Dangerous Asian mosquito invades Switzerland

A team of scientists at the University of Zurich discover the Asian rock pool mosquito, known to transmit the fatal West Nile virus, is established in five Swiss cantons. One of the team leaders, parasite expert Alexander Mathis, tells Swisster it is difficult to assess the likely health risks, but concerns about transmission of the disease might arise if infected tourists are bitten by the insect. A mosquito originating from Asia has established itself in parts of Switzerland bringing with it the threat of diseases such as the West Nile virus.

Scientists from the University of Zurich's institute of parasitology have found evidence of the Asian rock pool mosquito across an area of 1,400 square kilometres in five cantons, as well as in neighbouring Germany.

“It is the first time that an exotic mosquito has established itself in Central Europe,” parasite expert Alexander Mathis, one of the university directors of the research, told Swisster in a telephone interview.

The mosquito, known as Aedes japonicas, originally came from Japan, Korea and China. It has a history of spreading viruses after biting infected birds, mainly, but also horses and other mammals, including dogs, cats, domestic rabbits and squirrels.

The West Nile virus can in extreme cases cause encephalitis or meningitis. Although it has likely been around for hundreds of years, the disease was first isolated by scientists in Africa in the 1930s, where it was later found many residents had a natural immunity to the disease.

The virus was first identified in the United States in 1999. Eight years later, a total of 3,600 serious cases in humans were reported, leading to 124 deaths, according to the Centers for Disease Control and Prevention.

The risk of the mosquito transmitting serious disease in Switzerland is “difficult to assess,” Mathis aid. There is no evidence of any birds found in the country that have tested positive with West Nile virus, and no mammals either, he said.

But certainly the potential for propagation exists, he said, and scientists will be continuing to monitor the insect population.

One of the risks is that a tourist carrying the virus from a foreign country could be bitten by a rock pool mosquito, which could then spread the disease to another human, Mathis said.

The species, one of 3,500 varieties of the mosquito family, moved to North America and then to France and Belgium through the shipment of used tires, Mathis said.

Tires collect rainwater and serve as breeding grounds for mosquitoes, he said.

This particular kind of mosquito has been eradicated in France but still persists in Belgium, Mathis said. Researchers are not sure how it arrived in Switzerland, since the transport of used tires has been ruled out, he said.

Mathis said the mosquito has likely survived several winters in Switzerland, including the last one that was unusually cold. The scientist collaborated with Francis Schaffner, the University of Zurich’s mosquito expert to collect data on the insect.

The mosquito “is exotic but not tropical,” meaning that it can survive in cooler places and at elevations up to 1,500 metres above sea level, Mathis said.

Scientists have found evidence that the rock pool mosquito is established in at least 38 Swiss municipalities in the cantons of Zurich, Aargau, Lucerne, Solothurn and Basel-Landschaft.

The discovery of the rock pool mosquito follows concerns raised seven years ago over the appearance of the Asian tiger mosquito in Ticino. Another potential carrier of fatal viral diseases, the mosquito arrived from Italy, where it first appeared in the early 1990s, and was discovered north of the Alps for the first time in 2007 in the canton of Aargau.

These mosquitoes, named for the stripes on their legs and bodies, were held responsible for an outbreak of chikungunya fever in Italy in 2006. The fever afflicted 250 people and led to one death, but there is no reported evidence of the fever spreading to Switzerland.