The Asian tiger mosquito (Asiatische Tigermücke) was first detected in the Basel region in 2015. The Swiss Tropical and Public Health Institute has been monitoring the spread of this mosquito closely, as it is not only a nuisance, but can also transmit diseases. Despite numerous measures and broad-based information campaigns on how to stop the spread of these parasites, the tiger mosquito has taken over the entire canton of Basel-Stadt, and the canton has now developed a comprehensive action plan to be prepared for possible cases of dengue, chikungunya, or Zika that may be transmitted by the virus.

If a person becomes infected with a virus on a vacation abroad, returns home and is bitten by a tiger mosquito here, the mosquito can pick up the virus and infect other people. Such local (so-called autochthonous) transmissions in Europe have so far occurred primarily in countries such as France and Italy, with a local case of chikungunya occurring in Alsace, in early July 2025. No local transmissions have been detected in Switzerland so far, and in Basel-Stadt, the risk of local transmission is currently considered low. However, due to the established tiger mosquito population and the high level of travel among the Basel population, local transmissions cannot be ruled out. Therefore, the Department of Health is preparing for local transmissions and has developed an action plan, which provides precautionary measures, including raising awareness among healthcare professionals about symptoms and diagnosis related to tropical diseases like dengue, chikungunya, and Zika. It also regulates case management, including risk assessment in the event of an outbreak. In the event of a health threat, the cantonal medical officer will order control measures, which may include the spraying of insecticides.

Local Prevention Strategies

The risk of local disease transmission increases with increasing mosquito density. The core of the cantonal strategy is and remains the comprehensive control of potential breeding grounds for the Asian tiger mosquito. The most important and simplest measure in helping to contain the spread of the tiger mosquitos is by eliminating as much as possible areas of standing water, which can serve as a breeding ground for the mosquitos (this also helps against our pesky regular mosquitos!). They are suggesting that you try to make sure that there is no standing water by paying attention to the following in your gardens, balconies, or other outdoor areas:

• Remove the flat saucers underneath your flowerpots or empty them regularly.
• Cover rainwater collection barrels and make sure that no standing water collects on them.
• Store watering cans upside down.
• Dispose of your trash immediately and/or store it in a well-sealed container.
• If you have a kiddie pool for your young children, exchange the water weekly.

This fight continues throught the winter months to prevent the mosquito larvae from hatching in the spring, because the mosquitos and their eggs can survive the drought and the increasingly milder winters.  If you have a small pond or something similar, you don’t need to do anything because there are typically other organisms that will feed on the mosquitos or their eggs.

Prevention Abroad

The second important and simple measure to prevent illness is protection against mosquito bites when traveling to countries where diseases are transmitted by mosquitoes. People returning from a trip should continue to protect themselves against mosquito bites for 14 days after returning. This also applies to people who feel healthy, as many illnesses occur without symptoms. The mosquito can still transmit the virus when it bites. By taking good mosquito protection during and after a trip, the risk of disease transmission in Basel-Stadt can be reduced.

The better these two measures are implemented by the population, the lower the risk of local disease transmission and thus the likelihood that increased control measures such as spraying insecticides will be necessary.

You can find more information on the tiger mosquito on the cantonal laboratory’s website at www.kantonslabor.bs.ch/tigermuecke and https://www.bs.ch/themen/umwelt-und-bauen/tiere-und-pflanzen/invasive-tiere-und-pflanzen/tigermuecke.

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