Citation, DOI and article data
Tick-borne encephalitis (TBE), a zoonotic disease, occurring as a result of tick-borne encephalitis virus (TBEV) infection, is a recognized flavivirus encephalitis and an increasingly considered differential diagnosis globally 1.
Tick-borne encephalitis is endemic to Asian, eastern European, Baltic and Nordic countries 2. The number of confirmed tick-borne encephalitis cases in Europe specifically has increased by almost 400% in recent decades, with a reported annual incidence of 10,000-12,000 3,4. Infection rate peaks over the summer months, with higher risk associated with outdoor activity, particularly in woodland areas.
Initial symptoms following infection with European tick-borne encephalitis virus subtypes are often biphasic in nature and will typically occur within 14 days. These include marked pyrexia, myalgia, fatigue and vomiting. Following a short asymptomatic period, the pyrexia returns with signs of central nervous system involvement. This may manifest as one or more of:
Cranial nerve involvement has been reported 5.
Less commonly, there is no asymptomatic period i.e. the infection is monophasic in presentation: this is frequently seen with the more aggressive Far Eastern subtype.
Tick-borne encephalitis virus is in the mammalian tick-borne flavivirus group of Flaviviridae, which are single-stranded RNA viruses. There are three subtypes of tick-borne encephalitis viruses, the most virulent being the Far Eastern subtype 2.
Imaging is consistent with inflammation of the involved central nervous system anatomy, which is of broad etiology. However, tick-borne encephalitis has a few anatomical predilections on MRI that may aid in developing a differential diagnosis, along with positive IgM and IgG serology 5:
- T1: involvement of the meninges may be more pronounced in the cerebellar folia and the basal cisterns
- T2/FLAIR/DWI: focal or diffuse hyperintensities within the thalami, basal ganglia, cerebellum and anterior horns of the spinal cord
Of note, contrast medium enhancement is rare.
Treatment and prognosis
There is currently no treatment for tick-borne encephalitis and vaccination is encouraged. Although the risk of death is small, long term neurological sequelae - mainly gait disturbance - occur in approximately half of patients and may persist for several years 6.
- 1. Epidemiological situation of tick-borne encephalitis in the European Union and European Free Trade Association countries. European Centre for Disease Prevention and Control. 2012.
- 2. Pulkkinen LIA, Butcher SJ, Anastasina M. Tick-Borne Encephalitis Virus: A Structural View. (2018) Viruses. doi:10.3390/v10070350 - Pubmed
- 3. Mansfield KL, Johnson N, Phipps LP, Stephenson JR, Fooks AR, Solomon T. Tick-borne encephalitis virus - a review of an emerging zoonosis. (2009) The Journal of general virology. 90 (Pt 8): 1781-94. doi:10.1099/vir.0.011437-0 - Pubmed
- 4. Süss J, Klaus C, Diller R, Schrader C, Wohanka N, Abel U. TBE incidence versus virus prevalence and increased prevalence of the TBE virus in Ixodes ricinus removed from humans. (2006) International journal of medical microbiology : IJMM. 296 Suppl 40: 63-8. doi:10.1016/j.ijmm.2005.12.005 - Pubmed
- 5. Marius Horger, Robert Beck, Michael Fenchel, Ulrike Ernemann, Thomas Nägele, Harald Brodoefel, Stefan Heckl. Imaging Findings in Tick-Borne Encephalitis With Differential Diagnostic Considerations. (2012) American Journal of Roentgenology. 199 (2): 420-7. doi:10.2214/AJR.11.7911 - Pubmed
- 6. Kaiser R. Tick-borne encephalitis: Clinical findings and prognosis in adults. (2012) Wiener medizinische Wochenschrift (1946). 162 (11-12): 239-43. doi:10.1007/s10354-012-0105-0 - Pubmed