Background
- Single-stranded, positive-sense RNA virus in the Flaviviridae family, genus Flavivirus
- Three subtypes, Far Eastern (TBEV-FE), Siberian (TBEV-Sib), and European (TBEV-Eu)
- Greatest number of cases reported in Czech Republic, Lithuania, Latvia, Germany, and Slovenia
- Transmitted by Ixodes ticks
- Also has transovarial and transstadial transmission, and may be transmitted between ticks feeding on the same host
- Mostly in sheltered microhabitats with high humidity, moderate temperatures, up to 2100 m elevation
- Reservoirs include numerous birds and mammal hosts; humans are incidental in the transmission cycle
| Subtype | Distribution | Vector |
|---|---|---|
| Far Eastern (TBEV-FE) | eastern Russia, Korea, China, parts of Japan, and parts of the Baltic | Ixodes persulcatus, Ixodes ovatus (Japan), Haemaphysalis (Korea) |
| Siberian (TBEV-Sib) | Russia | Ixodes persulcatus |
| European (TBEV-Eu) | Scandinavia, Europe, and eastern states of the former Soviet Union | Ixodes ricinus |
Clinical Manifestations
- Incubation period of 8 days (range 4 to 28 days)
- Illness begins with non-specific influenza-like illness, with fever, malaise, headache, nausea, vomiting, and myalgias
- Initial symptoms resolve within a week, and for most people, nothing further happens
- In severe disease, however, symptoms return within 2 to 8 days (range 1 to 20 days), with high fever, headache, and vomiting
- Spectrum of disease from aseptic meningitis to meningoencephalitis to poliomyelitis-like flaccid paralysis or polyradiculoneuritis Guillain-Barré-like paralysis
- Symptoms are most severe in the elderly and mostly mild in children
- Most severe form is with TBEV-FE, where mortality is about 20% among hospitalized patients and 60% of survivors having neurologic sequelae
- Mortality is 6 to 8% for TBEV-Sib and 1-2% for TBEV-Eu
