TBEV

TBEV Full Name

Tick-borne encephalitis virus

TBEV Introduction

Tick-borne encephalitis virus (TBEV) is a neurotropic virus belonging to the genus Flavivirus within the family Flaviviridae. It is an enveloped, positive-sense single-stranded RNA (+ssRNA) virus. TBEV is primarily transmitted to humans through the bite of infected Ixodes ticks (I. ricinus in Europe and I. persulcatus in Asia/Russia), although alimentary transmission via unpasteurized milk from infected ruminants (goats, sheep, cows) can also occur. There are three main subtypes of the virus—European, Far Eastern, and Siberian—which vary in their virulence and geographical distribution.

Figure 1. Three-dimensional molecular (A) and schematic (B) structure of the tick-borne encephalitis virus (TBEV) virion. (Source: Mittova, V.et al. 2024)

Upon entry into the host, TBEV initially replicates in local immune cells, such as dendritic cells and neutrophils, near the site of the bite. This leads to a primary viremia (presence of virus in the blood), which corresponds to the initial clinical symptoms. The critical pathogenic mechanism of TBEV is its ability to breach the blood-brain barrier (BBB). Once inside the central nervous system (CNS), the virus directly infects neurons, causing direct neuronal damage and triggering a severe immunopathological response. This inflammation within the brain parenchyma and meninges is responsible for the severe neurological sequelae associated with the infection.

The primary clinical manifestation is Tick-borne Encephalitis (TBE). The disease typically follows a biphasic course:
1. Viremic Phase: The first phase presents with non-specific flu-like symptoms (fever, fatigue, headache, myalgia) lasting about 5 days.
2. Neurological Phase: After an asymptomatic interval of about one week, a second phase occurs in 20-30% of patients, characterized by CNS involvement. This can manifest as:
Meningitis: Inflammation of the membrane causing severe headache and fever.
Meningoencephalitis: Involving the brain tissue, leading to confusion, consciousness disturbances, and ataxia.
Meningoencephalomyelitis: The most severe form, involving the spinal cord and causing flaccid paralysis (often affecting the shoulder girdle and arms).

Alternate Names for TBEV

Tick-borne encephalitis virus; TBEV; Flaviviridae; Flavivirus

• 1. Mittova, V.et al. Tick-Borne Encephalitis Virus (TBEV): Epidemiology, Diagnosis, Therapeutic Approaches and Some Molecular Aspects—An Updated Review. Microbiol. Res. 2024, 15, 2619-2649.
  2. Martello E, et al. Systematic review on the non-vectorial transmission of Tick-borne encephalitis virus (TBEv). Ticks Tick Borne Dis. 2022 Nov;13(6):102028.