Tick-borne encephalitis (TBE)

Tick-borne encephalitis (TBE) is caused by members of the flavivirus family that can affect the central nervous system

• although TBE is most commonly recognised as a meningo-encephalitis, mild febrile illnesses can also occur
• there are three versions of the disease related to the virus subtypes, namely European, Far Eastern and Siberian
• TBE is transmitted to humans by the bite of an infected tick or, less commonly, by ingestion of unpasteurised milk from infected animals, especially goats
• virus is maintained in nature by small mammals, domestic livestock and certain species of birds
• more men tend to be infected than women and most of these infections are caused by leisure activity such as hiking and walking
• incidence peaks in spring and early summer, but can occur throughout the year
• incubation period is from two to 28 days
• European version
  • biphasic with an initial viraemic phase of fever and influenza-like symptoms followed in some cases (after an afebrile period of one to 20 days) by central nervous system involvement
  • case fatality rate of the European version is 1%
  • long-lasting or permanent neuropsychiatric sequelae are observed in 10–20% of affected patients
• Far Eastern version
  • more gradual in onset and normally takes a more severe and longer course
  • reported mortality of 5–20%.
• TBE occurs in most or parts of Austria, Germany, southern and central Sweden, Hungary, France (Alsace region), Switzerland, Norway, Denmark, Poland, Croatia, Albania, the Baltic states (Estonia, Latvia and Lithuania), the Czech and Slovak Republics, Hungary, Russia (including Siberia), Ukraine, some other countries of the former Soviet Union, and northern and eastern regions of China
• the second case of TBE was reported in the UK on 31/7/2020 (2)

Prevention is by wearing appropriate clothing, removing ticks before they start feeding, immunisation (Austria has vaccinated its entire population).

• awareness of risk areas is essential
• following measures are advised whether or not vaccine is given
  • some protection against TBE is provided by covering arms, legs and ankles, and using insect repellents on socks and outer clothes
  • any ticks attaching to the skin should be removed as soon as possible, ensuring complete removal of the ticks. Evidence suggests that the best method is slow, straight removal with tweezers
  • unvaccinated individuals bitten by ticks in endemic areas should seek local medical advice
  • unpasteurised milk should not be drunk. The vaccine is recommended particularly for spring and summer travel in warm, forested parts of the endemic areas, when ticks are most prevalent. Tourists who hike, camp, hunt and undertake fieldwork in endemic forested areas should be vaccinated
  • TBE vaccine is recommended for those who will be going to reside in an area where TBE is endemic or epidemic and particularly those working in forestry, woodcutting, farming and the military
  • laboratory workers who may be exposed to TBE should be vaccinated

A risk assessment, published by a multi-agency cross-government committee, reports that tick borne encephalitis is now likely to be present in England (3)

Reference:

1. Immunisation Against Infectious Disease - "The Green Book".Chapter 31 Tick-borne encephalitis (April 2019)
2. Public Health England (July 31st 2020). Rare tick-borne infections diagnosed in England.
3. UK Health Security Agency (April 2023). Tick-borne encephalitis detection in England.