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Japanese, St. Louis and tick-borne encephalitis viruses

  • Virus
  • Enveloped
  • Exam priority: medium

Flaviviruses spread by mosquitoes or ticks. Most infections pass unnoticed, but a few cause brain inflammation; vaccines exist for two of them.

Updated

Also called: JEV, SLEV, TBEV, neurotropic flaviviruses

Quick facts

Type
Virus · RNA arboviruses
Gram / shape
Spherical
Spread
Japanese encephalitis · St · Tick-borne encephalitis
Causes
Viral encephalitis · Aseptic meningitis
Treatment
There is no specific antiviral for any of the three

At a glance

Shape
Spherical, icosahedral
Genome
Single-stranded, positive-sense RNA
Envelope
Enveloped
Family
Flaviviridae, genus Orthoflavivirus
Size
About 50 nm

Morphology

  • Envelope protein E mediates attachment and fusion and is the main target of neutralizing antibodies
  • Close relatives of West Nile, dengue, Zika and yellow fever viruses, which explains antibody cross-reactions
  • TBEV has three subtypes: European, Siberian and Far Eastern

Transmission

  • Japanese encephalitis: Culex mosquitoes (mainly Culex tritaeniorhynchus) in rural Asia and the Western Pacific, around rice fields
  • St. Louis encephalitis: Culex mosquitoes in the Americas, from the United States to South America
  • Tick-borne encephalitis: Ixodes ticks in Europe and northern Asia; also raw milk or cheese from infected goats, sheep or cows
  • Humans are dead-end hosts for JEV and SLEV: their viraemia is too low to infect mosquitoes

Reservoir: Pigs and wading birds (JEV amplifiers); Wild birds (SLEV); Small rodents and ticks themselves (TBEV)

Vector: Culex mosquitoes (JEV, SLEV); Ixodes ricinus and Ixodes persulcatus ticks (TBEV)

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Virulence factors

  • After a skin bite the virus multiplies in lymph nodes, causes viraemia and can cross into the CNS
  • Neurons of the thalamus, basal ganglia, brainstem and spinal cord are targets, giving movement disorders and flaccid paralysis
  • Risk of severe disease rises with age (SLEV, TBEV); JE mainly affects children in endemic areas

Diseases it causes

Clinical picture

  • Most infections are asymptomatic; for JE about 1 in 250 becomes severe
  • JE: fever, headache, vomiting, then altered consciousness, seizures (especially in children) and parkinsonian features; up to 30% die and many survivors keep sequelae
  • SLE: fever and headache, meningitis or encephalitis, more severe in older adults
  • TBE: often biphasic (flu-like phase, symptom-free interval, then meningitis or encephalitis); case fatality highest with the Far Eastern subtype

Diagnosis

  • IgM capture ELISA on CSF (preferred) and serum; repeat on a convalescent sample if negative
  • Cross-reactivity with dengue, Zika, West Nile and yellow fever (including vaccine) is common; neutralization tests confirm
  • CSF: lymphocytic pleocytosis, raised protein, normal glucose
  • MRI in JE may show thalamic and basal ganglia lesions; RT-PCR is positive only early

Treatment

There is no specific antiviral for any of the three: care is supportive (airway, seizure control, intracranial pressure and fluids) with rehabilitation for survivors.

Drug class only; doses and regimens are set by the clinician from the current guideline.

Prevention

  • Avoid mosquito bites (repellent, long clothing, nets) in rural Asia and during Culex activity
  • Avoid tick bites, check the skin after outdoor activity and avoid unpasteurized dairy in TBE areas
  • Japanese encephalitis vaccines (inactivated Vero cell, live attenuated and live chimeric) for endemic countries and long-stay travellers
  • Inactivated TBE vaccine in endemic European and Asian countries; no vaccine for SLE

Vaccine: Vaccines exist for Japanese encephalitis and tick-borne encephalitis and are given in endemic countries and to some travellers; there is none for St. Louis encephalitis. None is in Colombia's PAI schedule.

Test yourself

Think of the answer, then tap the question to see it.

Which animals amplify Japanese encephalitis virus?

Pigs and wading birds; humans are dead-end hosts.

Besides tick bites, how can tick-borne encephalitis be acquired?

By eating or drinking unpasteurized milk or cheese from infected goats, sheep or cows.

What is the preferred test for Japanese encephalitis?

JEV-specific IgM capture ELISA, preferably on CSF, with a convalescent sample if the first is negative.

Which of the three viruses is found in the Americas?

St. Louis encephalitis virus, carried by Culex mosquitoes and birds.

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Connections

← Back to the group: RNA arboviruses

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Japanese encephalitis (World Health Organization (WHO), 2024); Factsheet about tick-borne encephalitis (TBE) (European Centre for Disease Prevention and Control (ECDC), 2024); About St. Louis Encephalitis Virus (CDC, 2024); About Tick-borne Encephalitis Virus (CDC, 2024).

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