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Tick-borne Encephalitis in Sweden

Recent reports highlight the fact that Sweden has the highest rate of Tick-borne encephalitis (TBE) in Scandinavia, exceding even those of Russia in 2008. [1,2]

The following background data on TBE in Sweden are abstracted from Gideon. Primary references are available on request.

Time and Place:
Disease rates peak during July to August.
– Natural foci are found throughout the southern and middle parts of Sweden up to the counties of Varmland and Dalarna and further north along the Baltic sea.
– Cases are identified on the Stockholm archipelago, the middle and eastern parts of lake Malaren close to Stockholm, the coastal area of the Baltic sea from Stockholm further south to the city of Kalmar and the islands of Oland and Gotland.
– Highest incidence is found on the East Coast, (particularly on the Stockholm archipelago), the eastern region of Lake Malaren and the Gotland Island region.
– The first cases in Skane were reported in 2001. Six cases were reported in the region to 2006.
– 65.3% of cases reported during 1992 to 1996 were acquired in Stockholm, 15.2% in Sodermanland, 6% from Ostergotland or Gotland, and 4.9% from other countries (primarily Finland).
– 402 cases of TBE were registered during 1955 to 1993, with a case/fatality rate of 0.5%. During this period, the disease rate in Stockholm County was 3.4 per 100,000 per year.
– 71% of cases in 2001 were reported from Stockholm, Uppsala and Sodermanland.
– 56% of cases in 2003 were from Stockholm, 15% from Sodermanland and 6% from Uppsala.
– In 2007, TBE virus was the most common agent of viral meningitis in Sweden, accounting for 37.4% of cases.

The male/female ratio among TBE patients is is 2.1/1; and the median patient age is 41.5 years.

Exported cases:
Tick-borne encephalitis was documented in a Swedish national in England (1991 publication).
An American traveler acquired Tick-borne encephalitis in Sweden in 2006.

Prevalence surveys:
21% of adult aseptic meningitis in Northern Stockholm (1999 and 2004)

Seroprevalence surveys:
4% to 22% in endemic areas, and 5% Stockholm
3.5% on the island of Asp (Southeast Sweden) in 1991; 12% in 2002
0.8% of persons in northeastern Skane are seropositive.

Tick-borne encephalitis virus has been identified in Ixodes ricinus found on migrating passerine birds.


1. Berger SA. Infectious Diseases of Sweden, 2010, 417 pp. Gideon e-book series

2. Berger SA. Tick-borne Encephalitis: Global Status, 2010, 52 pp. Gideon e-book series

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