Health Professionals

Travel Health Information Sheets

Tick-Borne Encephalitis

Key messages:

Tick-borne encephalitis (TBE) virus can cause infection of the central nervous system which can lead to long-term neurological complications or death.


The disease is transmitted by the bite of infected ticks in parts of Europe and Asia and less commonly by the consumption of unpasteurised dairy products.


TBE is rarely reported in travellers but those visiting risk areas should reduce tick bites with protective clothing and insect repellents.


In risk areas, travellers should also regularly check their skin for attached ticks and remove them carefully.


An effective vaccine is available for those at risk.

Introduction

TBE virus is a major human flavivirus. It causes neuroinvasive disease and is a significant public health issue in endemic countries. Approximately 10,000 to 12,000 cases of TBE are reported annually; however this figure is considered to be much lower than the actual number of cases occurring [1]. In recent decades, the number of human cases in Europe has increased; endemic areas have spread northwards and to higher altitudes [2].

Travellers to endemic areas may be at risk when walking, camping or working in woodland terrain where they will be exposed to the tick vector. Infection may also be acquired by consuming unpasteurised dairy products from infected animals [2].

The TBE virus belongs to a closely related group of flaviviruses that includes yellow fever, dengue and Japanese encephalitis. TBE is caused by three different subtypes of TBE virus: European TBE virus, Far Eastern TBE virus and Siberian TBE virus.

Global epidemiology

TBE occurs in endemic areas across regions of 27 European countries and some Asian countries [2, 3]. Most cases are reported between Spring and Autumn [2] when there is increased exposure to the tick vector [1].

Figure 1: Tick-borne encephalitis risk areas *

Map from Health Information for Overseas Travel, 2010

 

View a larger version of the map (opens in a new window)

* Although the map represents information on endemic areas for TBE, it should be interpreted with caution as data may be incomplete, and the extent of epidemiological information available from different countries varies.

Information on the risk of TBE for specific countries can be found on the NaTHNaC Country Information Pages.

European TBE (or Central European encephalitis) is endemic in parts of central, eastern and northern Europe [2] and is transmitted by Ixodes ricinus ticks.

A map of risk areas in Europe can be found on the International Prevention Initiative on Tick-Borne Encephalitis website. The risk area extends to the west of Europe as far as Switzerland and the French region of Alsace [2]. The estimated number of clinical cases in European countries each year is 3,000 [3]. TBE has been included in the list of notifiable diseases in the European Union since September 2012 [3].

Far Eastern TBE (also known as Russian Spring/Summer encephalitis) is transmitted by I. persulcatus ticks, and occurs in the spring and summer months in eastern Russia and some countries in East Asia, particularly in forested regions of China and Japan.   

Siberian TBE (also known as west-Siberian encephalitis) is endemic in eastern Europe, Russia and northern Asia [2] and is also transmitted by I. persulcatus ticks. The virus has also been isolated in Kyrgyzstan and Mongolia [4].

Recent reports indicate that ticks may be found at altitudes up to 1,500m [1].

Risk for travellers

The risk of acquiring TBE infection is dependent on a number of factors including:

  •  Destination of travel

  •  Duration of travel in risk area
  •  Season of travel

  •  Activities undertaken

  •  Tick activity in the country visited

  •  Vaccination status of traveller

Travellers to endemic areas may be at risk when walking, camping or working in woodland terrain where they will be exposed to the tick vector. Infection may also be acquired by consuming unpasteurised dairy products from infected animals.

Transmission

Ixodes ticks are the main vectors of TBE virus. The virus is maintained in nature by small mammals (such as mice and voles), domestic livestock (including sheep, goats and cattle) and certain species of birds. Humans are incidental hosts for the TBE virus.

Transmission in humans occurs mainly through the bite of an infected tick with introduction of the virus via the tick saliva. As saliva contains an anaesthetic, the bite itself usually goes unnoticed. This emphasises the importance of checking the body for attached ticks. Unusually, humans may become infected after consumption of infected unpasteurised dairy produce [5].

Infected ticks are found on forest fringes with adjacent grassland, forest glades, riverside meadows and marshland, forest plantations with brushwood, and shrubbery. Ticks can also be found in parks and gardens [5].

They reside most commonly on ground level vegetation, on the underside of foliage, from where they can be brushed onto clothing or drop onto passing humans. Ticks are capable of transmitting the TBE virus throughout their lifecycle stages (larvae, nymphs or adults), and once infected, carry the virus for life.

Tick activity and development relate to climatic factors such as temperature, soil moisture and relative humidity.

The risk for infection of humans after a single tick bite varies between 1 in 200 and 1 in 1,000 in the different endemic areas [6].

Signs and symptoms

The typical course of TBE is biphasic. The incubation period is 7-14 days, with a range of 2-28 days [1]. The first clinical stage of the disease (which corresponds to the viraemic phase) may last from 1-8 days and affects two-thirds of infected patients. It is characterised by a non-specific flu-like illness with fatigue, headache, myalgia, nausea, general malaise and fever.

An interval of 1-20 days follows, during which time patients are usually asymptomatic [1]. Approximately a third of those who were symptomatic during the first phase proceed to a second phase of disease heralded by a sudden rise in temperature with central nervous system involvement such as meningitis, encephalitis, myelitis or radiculitis [1].

In up to 40 percent of encephalitic cases the disease results in permanent central nervous system sequelae, including neuropsychiatric and cognitive complaints [1].

The second phase of illness in children is usually limited to meningitis whereas adults older than 40 years are at increased risk of developing encephalitis, with higher mortality in those over the age of 60.

The clinical course of TBE disease may be determined by the virus subtype [1]. The Far Eastern subtype appears to be more severe. Case-fatality rates have been reported of ≥20 per cent for the Far Eastern subtype, six to eight per cent for the Siberian subtype, and one to two per cent for the European subtype [1].

Treatment

Treatment relies on supportive management; there is no specific anti-viral treatment for TBE

Prevention

The risk of acquiring TBE can be reduced by bite avoidance methods. Travellers should be advised to:

  • Avoid known heavily tick-infested areas of forest and woodland during the spring, summer and autumn where possible.
  • Wear clothing with long sleeves and long trousers (tucked into socks), which can be treated with insecticide sprays such as permethrin. Light coloured fabrics may be useful, as it is easier to see ticks against a light background.
  • Apply insect repellent to exposed skin. Repellents containing DEET, Icaridin or P menthane-3,8-diol (PMD) have been shown to be more protective than IR3535 containing repellents against Ixodes ricinus ticks [7].
  • Check the body for ticks regularly. The larval form of Ixodes ticks are tiny and difficult to see (they can be the size of a freckle or speck of dirt). Adult ticks, once they have fed and become engorged, may be the size of a coffee bean. Common areas for ticks to attach are at the hair-line, behind the ears, elbows, backs of knees, groin and armpits.
  • Remove ticks as soon as possible by using a pair of tweezers or tick remover. After a tick has attached itself to the host it may not start feeding for approximately 12 hours [8].
  • Removing the tick before it begins feeding may help reduce the risk of disease transmission. Tweezers should be placed as close as possible to the skin and then the tick pulled slowly, ensuring the mouth parts are removed completely. A steady, straight method is best for removal [5, 9, 10]. Care needs to be taken not to squeeze the stomach contents into the site of the bite. A skin disinfectant should be applied after the removal of the tick to reduce the risk of skin infection [5].

Travellers should also avoid consumption of unpasteurised dairy products in areas of risk.

TBE vaccination is available for those travellers intending to visit rural endemic areas, or whose occupation may put them at higher risk (see below).

Tick-Borne Encephalitis Vaccine

Indications for use of TBE vaccine

Tick borne encephalitis vaccine should be considered for:

  • All persons living in TBE-endemic areas.
  • Those at occupational risk in endemic areas, e.g. farmers, forestry workers, soldiers
  • Travellers to rural endemic areas during late spring, summer and autumn e.g. campers, hikers, Scout /Guide groups.
  • Laboratory workers who may be exposed to TBE

Vaccine availability

TicoVac and TicoVac Junior vaccines (known in some countries as FSME IMMUN and FSME IMMUN Junior) are licensed in the UK.

Details of these vaccines can be found in the summary table below.

Vaccine schedules [11, 12]

The Summary of Product Characteristics (SmPC) for the individual vaccines should be consulted prior to the administration of any vaccine.

 

Vaccine

Manufacturer

Schedule

Accelerated schedule

Length of protection

Age range

TicoVac 0.5ml

 

Baxter

 

Currently distributed by MASTA

3 doses on days 0, between 1 and 3 months, and 5 to 12 months after the second dose*

2nd dose can be given 2 weeks after the 1st dose

**First booster no more than 3 years after 3rd dose. After this, boosters may be given at 5 year intervals if at risk

Persons at least 16 years of age and older

TicoVac 0.25ml Junior

 

Baxter

 

Currently distributed by MASTA

3 doses on days 0, between 1 and 3 months and 5 to 12 months after the second dose*

2nd dose can be given 2 weeks after the 1st dose

First booster no more than 3 years after 3rd dose. After this, boosters may be given at 5 year intervals if at risk

Children above 1 year of age and below 16 years of age

* After the first two doses, sufficient protection can be expected for the ongoing tick season (protection rate over 90% after the second dose)

**In those aged > 60 years, booster intervals should not exceed three years (see below).

The optimum time to begin the course of vaccination against TBE is during the winter months in order to ensure protection prior to the start of the tick season in spring.

TicoVac is effective against the Far Eastern and Siberian subtypes as well as the European subtype of TBE [11].

Serologic studies indicate that the persistence of TBE immunity is compromised in the elderly and they have a more rapid decline of antibodies. The immune response following booster doses of vaccine is also of lower magnitude in the elderly compared to that in younger adults [13]. Because of these findings, booster doses continue to be recommended every three years in adults > 60 years.

Contraindications

  • Current febrile illness
  • Allergies to constituents of the vaccine, including severe  reactions to egg

Precautions

  • Persons with known or suspected auto-immune disease
  • Persons with pre-existing cerebral disorders
  • Pregnancy
  • Lactation

In children with a history of fever convulsions or high fever following vaccinations, antipyretic prophylaxis or treatment may be considered.

Adverse events

Adverse reactions following TBE vaccine are most commonly mild and transient. In adults they include local reactions such as swelling, redness and pain at the injection site. Generalised reactions such as fatigue, malaise, headache, muscle pain and nausea have been reported but were transient and usually mild.

Studies in children reported mild local and systemic reactions. The most common local reactions reported were pain and tenderness at the injection site. The most frequently reported systemic reactions were fever and restlessness in young children, as well as headache in all children. Fever, particularly after the first dose, has been reported.

In rare cases, more serious reactions of meningitis and neuritis have occurred. 

Advice if bitten by a tick in a TBE risk country

TBE immunoglobulin (TBE IG) was previously used as post-exposure prophylaxis after a tick bite in TBE endemic countries. However, there were concerns that it had a negative effect on the course of disease. TBE IG is no longer recommended in the UK or other European countries for post-exposure prophylaxis.

If a traveller is bitten by a tick in an area of risk for TBE, they should remove the tick with tweezers as soon as possible (see above). If any signs of illness occur within 28 days of a tick bite, advice should be promptly sought from a medical practitioner.

References

1. World Health Organization. Vaccines against tick-borne encephalitis: WHO position paper. Wkly Epidemiol Rec. 86: 241-256, 2011. [Accessed 4 September 2014]. Available at: http://www.who.int/wer/2011/wer8624.pdf

2. European Centre for Disease Prevention and Control, Technical Report: Epidemiological situation of tick-borne encephalitis in the European Union and European Free Trade Association countries. September 2012, [Accessed 4 September 2014]. Available at: http://www.ecdc.europa.eu/en/publications/_layouts/forms/Publi

cation_DispForm.aspx?List=4f55ad51-4aed-4d32-b960-af70113dbb90&ID=683

3. Haditsch., Kunze, U. Tick-borne encephalitis: A disease neglected by travel medicine. Travel Medicine and Infectious Disease (2013) Sep-Oct; 11(5):295-300

4. Süss J. Tick-borne encephalitis 2010: Epidemiology, risk areas, and virus strains in Europe and Asia – An overview. Ticks and Tick-borne Diseases. 2:2-15, 2011.

5. World Health Organization Regional Office for Europe and European Centre for Disease Prevention and Control, Tick-Borne Encephalitis in Europe. April 2014, [Accessed 4 September 2014] Available at: http://www.euro.who.int/en/about-us/whd/world-health-day-2014/fact-sheets-world-health-day-2014-vector-borne-diseases/fact-sheet-tick-borne-encephalitis-in-europe

6. Suss J. Epidemiology and ecology of TBE relevant to the production of effective vaccines. Vaccine.  21 (Suppl 1):19–35, 2003.

7. Lupi, E., Hatz, C., Schlagenhauf, P. The efficacy of repellents against Aedes, Anopheles, Culex and Ixodes spp. - A literature review. Travel Medicine and Infectious Disease, 2013; Nov-Dec;11(6):374-411  

8. Daniel M, Dantclova V, Kriz B et al. Shift of the tick Ixodes ricinus and tick-borne encephalitis to higher altitudes in Central Europe. Eur J Clin Microbiol Infect Dis.  22:327 – 8, 2003.

9. Teece S, Crawford I. Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary. How to remove a tick. Emerg Med J. 19:323–4, 2002.

10. Pitches DW. Removal of ticks: a review of the literature. Eurosurveillance. 11, 2006. [Accessed 4 September 2014]. Available at: http://www.eurosurveillance.org/viewarticle.aspx?articleid=3027

11. Summary of Product Characteristics. TicoVac.  Updated March 2014, [Accessed 4 September 2014]. Available at: http://www.ecomm.baxter.com/ecatalog/browseCatalog.do?lid=

10011&hid=10000&cid=10001&key=4c9308615c2d041e33eba

c65d14b5b&pid=508131

12. Summary of Product Characteristics. TicoVac Junior. Updated 2 March 2014, [Accessed 4 September 2014]. Available at: http://www.ecomm.baxter.com/ecatalog/browseCatalog.do?lid=

10011&hid=10000&cid=10001&search_value=ticovac

13. Rendi-Wagner P, Zent O, Jilg W et al. Persistence of antibodies after vaccination against tick-borne encephalitis. Int J Med Micro. 296 (Suppl 1):202–7, 2006.

Reading list

Field VK, Ford L, Hill DR, eds. Health information for overseas travel. National Travel Health Network and Centre, London, 2010

Links

Public Health England: Tick-borne encephalitis

Public Health England: Ticks and your health, Information about tick bite risks and prevention

Public Health England: Immunisation against infectious disease ‘Green book’ Chapter 31

European Centre for Disease Control and Prevention: Tick-borne diseases

International Scientific Working Group on TBE

U.S Centres for Disease Control and Prevention: Tick borne diseases abroad

NHS Choices: Tick-borne encephalitis

Advice current at: 4 September 2014