“The species was found in Portugal in 2017 for the first time. In the Algarve [in Loulé] and in Penafiel, we don't know if they happened coincidentally or not but there shouldn't be much difference, because they were still very localized foci at the time", José Manuel Grosso-Silva, curator of Entomology at the Museum of Natural History and Science of the University of Porto, told Lusa.

How it arrived in the Algarve is still unknown, but the introduction in Penafiel, in the district of Porto, seems to have taken place through a re-treading business, which imported tires with eggs of this mosquito deposited in the water that remained inside the tires.

“Mosquitoes have aquatic eggs, females lay eggs in water, and eggs develop in water. The tires, stored in piles, accumulate water inside and provide a place that, on the one hand, has water and bacteria and, therefore, food for mosquito larvae, and then has no predators”, explains the specialist.

The entomologist, with a doctorate from the Faculty of Sciences of the University of Porto, adds that there is still “no information on the widespread dissemination of the species from that point” where it was identified in Penafiel, clarifying that this “is neither a good nor a bad sign”, it just happens because “it hasn't been that long yet”.

Spreading across the country

Even so, he asserts that “it is more likely that the species will spread, as happened in Spain”, not least because, “either in the type of place where it was found in the Algarve, or in the tires in Penafiel, there are no predators”.

Therefore, “they are spreading, multiplying and expanding”, in the North region “much more easily, due to greater availability of water, and even due to climatic issues”.

As for the impact that the introduction of this mosquito has on ecosystems, Grosso-Silva says that “it is still not possible to give a definitive answer”, but “it is most certain that it causes discomfort and some kind of disturbance to the fauna, because they do not feed only on human blood, females bite different warm-blooded vertebrates, so it is very likely that they will also feed on several species.”

The Asian tiger mosquito arrived in Europe via Albania in 1979, and since then it has been detected in several countries, such as Italy, France or Spain.

Transmitting disease

It is capable of transmitting diseases such as dengue, zika and chikungunya, as well as filarial parasites, but “the health issue itself is not a problem, unless several conditions are combined”, emphasises the biologist.

“They are here, but the diseases they transmit are not here. They needed to find an infected person at the right time to bite and become carriers themselves. There has to be, inside the mosquito's body, the evolution of the parasite, and it will bite the next person in a position to transmit it. It is thus not a guaranteed thing that a mosquito that bites an infected person then transmits,” he details.

For “the transmission of the disease to be unavoidable” there must be “many mosquitoes and many people”.