Wherever we are called upon to carry out interventions, we see this year that there is a strong increase in density of mosquitoes”. And for this specialist, the explanation for this resurgence is all found, it fell from the sky.
Rainy Spring Weather Makes Mosquito Happy
As the medical entomologist explains, if the tiger mosquito is feasting this year in Toulouse and in the agglomeration, “it’s linked to the climatology of summer 2023” and the heat + thunderstorm combo.
We have a relatively temperate season in Toulouse, marked by heat and numerous stormy episodes. Since March, it has been between +1 and +3°C compared to normal. However, the hotter it is, the more it will accelerate the development of the mosquito at the larval stage. At the same time, the conditions have been quite favorable to it: since March, between 50 and 130 mm of rain have fallen each month in Toulouse, knowing that the mosquito comes out of diapause, its hibernation, in March…
Guillaume Lacour
It should only get worse this summer…
In short, “between the hot spring, and the precipitation which kept water in the containers and other pots of all kinds”, this generated “a large quantity of larvae” in individuals, accompanied by “much less mortality at the larval level”.
We notice an explosion in the number of mosquitoes in Toulouse, as generally in Occitanie, where we see similar conditions, which are very favorable to its development.
Guillaume Lacour
In the end, the entomologist is a bit fatalistic for the rest of this season: “The upward trend in the number of cases (of arboviruses, editor’s note) observed will only get worse with increased circulation, but also with rising temperatures, because the hotter and faster it gets, the more virus there will be in the mosquito’s salivary glands”.
Moreover, little is known, but “40 to 70% of cases are asymptomatic, the virus is therefore not easy to detect”. And this can only, on arrival, promote its circulation.
“A year at risk” on the importation of viruses
“We are clearly in a year at risk in terms of virus importation”, further warns Guillaume Lacour: “There are a lot of epidemics [des arboviroses] in the world this year, with in particular an upsurge in dengue fever cases in the busiest areas by French tourists overseas, in Guadeloupe, Guyana, Martinique, and even on Reunion Island, when it is the southern winter”. We mechanically increase the probability of introducing the virus into mainland France”.
What do you give to the natives?
By domino effect, the health authorities are on the lookout for potential indigenous cases who might declare themselves on the territory, as was the case last fall in Haute-Garonne.
In these cases, the patient therefore did not go to the tropics, but was infested at home by a mosquito which had itself bitten an infected person, generally returning from a trip: “The virus is then transmitted from ‘man to mosquito, then from mosquito to man’, outlines the medical entomologist.
For now, according to health authorities, no indigenous cases of dengue fever was not counted this summer. But in 2022, Altopictus agents had been at work on two fireplaces in Haute-Garonne: the first in La Salvetat-Saint-Gilles with four people infected, the other in Toulouse in October with two others affected.
Each time, it was a case of dengue fever (serotype 3) and “our intervention made it possible to neutralize the circulation of the virus”, argues the scientific manager.
Did you know ? Dengue is also sexually transmitted
In addition to mosquito bites, you can also contract certain arboviruses during intimate relationships: “Sexual transmission of the virus is possible on dengue fever and zika”, observes Guillaume Lacour.
The city center of Toulouse rather spared, the outskirts very affected
Unsurprisingly, the colonies of tiger mosquitoes in Toulouse “are concentrated in the outlying districts, and in the other towns and villages of the agglomeration”, but they still relatively spare the city center:
Suburban residential sectors, in particular houses with gardens, are much more affected than the very mineral areas of downtown Toulouse.
Guillaume Lacour
If he delights in global warmingthe tiger mosquito therefore embodies the perfect antithesis of the necessary refreshment of the city: the more concrete there is, the fewer critters there are…
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