The West Nile mosquito (Culex modestus) has been confirmed in an area by the Klarälven river just north of Karlstad, according to Dagens Nyheter. The Swedish Veterinary Medical Institute (SVA) identified the mosquito using DNA analysis after it was captured last year by a company monitoring mosquitoes. This is the northernmost find of the species in Sweden, and SVA mosquito expert Anders Lindström stated that there are likely populations along the way, as mosquitoes do not fly long distances after hatching.
The mosquito has moved about 50 miles north in Sweden since it was first discovered in Skåne ten years ago. Dagens Nyheter reports that the first discovery was in 2016 in Simrishamn, and the mosquito was abundant around Falsterbo in 2017, subsequently spreading up the west coast. The latest reports before Karlstad were from Halmstad, and SVA has confirmed the mosquito has moved about 30 miles further north to the Klarälven area.
The West Nile mosquito is unusually aggressive and attacks humans even in wind and sun, according to Dagens Nyheter. Anders Lindström explained that it can spread virus between birds and humans, making it important to track. The mosquito can carry the virus that causes West Nile fever, which can lead to flu-like symptoms and, rarely, fatal brain or meningeal inflammation.
No infected birds have been found in Sweden yet, Dagens Nyheter reports. However, in Denmark, infected birds were found last year, and the infection has also been confirmed in several horses. Lindström noted that the virus is moving north in Europe and is also in Estonia, adding that it would surprise him if it does not appear in Sweden soon, possibly this year if the summer is warm.
Karlstad Municipality has investigated the occurrence of flood mosquitoes and methods to reduce problems when large numbers hatch after floods, according to the municipality. If permits are granted, biological mosquito control will be carried out from helicopters targeting larvae in water before they develop into flying mosquitoes. The method uses a biological control agent used in several places in Sweden where flood mosquitoes cause problems for humans. Municipal ecologist Sara Blad stated that an application was submitted to the Swedish Environmental Protection Agency last autumn for permission to control flood mosquitoes biologically, and a decision is expected within a few days.
Great. We have been wishing for this for several years.
The control agent has very little impact on humans and other animals, according to Karlstad Municipality. Sara Blad stated that there are no environmental risks at all with the spraying, as reported by SVT Värmland. The municipality plans an information meeting on April 15 at 18:00 at Skårekyrkan, and offers an SMS service for animal owners who may be disturbed by low-flying helicopters.
According to SVT Värmland, Madeleine Strandgård, a resident of Skåre, described the planned control as great, noting that residents have been wishing for it for several years. Sara Blad said there have been many complaints from Skåre about the mosquito situation.
The mosquito was captured last year by a company doing monitoring and biological control of mosquitoes, Dagens Nyheter reports. SVA confirmed it was a West Nile mosquito using DNA analysis.
The mosquito originates from warmer latitudes and has spread north in Europe, likely linked to climate change, according to Dagens Nyheter. This northward spread is consistent with observations in other European countries.
It remains unclear whether the Swedish Environmental Protection Agency will approve the application for biological mosquito control, and when the control would begin if approved. The specific areas along Klarälven that will be affected have not been detailed. Additionally, it is unknown whether the West Nile virus has been detected in mosquitoes or birds in the Karlstad area, and how the municipality's control efforts, which target flood mosquitoes, will impact the West Nile mosquito population.