Tick-borne encephalitis virus (TBEV) infects small rodents, with humans being inadvertent hosts. It is a member of the Flaviviridae family, genus Flavivirus and there are three subtypes; Siberian tick-borne encephalitis virus, European/Western tick-borne encephalitis virus and Far eastern Tick-borne encephalitis virus (formerly known as Russian Spring Summer encephalitis virus, RSSEV). TBEV is an enveloped virus containing a capsid and single stranded RNA genome.
TBEV causes tick-borne encephalitis. There are two stages to the disease, the clinical signs for each are described below:
First stage clinical signs (lasting 1-8 days)
- Muscle pain
Second stage clinical signs
30% of cases progress into the second stage where meningitis (inflammation of the membranes surrounding the brain and spinal cord) or encephalitis (inflammation of the brain) can develop, causing damage to the central nervous system. Recovery can be over a few weeks, but it may take several months or years to fully recover. 1 in 10 people develop long-term problems.
- Sudden fever
- Nausea and vomiting
- Stiff neck
- Changes in mental state, such as confusion, drowsiness or disorientation
- Sensitivity to bright light (photophobia)
- Inability to speak
- Changes in personality and behaviour
- Death (1-2% in European TBE, 5-20% in Far-eastern TBE)
TBEV is transmitted by hard ticks of the family Ixodidae, which act as both the vector and reservoir for TBEV. The virus is able to transfer from adult ticks to larvae during their life cycle, and the adults infect small rodents by taking blood meals from them. Consumption of raw milk from infected goats, sheep and cows can also occur, as well as being passed from the mother during pregnancy.
Tick-borne encephalitis (TBE) is present across Eurasia. The disease tends to occur focally even within endemic areas. Humans are most likely to be infected between April and November in rural areas.
Impact for Society – what are we doing?
Very little is known about antiviral responses in ticks at the cellular and molecular level. At the Institute, work is underway to discover whether tick immune responses to viruses are the same as insect responses and to find new genes and proteins that are involved in the interaction between tick cells and the virus. By extending knowledge of the tick hosts, the Institute will be better informed as to how TBEV is spread, which will aid in informing prevention strategies in the future.