Tick-borne encephalitis

Tick-borne meningoencephalitis
Infected countries/areas in Eurasia
Classification and external resources
Specialty infectious disease
ICD-10 A84
ICD-9-CM 063
DiseasesDB 29274
Patient UK Tick-borne encephalitis
MeSH D004675

Tick-borne encephalitis (TBE) is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis, or meningoencephalitis. Although TBE is most commonly recognized as a neurological disorder, mild fever can also occur. Long-lasting or permanent neuropsychiatric consequences are observed in 10 to 20% of infected patients.

The number of reported cases has been increasing in most countries.[1]

The tick-borne encephalitis virus is known to infect a range of hosts including ruminants, birds, rodents, carnivores, horses, and humans. The disease can also be spread from animals to humans, with ruminants and dogs providing the principal source of infection for humans.[2]

TBE, like Lyme disease, is one of the many tick-borne diseases.

Signs and symptoms

Symptoms of TBE-infection

The virus can infect the brain (encephalitis), the meninges (meningitis) or both (meningoencephalitis).[3] In general, mortality is 1% to 2%, with deaths occurring 5 to 7 days after the onset of neurologic signs.

In dogs, the disease also manifests as a neurological disorder with signs varying from tremors to seizures and death.[2]

In ruminants, neurological disease is also present, and animals may refuse to eat, appear lethargic, and also develop respiratory signs.[2]

Cause

TBE is caused by tick-borne encephalitis virus, a member of the genus Flavivirus in the family Flaviviridae. It was first isolated in 1937. Three virus sub-types are described: European or Western tick-borne encephalitis virus, Siberian tick-borne encephalitis virus, and Far-Eastern tick-borne encephalitis virus (formerly known as Russian spring summer encephalitis virus).

Russia and Europe report about 5,000–7,000 human cases annually.[1][4]

The former Soviet Union conducted research on tick borne diseases, including the TBE viruses.

Transmission

Sheep ticks (Ixodes ricinus) ,such as this engorged female, transmit the disease

It is transmitted by the bite of several species of infected ticks, including Ixodes scapularis, I. ricinus and I. persulcatus,[5] or (rarely) through the non-pasteurized milk of infected cows.[6]

Diagnosis

The TBE virus may be present in a seronegative strain or subtype. In such cases a marker for TBE infection is elevated IFN-g in CSF.

Viral antigen can usually be found in brain tissue. Serological testing can also be performed with an ELISA.[2]

Treatment and prevention

A sign in Lithuanian forest, warning about a high probability to be infected by tick-borne encephalitis

The disease is incurable once manifested, so there is no specific drug therapy for TBE. Symptomatic brain damage requires hospitalization and supportive care based on syndrome severity. Anti-inflammatory drugs, such as corticosteroids, may be considered under specific circumstances for symptomatic relief. Tracheal intubation and respiratory support may be necessary.

Prevention includes non-specific (tick-bite prevention, tick checks) and specific prophylaxis in the form of a vaccine. TBE immunoglobulin is no longer used. Tick-borne encephalitis vaccine is very effective and available in many disease endemic areas and in travel clinics.[7]

Epidemiology

The disease is most common in Central and Eastern Europe, and Northern Asia. About ten to twelve thousand cases are documented a year but the rates vary widely from one region to another.[8] Most of the variation is the result of variation in host population, particularly that of deer. In Austria, an extensive free vaccination program since the 1960s has reduced incidence by roughly 85%.[9] In Sweden, most cases of TBE occur in a band running from Stockholm to the west, especially around lakes and the nearby region of the Baltic sea.[10][11] This reflects the greater population involved in outdoor activities in these areas. Although in some regions of Russia and Slovenia the prevalence of cases can be as high as 70 cases per 100,000 people per year, in most regions it is far lower, and overall, for Europe the estimated risk is roughly 1 case per 10,000 human-months of woodland activity.[9][12] Travelers to endemic regions do not experience many cases, with only 5 cases reported among U.S. travelers returning from Eurasia between 2000-2011, a rate so low that the U.S. Centers for Disease Control and Prevention recommend vaccination only for those who will be extensively exposed in high risk areas.[13]

References

  1. 1 2 Suss J (June 2008). "Tick-borne encephalitis in Europe and beyond--the epidemiological situation as of 2007". Euro Surveill. 13 (26). PMID 18761916.
  2. 1 2 3 4 Tickborne Encephalitis Virus reviewed and published by WikiVet, accessed 12 October 2011.
  3. ↑ Kaiser R (September 2008). "Tick-borne encephalitis". Infect. Dis. Clin. North Am. 22 (3): 561–75, x. PMID 18755391. doi:10.1016/j.idc.2008.03.013.
  4. ↑ Salisbury, Dr David; Noakes, Dr Karen (2006). Immunisation against infectious disease (Third ed.). TSO (The Stationery Office - UK Department Of Health). pp. 385–390. ISBN 978-0-11-322528-6
  5. ↑ Dumpis U, Crook D, Oksi J (April 1999). "Tick-borne encephalitis". Clin. Infect. Dis. 28 (4): 882–90. PMID 10825054. doi:10.1086/515195.
  6. ↑ CDC Yellow Book, accessed 5 October 2013.
  7. ↑ Demicheli V, Debalini MG, Rivetti A (2009). Demicheli V, ed. "Vaccines for preventing tick-borne encephalitis". Cochrane Database Syst Rev (1): CD000977. PMID 19160184. doi:10.1002/14651858.CD000977.pub2.
  8. ↑ "Vaccines against tick-borne encephalitis: WHO position paper." (PDF). Releve epidemiologique hebdomadaire / Section d'hygiene du Secretariat de la Societe des Nations = Weekly epidemiological record / Health Section of the Secretariat of the League of Nations. 86 (24): 241–56. 10 June 2011. PMID 21661276.
  9. 1 2 Amicizia, Daniela; Domnich, Alexander; Panatto, Donatella; Lai, Piero Luigi; Cristina, Maria Luisa; Avio, Ulderico; Gasparini, Roberto (2013-05-14). "Epidemiology of tick-borne encephalitis (TBE) in Europe and its prevention by available vaccines". Human Vaccines & Immunotherapeutics. 9 (5): 1163–1171. ISSN 2164-5515. PMC 3899155 Freely accessible. PMID 23377671. doi:10.4161/hv.23802.
  10. ↑ Pettersson, John H.-O.; Golovljova, Irina; Vene, Sirkka; Jaenson, Thomas G. T. (2014-01-01). "Prevalence of tick-borne encephalitis virus in Ixodes ricinus ticks in northern Europe with particular reference to Southern Sweden". Parasites & Vectors. 7: 102. ISSN 1756-3305. PMC 4007564 Freely accessible. PMID 24618209. doi:10.1186/1756-3305-7-102.
  11. ↑ team, European Centre for Disease Prevention and Control (ECDC)-Health Communication Unit- Eurosurveillance editorial. "Tick-borne encephalitis increasing in Sweden, 2011". Retrieved 2016-06-04.
  12. ↑ team, European Centre for Disease Prevention and Control (ECDC)-Health Communication Unit- Eurosurveillance editorial (2011-03-11). "Case report: Tick-borne encephalitis in two Dutch travellers returning from Austria, Netherlands, July and August 2011". Retrieved 2016-06-04.
  13. ↑ "Tickborne Encephalitis - Chapter 3 - 2016 Yellow Book | Travelers' Health | CDC". wwwnc.cdc.gov. Retrieved 2016-06-04.
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