Tick-borne encephalitis virus (TBEV)
Tick-borne encephalitis virus (TBEV) is the causative agent of tick-borne encephalitis (TBE), a potentially fatal neurological infection affecting humans and animals. TBEV is a member of the genus Flavivirus, within the family Flaviviridae. There are three main subtypes of the virus: European, Siberian and far-eastern. Vectors for TBEV are Ixodes ricinus and Ixodes persiculatus ticks.
Sample: CSF, 0,5 ml EDTA-blood
Modes of transmission
Tick-borne encephalitis virus is transmitted by tick bites and by consumption of unpasteurized goat’s milk.
The tick-borne encephalitis virus is known to first replicate at the site of inoculation and then in the lymph nodes that drain the inoculation site. Virus replication in the draining lymph nodes is followed by development of plasma viraemia. Haematogenic spread allows different organs to be infected, especially the reticulo-endothelial system (spleen, liver and bone marrow), and it is during this phase that the virus also crosses the blood–brain barrier to invade the central nervous system (CNS), where viral replication causes inflammation, lysis and cellular dysfunction. The incubation period is generally 7–14 days. Symptoms during the initial short febrile period can include fatigue, headache and pain in the neck, shoulders and lower back, accompanied by high fever and vomiting. This is often followed by an asymptomatic period lasting 2– 10 days and if the disease progresses to neurological involvement, this leads to the second phase, characterized by acute CNS symptoms with a high fever. CNS infection can manifest in the meninges (where inflammation causes meningitis), the brain parenchyma (to cause encephalitis), the spinal cord (myelitis), the nerve roots (radiculitis) or indeed any combination of these. In comparison with humans, domestic animals infected with TBEV are generally asymptomatic.
Active vaccination is the most effective method for preventing the tick-borne encephalitis virus, with modern vaccines shown to be safe and between 95 and 99% effective.
Prognosis depends on age of the patient, but recovery is generally difficult. Mortality rates for European, far-eastern and Siberian subtypes are 1-2%, 20-40% and 2-3%, respectively.
Increase in TBE morbidity had been observed, with an average of 8755 reported cases of TBE per year in Europe and Russia.
Wicki, R., Sauter, P., Mettler, C., Natsch, A., Enzler, T., Pusterla, N., Kuhnert, P., Egli, G., Bernasconi, M., Lienhard, R., et al. (2000). Swiss Army survey in Switzerland to determine the prevalence of Francisella tularensis, members of the Ehrlichia phagocytophila genogroup, Borrelia burgdorferi sensu lato, and tick-borne encephalitis virus in ticks. European Journal of Clinical Microbiology and Infectious Diseases 19, 427–432.