NEWS In the summer of 2024, a unique case of TBE infection was discovered in Västerbotten. A smaller study confirmed that there was virus in ticks on a limited part of Holmön island. Now the study is being expanded to investigate the occurrence of infection and virus in the county.
Ticks can carry the TBE virus.
ImageJens Rydell, Johnér bildbyrå ABIt is difficult to draw any major conclusions from the first study, as it is such a small data set
“It is very exciting and also important to find out the situation in Västerbotten”, says Anna Överby Wernstedt, professor at the Department of Clinical Microbiology at Umeå University.
In 2024, just under 400 cases of tick-borne encephalitis, TBE, were diagnosed in Sweden. In Västerbotten County, the disease is uncommon, 0–2 cases have been detected annually in the last ten years, and all are considered to have been infected in another county. The summer of 2024 was the first time that Region Västerbotten treated a person who was considered to have been infected in the county.
Anna Överby Wernstedt has TBE as her main area of research. Within a couple of weeks of the case in Västerbotten becoming known, she and her research team travelled to the island of Holmön just outside Umeå, where the person is suspected of having been bitten by a tick.
“We learned about the case in August and in September we were on the island to collect ticks to examine. We thought it was important to look more closely at this and we needed to do it as quickly as possible to be able to get hold of some ticks, as the ticks lie down and sleep”, she says.
The research team has conducted similar studies in southern Sweden, but not in Västerbotten County as there have been no cases before.
The current study was conducted in a small, limited area on Holmön. Analyses show that there was virus in the ticks, but at very low levels. The study will be expanded during the summer of 2025.
“It is difficult to draw any major conclusions from the first study, as it is such a small data set. In the new study, the collection of ticks will be expanded to more locations on Holmön, but also to other islands in Västerbotten County, such as Norrbyskär. We will also seek ethical permission to study whether people have been exposed”, says Anna Överby Wernstedt.
Most people who become infected with TBE do not have any symptoms at all, about a third get milder flu-like symptoms that go away within a week. However, some get more serious symptoms such as encephalitis with high fever, severe headache, confusion and possibly convulsions and paralysis.
“There are very mild strains in Germany that only cause diarrhea and no neurological problems, while there are strains in Russia that cause a mortality rate of 20 percent. The European variant has a mortality rate of 0.5 percent of those who are diagnosed. But only a fraction become ill and hospitalized”, says Anna Överby Wernstedt.
Through the study that is being conducted, the researchers can characterize the virus that the ticks in Västerbotten County carry. Results are expected in a year.
“By then we have collected ticks and analysed the samples that we have received, and hopefully blood samples from the people who move around on these islands. Then we can have a better picture of the situation”.
How should people act based on what we know today?
“At the moment we know very little. I cannot go out and say that everyone should get vaccinated when there has only been one case and we do not know if this strain is pathogenic and dangerous. We know too little, which is why we are doing this study”.
How did the virus come to Västerbotten County?
“We can only speculate. There is TBE in the Vasa region in Finland and it could have come with birds, that is the logical thing to assume, but we have no evidence right now. Humans are not affected by the spread of TBE, we usually say that humans are a dead-end host “,says Anna Överby Wernstedt.
