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Rise in Tick-Borne Encephalitis in Finland as Harmful Tick Species Spread Northwards

Tuesday 9th 2024 on 11:40 in  
Finland

Harmful tick species, namely the common tick and the taiga tick, have increasingly spread across wider areas in Finland, leading to a rise in serious tick-borne encephalitis infections. Over recent decades, ticks have moved hundreds of kilometers towards the north. They often reach the northernmost part of Finland via humans and livestock.

A growing population has been observed around Rovaniemi, where regular sightings are reported. The proliferation of ticks increases the risk of disease. After a long winter, the tick situation rapidly escalated in early summer. The frosty winter conditions with an insulating layer of snow were beneficial for the tick population, and the favorable situation has continued into the summer.

The taiga tick is particularly prevalent in the eastern region of Finland, Central Finland, Pirkanmaa, and along the western coast up to the Gulf of Bothnia. The common tick is abundant in coastal areas as well as in the same regions of inland Finland as the taiga tick.

Over the past 50 years, ticks have migrated 400 kilometers north on the west coast, and the boundary of their distribution area in Eastern Finland has moved 100 kilometers north. The length of the northern winter shortens the active season of ticks. Therefore, increasing tick populations are unable to thrive much further north of Rovaniemi, although sightings have been reported as far north as Inari.

The active season of the taiga tick typically quietens down in early July, but the common tick can remain active until October or November. When ticks thrive, the risk of disease also increases. For instance, there have been nearly ten cases this summer in the Oulu region that required hospitalization due to tick-borne encephalitis.

This summer, five confirmed cases of tick-borne encephalitis were reported in Sea Lapland. However, not all ticks carry the virus. The TBE virus occurs locally in nature. The presence of ticks does not mean the presence of the TBE virus. The virus may only be in one place or a few, circulating among rodents. On the other hand, ticks carry a lot of borrelia. In some places, even half of them carry the borrelia bacteria.

According to the Finnish Institute for Health and Welfare’s infectious disease register, there have been two cases of tick-borne encephalitis in Ostrobothnia this year, but none in South Ostrobothnia and Central Ostrobothnia. The borreliosis situation in these provinces is calm according to interviewed doctors.

The areas at high risk from ticks are reviewed annually. Free vaccinations against tick-borne encephalitis are given to people who live permanently or have long-term holiday homes in high-risk areas. However, the recommendation to get vaccinated is broader and extends to areas outside the national vaccination program. Changes to areas are made by examining the incidence of tick-borne encephalitis at both municipal boundaries and, if necessary, by postal code areas.

If there are more than 15 cases per 100,000 inhabitants per year, vaccination is recommended for all who stay in the area for a longer period. If there are 1-5 cases, changes are considered on a case-by-case basis. Changes to vaccination recommendations are assessed annually after the turn of September-October. This brings forward the start of the three-vaccine series to the beginning of the year. The recommendation is to take the first two vaccines when there is still snow on the ground.