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The European Center for Disease Prevention and Control (ECDC), the independent agency of the European Union that mainly deals with infectious diseases, has published data regarding the spread in 2023 of different types of mosquitoes and the diseases they transmit . As in the previous year, the spread of dengue and West Nile fever increased, two infectious diseases of tropical origin transmitted by mosquitoes which almost always cause minimal or mild symptoms, but can be risky for fragile people. The areas in which the tiger mosquito is widespread have also increased, a species native to Asia but now permanently widespread in southern Europe, responsible for the transmission of dengue and other diseases.
Invasive mosquitoes such as the tiger mosquito (whose scientific name is Aedes albopictus) arrived in Europe initially through international trade: their diffusion, however, was favored by certain land management practices but also by climate change. In several European regions today the hot season lasts longer and the days are hotter and more humid than a few years ago: these are all conditions that favor the spread of invasive mosquitoes.
As for dengue, a disease of tropical origin for which there are no specific treatments, but which is however only rarely serious or lethal, in 2023 there were 130 cases in the European Union: they have almost doubled since 2022, when there were 71 For the entire period from 2010 to 2021 in all the countries of the Union together with Iceland, Liechtenstein and Norway there were 73 cases.
Even “imported” cases, i.e. contracted in non-European countries by people who then returned to Europe, have increased: in 2023 there were more than 4,900, while in 2022 there were 1,572. The 2023 number of imported cases is the highest since records began at European level in 2008. In the first months of 2024, imported cases increased further in many European countries, which could lead to the 2024 numbers exceeding those of the previous year. This year in Italy there have been 197 cases of dengue, all imported, and there have been no deaths associated with the disease.
In 2023, 713 cases of West Nile fever were recorded in nine European Union countries, of which 332 in Italy. They are fewer than the 1,133 European cases in 2022 (which was the second year with the highest number of cases, after 2018), but they were recorded in a higher number of regions: 123, in 22 of which West Nile was registered for the first time.
Unlike dengue, almost all cases of West Nile fever are contracted directly in Europe. In most infected people, the disease causes no symptoms; only a fifth of those infected show any, usually mild. In rare cases the virus can cause convulsions, paralysis and coma, and in more serious cases, which generally concern elderly or debilitated people for other reasons, it can be lethal and it is best to prevent its spread also because, as for dengue, there is no specific cure .
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These data do not indicate that we should be alarmed by these viruses, but health authorities must still take into account the factors that favor the increase in risks and prevent them, for example with initiatives to control mosquito populations and with information. Among the methods that citizens can also use to limit the spread of mosquitoes is the removal of stagnant water from places such as gardens and saucers: mosquitoes in fact lay their eggs in humid places, such as the saucer of a plant .
Not all mosquito species can be vectors of diseases, that is, contribute to their transmission from person to person. Among the native European species, the common mosquito (Culex pipiens) can act as a vector for the West Nile fever virus, while the European species of the genus are known to Anopheles they can transmit malaria if widespread – Italy was declared malaria-free by the World Health Organization (WHO) in 1970 after several years with no cases. Instead, the main invasive species, the tiger mosquito, can act as a vector for the dengue virus, as well as for the chikungunya virus, which has similar characteristics to dengue, and the Zika virus, which can have more serious consequences.
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The tiger mosquito, recognizable by the visible white spots from which it takes its common name, has been present in Italy for more than thirty years: originally from eastern Asia, it spread due to the accidental transport of its eggs in used tires and plants ornamentals traded between different continents. The inside of a tire with a little water is an ideal place for the eggs of tiger mosquitoes, which can resist very different temperatures and in the absence of water even for months, and therefore in the hold of a ship for example.
The spread of the tiger mosquito in Europe: it is well present in the regions indicated in red, absent from those indicated in green, just introduced in those indicated in yellow (ECDC)
In some European countries the tiger mosquito does not yet exist, but it is slowly expanding its range, that is, the area in which it thrives: in the last ten years it has arrived in five new European countries. This is partly due to the increase in average temperatures but partly also to the mosquito’s ability to adapt to colder temperatures.
Then there are three other species of invasive mosquitoes that have established themselves in some European regions. Two have also arrived in Italy, where in fact they have been mentioned several times in the newspapers in recent years: the Japanese mosquito (Aedes japonicus) and the Korean mosquito (Aedes koreicus). Both can be confused with the tiger mosquito because they also have white spots; for the moment they are present in various areas of Northern Italy (the Korean one a little more than the Japanese one).
The Japanese mosquito is native to various East Asian countries and not just Japan. It also tolerates winter temperatures well in temperate regions and can survive in the absence of stagnant water, unlike the tiger mosquito. Thanks to these characteristics it has established itself in the United States and Central Europe, where it arrived in the 1990s thanks to international trade. It is known that it could in turn act as a vector for West Nile fever, dengue and chikungunya viruses.
The Korean mosquito, a little more present in Italy but less so in Europe than the Japanese one, has begun to spread more recently but in turn seems more capable of withstanding low temperatures than the tiger mosquito. In some areas of Russia it has transmitted a virus that causes encephalitis which, however, is not present in Europe. Like the other species of the genus Aedes it is also active during daylight hours.
The spread of the Korean mosquito in Europe (ECDC)
A mosquito species of most concern to ECDC is the so-called yellow fever mosquito (Aedes aegypti), which is native to Africa, has white spots and is considered the most dangerous for the transport of viruses; the disease from which it takes its name also has more serious symptoms than West Nile fever and dengue. The yellow fever mosquito has long expanded along the eastern coasts of the Black Sea, in some regions of Russia, Georgia and Turkey, and recently also in Cyprus – the eastern Mediterranean island which is also a member country of European Union.
For this as for the other species, the fact that it is present does not necessarily lead to the transmission of diseases and in particular the transmission of yellow fever, the virus of which is not present in Europe.
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