Tick-borne Encephalitis (TBE) is caused by a flavivirus - the same family as yellow fever and japanese encephalitis.

Pathogenesis

It is usually spread by bites from ticks that are infected with the disease. Unpasteurised milk, especially from goats, is also implicated in spreading the disease.

The incubation time is 7-14 days. People initially develop a flu-like illness that lasts approximately 7 days. This may progress to encephalitis with headache, fever, confusion, agitation and vomiting. Coma may follow. It is fatal in 1 in 30 cases.¹

The virus sub-type has a bearing on the course of the disease. The Eastern variant is more virulent, and leads to severe disease more often than the central one.

Epidemiology

It is endemic to Russia, Eastern and Central Europe. The area spreads from the Rhine to the Urals, from Scandinavia to Italy and Greece. It is also endemic in Japan. Transmission mainly occurs in spring and summer, particularly in rural areas.

There has been an observed increase in the number of cases of TBE in recent years. This is thought to reflect a generally warmer climate, with an increase in numbers of ticks and rodents. In Europe 11,356 cases were reported in 1999. 83% of those occurred in Russia.¹ Symptomatic disease has been observed in all age groups.

Available vaccine

There is no specific treatment for TBE once infected.
Prevention consists of:

• Individual prophylactic measures, e.g. self-examination, extracting ticks after exposure and use of insect repellant.
• Immunisation if travelling/spending time in endemic or high risk areas.

There is only one licensed vaccine available in the UK: FSME-Immun® available from MASTA. Tel. 0113 2387555.

Austria has reported a sharp decline in cases in vaccinated areas and a vaccine efficacy rate of 99%.² The main adverse effect reported is fever.

Vaccine schedule

Ideally immunisation should be completed at least a month before travel. It is considered to be effective against all strains of the disease.

Contraindications

• Anaphylaxis:
  • Should not be given to those who have had a confirmed anaphylactic reaction within 72 hours of a previous dose of the same vaccine.⁴
  • Also confirmed reaction to a constituent of the vaccine:
    • TBE vaccine is produced in egg protein.
    • Allergy testing should be performed with diluted vaccine.
• Other severe adverse reactions:
  • This means an extensive area of redness and swelling affecting a large area of the arm or leg, accompanied by a fever of 39.5 degrees or higher, within 48 hours of the injection.
• The following DO NOT contraindicate vaccination:
  • A personal or family history of asthma, allergy, hay fever or eczema
  • Prematurity
  • Stable neurological conditions, e.g. cerebral palsy, Down's syndrome or epilepsy
  • Contact with infectious disease
  • Treatment with antibiotics or local corticosteroids
  • Child is being breastfed or mother is pregnant
  • Being underweight
  • Taking replacement corticosteroids

Special circumstances

• Acute illness - postpone immunisation until recovered. Minor infections, without fever or systemic upset are not reasons to postpone.⁴
• Pregnancy - inactive vaccine is probably safe. The risks to the fetus are likely to be negligible. It should only be administered during pregnancy and to breastfeeding women when it is considered urgent to achieve protection against TBE infection and after careful consideration of the risk-benefit relationship.⁵ There is some evidence that it provides protection to unvaccinated newborns, who may have a particularly severe disease course.⁶
• Immunosuppression or HIV - inactivated vaccines can be given, regardless of CD4 count. However these individuals may not be able to mount a full immune response.

Document references

1. World Health Organisation; State of the art of new vaccines-research and development.
2. Heinz FX, Holzmann H, Essl A, et al; Field effectiveness of vaccination against tick-borne encephalitis. Vaccine. 2007 Oct 23;25(43):7559-67. Epub 2007 Aug 31. [abstract]
3. Immunisation against infectious disease - 'The Green Book', Dept of Health (various dates)
4. Immunizations - travel vaccinations, Clinical Knowledge Summaries (2007)
5. Summary of Product Characteristics. Ticovac ® 0.5ml. MASTA ltd. Electronic Medicines Compendium. Text updated October 2007. Accessed May 2009.
6. Jones N, Sperl W, Koch J, et al; Tick-borne encephalitis in a 17-day-old newborn resulting in severe neurologic impairment. Pediatr Infect Dis J. 2007 Feb;26(2):185-6. [abstract]

Internet and further reading

• National Travel Health Network and Centre
• CDC; Tick-borne Encephalitis. August 2005.
• Health information for overseas travel 'Yellow Book'; Health Information for Overseas Travel 'Yellow Book', National Health Travel Network and Centre (NaTHNAC)

Acknowledgements