Tiger mosquito brings tropical diseases to Europe: Chikungunya case near Germany

Just a few kilometers from the German border, a person in France has been infected with the Chikungunya virus. The pathogen is transmitted by certain mosquito species, primarily the Asian tiger mosquito. It causes Chikungunya fever, which is accompanied by flu-like symptoms such as high fever, headache, and body aches.

In the past, chikungunya cases were primarily detected in travelers who had previously been to tropical areas where the mosquito species is present. However, this is not the case with the infection reported in France. It is an "autochthonous" chikungunya infection, meaning it was acquired locally and not abroad. The infected person stayed exclusively south of Strasbourg in the communities of Lipsheim and Fegersheim, about six to seven kilometers from the German border, reports the Robert Koch Institute (RKI) .

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Local outbreaks of mosquito-borne tropical diseases such as chikungunya and dengue have been observed in southern Europe for some time, said Hendrik Wilking at a Science Media Center press conference on Tuesday. Climate change is helping mosquitoes spread to cooler, more northern regions. "What is worrying is that we have to expect outbreaks that are not travel-related in Germany as well," warned the deputy head of the Gastrointestinal Infections, Zoonoses, and Tropical Infections division at the Robert Koch Institute (RKI).

Populations of the Asian tiger mosquito are already present in Germany. They are concentrated primarily in southwest Germany, along the Upper Rhine. "It's comparatively warmest there in Germany, and the mosquito feels most comfortable there," said Helge Kampen, head of the Laboratory for Medical Entomology at the Institute of Infection Medicine at the Friedrich Loeffler Institute (FLI). In addition, many travelers pass through these regions on their way to or from southern Europe.

Asian tiger mosquitoes are unknowingly introduced into Germany primarily as millimeter-sized eggs, according to Kampen. Sometimes, however, adult female mosquitoes also nest in truck cabins, for example, and thus cross the German border unnoticed. "The Asian tiger mosquito has spread dramatically in Germany over the past ten years." The expert suspects that there is a high number of unreported cases—especially since this species of mosquito is not subject to mandatory reporting.

According to the Robert Koch Institute (RKI), 75 cases of chikungunya have been registered in Germany from April to June. 15 cases in April, 29 in May, and 31 in June. All acquired abroad, i.e., travel-associated. These case numbers are noteworthy because in previous years there were only two to five cases per month. Travel-associated chikungunya cases are therefore "on the rise sharply," Wilking summarized.

Most people infected with Chikungunya recover completely, often within a week. The virus is more dangerous for chronically ill people, pregnant women, and infants. Deaths are extremely rare.

For a long time, there was no vaccine against Chikungunya. Last year, the vaccine Ixchiq was approved in Germany, followed by the vaccine Vimkunya in February of this year.

Ixchiq is a live vaccine, meaning it contains small amounts of viable Chikungunya viruses. However, these viruses are weakened in the laboratory beforehand so that they cannot cause the disease themselves. Vimkunya is a killed vaccine containing laboratory-killed, non-viable Chikungunya viruses or components thereof that trigger an immune response.

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Both vaccines are approved for a single dose in Europe for children aged 12 and over. For Germany, the Standing Committee on Vaccination (Stiko) has issued a more differentiated vaccination recommendation: In principle, both vaccines should only be used for travel vaccination —that is, for people traveling to an area where a Chikungunya outbreak is known and who are at high risk of developing severe illness. Or for "occupationally induced vaccination" —that is, for people who may come into direct contact with Chikungunya viruses, such as laboratory workers.

According to Stiko recommendations, the Vimkunya vaccine can be used on all people aged 12 and older. The live vaccine Ixchiq, on the other hand, should only be administered to people aged 12 to 59.

This is due to isolated reports of severe side effects in older people that occurred in temporal connection with the vaccine. The European Medicines Agency (EMA) subsequently prohibited the use of the vaccine in people aged 65 and over. After a review, the agency has now lifted this restriction – however, it emphasizes that Ixchiq should only be used after a careful benefit-risk assessment.

Peter Kremsner could also envision at least the inactivated vaccine Vimkunya as a preventative measure for children under 12. He generally advocates for more investment in therapeutic research. "We don't have any good treatment options—none for dengue, none for chikungunya," said the director of the Institute for Tropical Medicine, Travel Medicine and Human Parasitology at the University Hospital of Tübingen. There is also still room for improvement in vaccines.

All three experts aren't yet ready to talk about a pathogen with pandemic potential. "We're still on a safe path," said FLI researcher Kampen. This also applies to the tiger mosquito populations in Germany. They are still largely local, and the sources of infection are still manageable. "But citizens should start thinking a bit about the issue." Mosquito protection begins in one's own garden.

For example, by eliminating mosquito breeding grounds. Watering cans, rain barrels, and other containers used to collect water should be emptied regularly, or better yet, covered. Alternatively, there's BTI ( Bacillus thuringiensis israelensis ), a larvicide—a treatment against the larval stages of mosquitoes—that can be added to water containers.

There is currently no legal obligation to control the Asian tiger mosquito – neither for private individuals nor for government agencies. This only applies when it can be proven that the insects transmit pathogens. "This isn't particularly helpful in practice," said Kampen. "If you notice that a population is building up somewhere, you should really be on the lookout for the mosquitoes as quickly as possible. Otherwise, you have the problem that the population density suddenly becomes very high. Then control becomes significantly more difficult and significantly more expensive."