Berlin (dpa) - Exotic pathogens are increasingly spreading in Europe. French authorities have just reported two first Zika virus infections transmitted by mosquitoes in Europe.

In Germany, the news now came that in other hospital patients in Germany a transmitted by domestic mosquitoes West Nile virus infection was detected. Affected were two women ill in late summer in Berlin and Wittenberg (Saxony-Anhalt), said Jonas Schmidt-Chanasit from the Bernhard Nocht Institute for Tropical Medicine (BNITM) of the German Press Agency (dpa). In the vicinity of the first infected person from the Leipzig region, there are also other suspected cases, including in younger patients.

The large number of serious illnesses is terrifying, said Schmidt-Chanasit. "That's just the tip of the iceberg." Only about one percent of infections led to such severe neuroinvasive diseases. According to this, hundreds of other infections with a slight course of life were to be assumed which were not diagnosed. "The West Nile virus apparently affects far more people in Germany than previously thought."

In about 80 percent of cases, a West Nile virus infection runs without symptoms and is therefore not recognized. According to the Robert Koch Institute (RKI), mild, nonspecific symptoms such as fever or rash are present in just under 20 percent. These too often go unnoticed. Heavier and deadly processes usually affect older people with pre-existing conditions.

At the end of September, the BNITM and other institutes had announced that for the first time a West Nile virus infection in humans transmitted by mosquitoes in Germany was detected. In mid-August, a 70-year-old from the surrounding area of ​​Leipzig was ill with encephalitis, which has now recovered. Previously, except for the case of a veterinarian in Bavaria, who was infected in the study of a bird, the pathogen was detected only in rare cases in travel returns.

First evidence of the West Nile virus in Europe existed decades ago, major disease waves have only been registered for several years. In 2018, the European health authority ECDC recorded around 2,000 infections, especially in countries such as Italy, Greece, Romania, Hungary and Croatia, and around 180 people died. In several German regions, the original African origin has been detected in many birds and horses since 2018. In northern climes he came through migratory birds and mosquitoes.

Unlike the West Nile virus, Zika can not be transmitted domestically, but only by exotic Aedes mosquitoes, which include the Asian tiger mosquito (Aedes albopictus) and the main carrier, yellow fever mosquito (Aedes aegypti). Yellow fever mosquitoes exist so far only Europe on Madeira and east of the black sea. Tiger mosquitoes, on the other hand, have made a very successful move northwards.

"Italy now has tiger mosquitoes everywhere," explained Schmidt-Chanasit. In other countries, such as France, Greece and parts of Germany, the white-striped animals spread. Unlike domestic mosquitoes, they often use small water reservoirs in pots of flower pots, for example, and are especially widespread in the urban environment - in large cities such as Rome and Florence, for example.

The first recorded zika virus infections transmitted by tiger mosquitoes in Europe were in Hyères, in the department of Var, southern France. Both cases occurred in August in a short time interval, it was said by the authority ECDC. The very first cases are most likely not, as Schmidt-Chanasit said. "Mostly there are no symptoms and the infection remains unrecognized."

Serious consequences can occur if women become infected with Zika early in pregnancy. In infants it can then come to brain and skull malformations. From 2015, thousands of such cases occurred during a Zika epidemic in Brazil. "Actually, we would have expected proof in Europe at that time," explained Schmidt-Chanasit. There is currently a major outbreak in Cuba. The source of the virus transmitted in France is not yet known.

All cases of Zika fever in Germany, according to RKI data, involved travelers, except for a single known case of sexual transmission in 2016. The presence of tiger mosquitoes does not automatically increase the risk, explained Schmidt-Chanasit. A decisive factor is the temperature, because the viruses could only multiply well in the mosquitoes when it is hot. It's about temperatures that are seldom reached in summer, said Klaus Stark, RKI expert on tropical infections.

If a tiger mosquito hits an infected person, the ingested virus can multiply in the mosquito and be transmitted to more people if the insect dies again. Unlike the yellow fever mosquito, however, the tiger mosquito is currently not capable of causing large Zika outbreaks, according to Schmidt-Chanasit.

However, tiger mosquitoes not only transmit the Zika, but also the Dengue and the Chikungunya virus. Hotspots for possible outbreaks according to the Hamburg virologists are Italy, southern France and Greece. Dengue cases exist especially in the south of France and Greece sometimes again and again. "At Chikungunya we already had two major outbreaks in Italy."

This virus is probably also the most dangerous for Germany, said Schmidt-Chanasit. "It can multiply well in the mosquitoes even at moderate temperatures." The pathogen causes long-lasting joint complaints in the hand, which are often misjudged as a rheumatic disease.