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Travel Health Information Sheets

Tick-Borne Encephalitis

Last updated: March 2012

 

Introduction

Tick-borne encephalitis (TBE) virus is a major human flavivirus and causes disease that impacts public health in endemic countries. Approximately 10,000 to 12,000 cases of TBE are reported annually world-wide; however this figure is felt to be much lower than the actual number of cases occurring [1].

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 (Figure)

Figure. 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 western and central Europe and is transmitted by Ixodes ricinus ticks. It is common in forest and mountainous regions of Austria, Estonia, Latvia, Lithuania, the Czech Republic, Slovakia, Germany, Hungary, Poland, Switzerland, western Russia, Ukraine, Belarus, Croatia and Slovenia.  It occurs at a lower frequency in Denmark, France, Kazakhstan, Liechtenstein, Italy, Romania, Norway, the Åland archipelago and neighbouring Finnish coastline, and Sweden. It is probable that TBE also occurs in Albania, Bosnia and Herzegovina, Bulgaria, Greece, Serbia and Montenegro and Moldova, although little data are available on the incidence of disease within these countries.

Thousands of cases of TBE occur each year from late spring to early autumn; between 2005 and 2009 the total number of annual cases in Western European countries averaged 3,000 [2]. 

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 Siberia and is also transmitted by I. persulcatus ticks. The virus has also been isolated in Kyrgyzstan and Mongolia [2].

TBE in United Kingdom travellers

Tick borne encephalitis is extremely rare in UK travellers. As of 22 February 2012, only a single confirmed case has been reported in a UK traveller who returned from the Czech Republic (central European TBE) in 2011.

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 un-pasteurised dairy products from infected animals.

The risk period for infection ranges from April to November, with infection with the Far Eastern subtype more common in the spring and the European subtype more common in the autumn.

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 [3].

Infected ticks are found on forest fringes with adjacent grassland, forest glades, riverside meadows and marshland, forest plantations with brushwood, and shrubbery.  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. Wet summers and mild winters tend to increase tick population density. In central Europe two peaks of activity have been observed: in May / June and again in September / October. In colder regions in northern Europe and in mountain regions these two peaks converge into a single peak in the summer [4].

The tick vectors are rarely found at altitudes of more than 1,000 metres, although some reports suggest ticks may be found up to 1,400m [5].

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. 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.

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 and central nervous system involvement with meningitis. About a third of these cases progress to encephalitis, which can result in paralysis.

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 is largely determined by the virus subtype. The Far Eastern subtype is generally more virulent, can lead to paresis, and is associated with a higher mortality (approximately 5 - 20% case fatality compared to 1 – 2% for the European subtype). There is currently little information on the virulence of the more recently described Siberian subtype.

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 insect bite avoidance methods. Travellers should be advised to:

  • Wear clothing with long sleeves and long trousers (tucked into socks), which can be treated with insecticide sprays such as permethrin.
  • Apply insect repellent to exposed skin.
  • Check the body for ticks regularly. After a tick has attached itself to the host it may not start feeding for approximately 12 hours [5]. The larval form of Ixodes ticks are tiny and difficult to see. 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. The 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 [7, 8]. Care needs to be taken not to squeeze the stomach contents into the site of the bite.

Travellers should also avoid consumption of un-pasteurised 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.

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.

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

Vaccine availability

TicoVac and TicoVac Junior vaccines (previously known 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 [9,10]

The Summary of Product Characteristics (SmPC) for the individual vaccines should be consulted prior to the administration of any vaccine (available at www.emc.medicines.org.uk)

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 3 – 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 3 – 5 year intervals if at risk

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

*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 [9].

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 [11]. 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

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. 

References

1. World Health Organization. Vaccines against tick-borne encephalitis: WHO position paper. Wkly Epidemiol Rec. 86: 241-256, 2011. [Accessed 13 March 2012]. Available at: http://www.who.int/wer/2011/wer8624.pdf

2. 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.

3. Health Protection Agency. Lindquist L, Vapalahti O. Tick-borne encephalitis. Lancet. 371:1861-71, 2008.

4. Mickiene A, Laiskonis A, Günther G et al. Tick-borne encephalitis in an area of high endemicity in Lithuania: disease severity and long-term prognosis. Clin Infect Dis. 35:650-8, 2002.

5. 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.

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

7. 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.

8. Pitches DW. Removal of ticks: a review of the literature. Eurosurveillance. 11, 2006. [Accessed 27 January 2012]. Available at: http://www.eurosurveillance.org/viewarticle.aspx?articleid=3027

9. Summary of Product Characteristics. TicoVac.  Updated 9 September 2009. [Accessed 27 January 2012]. Available at:  http://www.medicines.org.uk/EMC/medicine/20115/SPC/Ticovac

+0.5ml/

10. Summary of Product Characteristics. TicoVac Junior. Updated 27 January 2012. [Accessed 27 January 2012]. Available at: http://www.medicines.org.uk/EMC/medicine/20116/SPC/

Ticovac+0.25ml+Junior/

11. 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

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