Transmission of TBE to humans usually takes place during a tick bite through the saliva of an infected tick, although unpasteurised dairy products from infected animals can also pose a risk.¹

Ticks are the main vectors and reservoir hosts of the TBE virus. Ticks can get infected with TBE through co-feeding, feeding on a viremic host or occasionally transovarially from infected females to eggs.¹

Not all ticks spread TBE. But in highly endemic^† areas up to 40% of ticks carry the virus, although prevalence varies considerably by region³, see ‘Who is at risk?’ section below.

^† Endemic areas are where an infection in a population is constantly maintained at a controllable level.

Location
TBE has been reported in over 35 countries. TBE infected ticks can be found across parts of Europe, including some parts of the UK, North Africa and Asia.^3,4

Reports of TBE are generally at altitudes lower than 1500 metres. However, ticks have been noted at higher altitudes, thought to be as a result of climate change.⁵

Time of year
Ticks are typically active when temperatures are above 6º Celsius, usually from March to November. However, the tick season can vary each year depending on the climate.¹

Activity
Ticks live outside and near the ground but can be found both within or outside cities, in parks, gardens and forests.⁵

Outdoor activities can put you at risk of coming into contact with ticks; for example, if you take part in activities in grassy areas where ticks are commonly found.⁵

For most people infected with the TBE virus, there are no symptoms but if there are, they usually appear up to 2 weeks after being bitten and follow 2 phases:⁶

1st Phase: Flu-like symptoms for 2-7 days followed by an asymptomatic period for 2-10 days. Fever, headache, tiredness, nausea, muscle pain.

2nd Phase: Involving the neurological system with symptoms of meningitis and/or encephalitis. High fever, headache, fatigue, nausea, vomiting and vertigo.

Most people infected recover fully, but 35 to 58% of people with TBE develop post-encephalitic syndrome (PES), which causes serious long-term complications including paralysis.⁶

The European TBE subtype has a mortality rate of 0.5-2% - this means that up to 1 in every 50 people who develop symptoms upon contracting this subtype of TBE will die from this infection. The Siberian subtype is associated with a mortality rate of 1-3% and the Far Eastern subtype has mortality rates of up to 35%.