Many mosquito species in Germany can hardly be distinguished from one another for laypersons. Does that annoying “tzz” come from a native mosquito or an Asian tiger mosquito? The difference can be significant – if the mosquito bites. Because the tiger mosquito can transmit a number of dangerous pathogens such as dengue and chikungunya viruses.
The Asian tiger mosquito comes from the tropics, but has been spreading massively in southern Europe and parts of Central Europe since the 1990s, according to the Friedrich-Löffler-Institut. Local propagation was first detected in Germany in 2014. There are now firmly established populations, says mosquito expert Doreen Werner from the Leibniz Center for Agricultural Landscape Research (ZALF). Mainly in Bavaria and Baden-Württemberg, but also in Hesse, Thuringia and Berlin.
So far, no case has become known in Germany in which a disease was transmitted through the bite of a tiger mosquito that lives here – but experts believe that it is only a matter of time due to climate change. In the south of France, for example, Zika infections from tiger mosquitoes native to the region have been reported several times. There have been proven dengue infections in Madeira, Croatia and France, for example. Chikungunya outbreaks have also occurred in the Mediterranean region.
The EU health authority ECDC recently warned of the increasing risk of mosquito-borne diseases. The Asian tiger mosquito is spreading further north and west in Europe. The number of affected regions in the European Economic Area (EEA) has almost tripled within ten years. Unlike native mosquitoes, the white-striped animals often use small water reservoirs, for example in the saucers of flowerpots, and are particularly common in urban areas – even in large cities like Berlin.
If a tiger mosquito bites an infected person, the viruses that have been absorbed can multiply in the insect and be transmitted to other people if the mosquito bites again. However, the decisive factor here is not just the presence of the mosquitoes: According to experts, Zika viruses, for example, need great heat in order to be able to multiply well in the mosquitoes, with temperatures that have rarely been reached in Germany so far. The dengue virus, on the other hand, can multiply well in mosquitoes even at moderate temperatures. The pathogen causes long-lasting joint problems, for example in the hand, which are often misjudged as a rheumatic disease.
In addition, exotic mosquitoes are not the only potential carriers of dangerous diseases in Germany: In 2019, the Robert Koch Institute (RKI) recorded infections with the West Nile virus, which originally came from Africa, in sick people in Germany for the first time, which indicated transmission by native mosquitoes went back. Because the pathogen can hibernate in mosquitoes in Germany, experts expect an increasing number of cases up to larger seasonal waves of disease. Such outbreaks have been occurring in southern and south-eastern European countries for years.
According to the RKI, 17 West Nile infections were detected in people in Germany last year, compared to 4 cases the year before. A West Nile virus infection is symptomless in 80 percent of cases and is therefore not recognized at all. According to the RKI, almost 20 percent have mild, non-specific symptoms such as fever or skin rash. These too often go unnoticed. More severe and fatal courses usually affect older people with previous illnesses. Only about one percent of infections lead to such severe neuroinvasive diseases. Since tests and thus reliable evidence are usually only given in such cases, if at all, an alarmingly high number of annual infections can be assumed for Germany.
So in the future, do we have to be afraid of every mosquito bite, maybe sleep under mosquito nets soon? “Basically having concerns about every mosquito bite is certainly exaggerated at the moment,” says tropical medicine specialist Tomas Jelinek. “It’s a serious disease, but you don’t have to expect a mass occurrence in Germany.” However, it is quite likely that there will also be smaller West Nile eruptions in this country in the future.
It is unclear when the first dengue infections transmitted by tiger mosquitoes living here will be noticed. Destroying existing insect populations is important, emphasizes Werner. She has been in charge of the so-called mosquito atlas since 2012 and examines mosquito finds from all over Germany. Citizens who find a mosquito can catch it, freeze it, and mail it to Werner and her team.
The northernmost place in Germany where a tiger mosquito has been found is Berlin. In autumn 2019, a first copy reached the institute by post from an allotment garden in the Treptow-Köpenick district. In the years that followed, the animals were also found there. “The mosquito has now adapted so well that it laughs about our winter,” says Werner.
This year, the scientist has not yet had a tiger mosquito in the mail. However, that is not surprising: the season does not start until the end of June or beginning of July and lasts until September or October, depending on the temperature. Do we have to get used to the occurrence of invasive mosquito species? “You will gain weight, it’s only a matter of time,” says Werner. Education and prevention are needed.
