Among these already feared insects, the potential presence of exotic species, favored by global warming, risks complicating things. Research shows that the famous tiger mosquito, originating from South-East Asia and vector of numerous diseases (dengue, Zika, chikungunya) is increasingly present in Belgium. According to Sciensano, at present this (sub)tropical tiger mosquito has already wintered in four locations in our country: Ath, Kessel-Lo, Wilrijk and Lebbeke. The Institute of Public Health therefore considers that they are established in these four places.
In 2023, the presence of this mosquito had been identified in twice as many places as in 2022, on exactly 25 sites (including 18 private gardens), both in Flanders and Wallonia. “In neighboring countries, we have been able to demonstrate that there was a real establishment of the mosquito. We must objectively fear that this will also happen to us,” considers Frédéric Francis, who mentions global warming, the cause of less harsh winters: “This is a major element which explains the long-term establishment of certain species of mosquitoes which were not present before. It is the minimum winter temperature which will make it possible to eliminate or not certain exotic species, whether or not they will be able to develop the following spring”.
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Accidental introduction
Furthermore, other species of exotic mosquitoes are also found in our territory. Thanks to Sciensano’s Memo + monitoring project, we know that the Korean forest mosquito (Aedes Koreicus) is now located in Maasmechelen (its “low population” “remains well localized”) while an Asian forest mosquito, the Japanese mosquito (Aedes Japonicus) for its part took up residence in Natoye. Aedes JaponicuIt was probably introduced accidentally through the international trade in used tires of a local company. From now on, the presence and wintering of this species is confirmed in our country, according to Sciensano. “It is clear that the population of this mosquito is increasing at this site. Its elimination is no longer possible, but it is important to raise awareness among citizens of the region about the elimination of potential mosquito breeding sites, in order to reduce possible nuisances and possibly the transmission of pathogens.”, estimated Sciensano experts in a report in 2023.
“Unlike the tiger mosquito, which has a high propagation capacity and is a confirmed virus vector,” the populations ofAedes japonicus are no longer monitored since 2022, “the budget being limited”. “On the one hand because their spread is much slower and limited and, on the other hand, because they are not confirmed vectors of viruses in the field, explains the head of the Memo + project Javiera Rebolledo, epidemiologist at Sciensano. This is why all efforts are instead focused on monitoring the tiger mosquito, because if it establishes itself in Belgium, it could be responsible for the local transmission of these viruses. It is therefore considered a threat to public health. It is notably the vector responsible for the dengue epidemic in France and Italy in recent years.”
For his part, Aedes japonicus does not present the same risk profile, explains the researcher. “There is concern, however, that this species could become a pest problem or be involved in the transmission of arboviruses such as West Nile virus. It has been experimentally demonstrated, in the laboratory, that it is capable of transmitting these viruses.”
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More painful sting
This mosquito Aedes Japonicus would have another particularity: “Its bites are more painful than those of native mosquitoes” according to the Walloon authorities and scientists from the Royal Museum for Central Africa who studied it.
The intensity of the bites can in fact vary depending on the species, explains Frédéric Francis. “You should know that the major point in terms of this itching is the injection of saliva from the mosquito in question. There may be a specific signature in terms of saliva composition, proteins or enzymes that will be more allergenic for some. In addition, when these mosquitoes also find themselves having several blood meals, there is contamination with the blood of the previous host which also explains this variability in the composition of the saliva. But the second part of these skin reactions is rather the individual reaction of the person who is stung.”
”Aedes japonicus bites are no more painful than those of other exotic or native mosquitoes. But since it is a fairly large mosquito, we sometimes feel them morenuance Javiera Rebolledo (Sciensano), who adds that “itThis species can be aggressive when looking for food and has an insistent biting behavior especially outside and sometimes inside houses.”
Same observation for the tiger mosquito: “It is well known for its nuisance capacity because it is very aggressive when looking for food.”
Hungry mosquitoes
Another nuisance effect: the “increased feeding behavior” of these exotic mosquitoes, notes Frédéric Francis: if our native species are used to feeding mainly in the evening or at night, exotic species, like the tiger or Japanese mosquito for example, take their “blood meals” throughout the day (and not just at night or in the evening) and therefore bite continuously, which potentially increases the nuisance for their human victims.
In addition to these parameters, “It is currently the season of endemic forest mosquitoes. And, with rain, many floodwater mosquitoes are likely to hatch. People may react more to these species because they are less exposed to them compared to house mosquitoes to which exposure is more common”, explains Javiera Rebolledo. A reactivity of the body which results from antibodies which have not yet been produced by humans in reaction to the saliva injected by these mosquitoes intended to prevent the blood from clotting, explained recently to the Nieuwsblad Dutch entomologist Bart Knols.
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Several factors must come together for the outbreak of a disease
However, with regard to diseases potentially transmitted by mosquitoes, we must remember that several factors must be brought together, reassures entomologist Frédéric Francis (ULiège): “For us to truly have an explosion and dispersion of a viral disease, we must bring together the vector, the pathogen and the host who will be bitten at the same time and in the same place. So, as long as at a given moment, the tiger mosquito is present but there is no Source of virus, we are bitten, we have itching which can even be more severe, but we risk nothing in terms of illness. If we found ourselves in a very concrete way having people who go on vacation and who come back infected with Zika or dengue and are the Source of the pathogen in Belgium, while the mosquito is also present at the same time, this becomes problematic. It is also possible – this has been demonstrated in history – that we discover among the various European mosquitoes that some have a capacity to transmit diseases which are not present in Europe at the moment.
Furthermore, Sciensano does not expect the arrival in our country of other exotic species in the short or medium term. “Other invasive species, such as Aedes aegypti, are currently present in still very localized places, notably around the Black Sea (Turkey, Georgia, Russia) as well as in Madeira or Cyprus where a lot of efforts are being made to control and limit their spread.”
However, it is difficult to say whether certain species are already present here without being detected since there is currently no monitoring of all mosquitoes (exotic and native). “But a priori no”, estimates Sciensano epidemiologist Javiera Rebolledo.
