ISSN 2398-2969      

Tick-borne encephalitis (TBE)

icanis
Contributor(s):

Ian Wright

Sue Paterson


Introduction

  • Cause: tick-borne encephalitis virus (TBEV) from the Flavivrus genus of the Flaviviridae family.
  • Signs: ataxia, proprioceptive deficits, seizures, tremor, paresis, paralysis and cranial nerve deficits. Neurological signs are often progressive and fatal.
  • Diagnosis: serology, immunohistology.
  • Treatment: supportive.
  • Prognosis: variable in human cases, very guarded to grave in dogs.

Pathogenesis

Etiology

  • Caused by TBEV. There are three subtypes of TBEV currently recognized (European, Siberian, and Far Eastern), although Baikalian and Himalayan subtypes have also recently been proposed.
  • The far Eastern subtype is more pathogenic in people with a higher mortality rate (25-30% compared to 1-5% mortality in the European strain). Although disease is rare in dogs, when it develops it is often fatal, whichever strain is involved.

Predisposing factors

General

  • Immune status of the dog.
  • The amount of time spent exposed to ticks in endemic countries.
  • Stress.
  • Immunosuppression.
  • Concurrent disease.

Specific

  • Exposure to infected ticks (primarily Ixodes ricinus Ixodes ricinus in Western and Central Europe, Ixodes persulcatus, in Central and Eastern Europe and Ixodes ovatus in Japan but also less commonly Dermacentor reticulatus Dermacentor reticulatus). 
  • Alimentary transmission has been reported from the consumption of unpasteurized milk and milk products from livestock.

Pathophysiology

  • Viral infection leads to severe encephalitis Encephalitis/ meningoencephalitis in the absence of gross visceral changes.
  • Large areas of brain affected by inflammation with infiltrates of lymphocytes, histiocytes and plasma cells.
  • Pyrexia Pyrexia: overview and altered behavior caused by inflammation in the thalamus and cerebral cortex.
  • Proprioceptive deficits caused by inflammation in the mesencephalon.
  • Motor neuron deficits caused by spinal cord inflammation.
  • Severe neck pain caused by meningitis Meningitis.
  • Head tilt, nystagmus and strabismus caused by inflammation of the brainstem.
  • The pathological changes are similar in humans and dogs.
     

Timecourse

  • Peracute lethal 3-7 days. 
  • Acute 1-3 weeks. 
  • Chronic subclinical - months and milk products from livestock.

Epidemiology

  • TBEV is a seasonal disease which depends on the climate related activity of the ticks.
  • Rodents act as reservoir hosts capable of maintaining the pathogen once it has moved to a new area.
  • Larger wild animals such as deer are not considered to be competent hosts for virus transmission but serve as reproductive and transport hosts for infected ticks, allowing maintenance of tick populations and geographical spread of TBEV.
  • Migratory birds are also likely to play a significant role in carrying infected ticks over large distances.
  • Within the tick population, the virus is maintained via the transstadial route and possibly to a lesser extent, via transovarial transmission to the next developmental stage of the tick's life cycle.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Holding M, Dowall S D, Medlock J M, Carter D P, Pullan S T et al (2020) Tick-Borne Encephalitis Virus, United Kingdom. Emerg Infect Dis 26, 90-96 PubMed.
  • Dai X, Shang G, Lu S, Yang J & Xu J (2018) A new subtype of eastern tick-borne encephalitis virus discovered in Qinghai-Tibet Plateau, China. Emerging Microbes and Infections 7, 74 PubMed Full Article.
  • Jahfari S, de Vries A, Rijks J M, Van Gucht S, Vennema H, Sprong H et al (2017) Tick-borne encephalitis virus in ticks and roe deer, the Netherlands. Emerg Infect Dis 23, 1028-1030 PubMed.
  • Imhoff M, Hagedorn P, Schulze Y, Hellenbrand W, Pfeffer M et al (2015) Review: Sentinels of tick-borne encephalitis risk. Ticks and Tick Borne Diseases 6, 592-600 PubMed.
  • Pfeffer M & Dobler G (2011) Tick-borne encephalitis virus in dogs – is this an issue? Parasites & Vectors 4, 59 PubMed Full Article.
  • Lindquist L & Vapalahti O (2008) Tick-borne encephalitis. Lancet 371, 1861-1871 PubMed.
  • Gritsun T S, Nuttall P A & Gould E A (2003) Tick-borne flaviviruses. Adv Virus Res 61, 317-317 PubMed.

Organisation(s)

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