Tick-borne encephalitis virus

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Transmission electron micrograph of TBE virus[1]

Tick-borne encephalitis (TBE) virus is a tick-borne flavivirus transmitted by various Ixodes spp across Europe and Asia.

This disease, though extremely rare in dogs, is often acutely fatal with few prodromal signs. In humans, an estimated number of 10,000 cases in Russia and 3,000 cases in Europe occur annually[2], characterized by fever, encephalitis and a fatality rate up to 35%[3].

The disease is transmitted by ''Ixodes ricinus, Ixodes persulcatus and Ixodes ovatus[4].

Dogs become readily infected with TBE virus but they are accidental hosts not capable to further spread the virus.

They seroconvert upon infection but they seem to be much more resistant to the clinical disease than humans[5]. Owing to the increased mobility of people traveling to endemic areas with their companion dogs, this consequently leads to problems in recognizing and diagnosing this severe infection in a yet non-endemic area.

The incubation period in dogs varies from one to two weeks, with infected dogs presenting with acute fever, vestibular syndrome, optic neuritis[6], ataxia, tetraparesis and behaviour changes (e.g. aggression), reflecting multifocal neurological disorders in the cerebrum and the brain stem.

Most dogs progress to development of motor failures either on the fore- or hindlimbs with reduced proprioception and hyporeflexy in front and/or rear legs. Seizures and acute encephalitis inevitably ensue[7][8][9][10].

Although dogs present with hematological changes reflecting panleucopenia, and postmortem findings alluding to a nonsuppurative meningoencephalitis without visceral organ involvement[11], diagnosis relies specifically on PCR assay identification of the virus[8].

Death appears inevitable in most cases regardless of medical intervention.

The few dogs which survive, due primarily to aggressive supportive therapy and judicious use of nonsteroidal anti-inflammatories, require a period of 6 - 12 months to fully recover[12].

Tick control is essential to prevent exposure to viral-laden ticks and vaccination of dogs with the human TBE-vaccine is considered an effective preventive measure in highly endemic areas[5].

References

  1. Punkkiklinikka
  2. Charrel RNet al (2004) Tick-borne virus diseases of human interest in Europe. Clin Microbiol Infect 10(12):1040–1055
  3. Pugliese A et al (2007) Emerging and re-emerging viral infections in Europe. Cell Biochem Funct 25(1):1–13
  4. Takashima I et al (1997) A case of tick-borne encephalitis in Japan and isolation of the virus. J Clin Microbiol 35(8):1943–1947
  5. 5.0 5.1 Pfeffer M & Dobler G (2011) Tick-borne encephalitis virus in dogs - is this an issue? Parasit Vectors 4:59
  6. Stadtbäumer K et al (2004) Tick-borne encephalitis as a possible cause of optic neuritis in a dog. Vet Ophthalmol 7(4):271-277
  7. Tipold A et al (1993) Zentraleuropäische Zeckenenzephalitis beim Hund. Kleintierpraxis 38:619–628
  8. 8.0 8.1 Weissenböck H et al (1998) Tick-borne encephalitis in dogs: neuropathological findings and distribution of antigen. Acta Neuropathol 95:361–366
  9. Reiner B & Fischer A. Frühsommer-Meningoenzephalitis (FSME) beim Hund in Deutschland: Zwei Fallberichte. Kleintierpraxis 43:255–269
  10. Greisikova M et al (1972) Isolation of tick-borne encephalitis virus from the brain of a sick dog in Switzerland. Acta Virol (Praha) 16:88
  11. Weissenböck H & Holzman H. Immunhistologischer Nachweis der Frühsommer-Meningoencephalitis beim Hund in Österreich. Wien Tierärztl Mschr 84:34–38
  12. Kritz G et al (2001) Ixodes ricinus: Gemeingefährlich für Hundes! Kleintierpraxis 46:151–160