TBE – overview of disease occurrence 2025
TBE – overview of disease occurrence 2025
Since November 2023, TBE has been laboratory-notifiable to Statens Serum Institut (SSI), which reports annually on the occurrence of TBE detected in Denmark. This annual report covers the year 2025. Tick-borne encephalitis (TBE), also known as Central European encephalitis, is a viral infection transmitted to humans through tick bites. The disease may cause influenza-like symptoms and, in some cases, develop into encephalitis, particularly in adults/elderly persons.
For more detailed information on routes of transmission and trends in occurrence, please refer to the TBE – overview of disease occurrence in 2024. TBE reports from previous years can be found here.
The 2025 annual report shows a decrease in the number of detected TBE cases compared with 2024. Transmission remains limited to known and possible risk areas, and there are no signs of significant geographical spread in 2025.
TBE surveillance and areas of infection in 2025
In 2025, 10 cases of TBE were detected in Denmark (Figure 1). This represents a clear decrease compared with 22 detected cases in 2024 and 28 cases in 2023, which was the year with the highest number of detected cases with infection acquired in Denmark to date.
Of the 10 cases, four persons had a presumed place of infection in Sweden (Table 1). The remaining six cases with presumed infection in Denmark were distributed across already designated risk areas on Bornholm and in North Zealand.
Two cases were registered on Bornholm, two cases in Tokkekøb Hegn in Allerød Municipality, and one case in Gribskov Municipality – areas where TBE transmission has previously been detected.
Fredensborg Municipality has previously – like other forest areas in North Zealand – been designated as a possible risk area. In 2025, a case with presumed infection in Danstrup Hegn in Fredensborg was registered for the first time.
Figure 2 shows the number of TBE cases by municipality, accumulated for the period 2013–2024. Halsnæs Municipality and Bornholm Municipality continue to have the highest total number of cases during the period. Of the 10 cases of TBE detected at Statens Serum Institut in 2025, seven developed a typical biphasic course of illness.
As shown in Figure 3, most patients had symptom onset in July 2025. As in 2024, the number of cases subsequently declined over late summer, before increasing slightly again in October, although the numbers are small.
Flagging activities in 2025
By dragging an approximately 1x1 meter large white flag across the forest floor (“flagging”), it is possible to attempt to catch ticks, which are then collected. The collected ticks can subsequently be tested for various tick-borne microorganisms, including TBE virus (TBEV). It is generally very difficult to identify the limited areas (microfoci) with TBEV-infected ticks, as these are typically the size of a handball court or smaller.
In 2024, TBEV was detected in ticks from a small area in Jonstrupvang in Hareskoven after two persons had been infected with TBE in the area. The area where TBEV-infected ticks were found in 2024 was flagged again three times in 2025, and TBEV was not detected in the total of 1,363 collected ticks. Flagging was also conducted in Tisvilde Hegn, where 396 ticks were collected. TBEV was not detected in these ticks either. Additionally, 30 ticks from Bornholm were collected and tested, none of which were found to contain TBEV. However, this does not necessarily mean that there is no longer a risk of infection in these areas.
Advice and prevention
The risk of tick bites can be minimized by covering as much skin as possible when spending time in nature, for example by wearing long trousers tucked into rubber boots and a long-sleeved shirt. In addition, some mosquito repellents may also have a preventive effect against tick bites.
It is important to remove a tick as soon as it is discovered, either with fingers, tweezers, or a special tick removal tool. It is not crucial whether the entire tick is removed.
Vaccination
A vaccine against TBE is available and may be considered if you live in or regularly stay in known or possible risk areas from spring to autumn and frequently spend time in forests or scrubland – or if you acquire ticks simply by walking on paths. The risk period in Denmark is normally from May through October, and vaccination consisting of a total of three doses should therefore be initiated before this period. The vast majority of citizens are not expected to need vaccination. Persons at particular risk may include hunters, forestry workers, orienteers, and berry/mushroom pickers. It is rare for children to develop TBE, which may be because they often experience only a mild infection that is not detected.