[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [RNA arboviruses](https://durgical.com/en/microbiology/groups/rna-arboviruses/) › Japanese, St. Louis and tick-borne encephalitis viruses

# 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 Nov 13, 2026

Also called: JEV, SLEV, TBEV, neurotropic flaviviruses

## Quick facts

**Type**
Virus · [RNA arboviruses](https://durgical.com/en/microbiology/groups/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

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- In Colombia
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Flaviviruses: enveloped positive-sense RNA, relatives of dengue and West Nile
- JE: Culex, pigs and wading birds, rural Asia; leading vaccine-preventable encephalitis in Asia
- TBE: Ixodes ticks or raw milk; biphasic course; inactivated vaccine
- SLE: Culex and birds in the Americas; worse in older adults; no vaccine
- Diagnosis by IgM in CSF; beware cross-reactions with other flaviviruses

## 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

- Viral encephalitis (Japanese, St. Louis, tick-borne) [Viral encephalitis (herpes simplex encephalitis) →](https://durgical.com/en/conditions/viral-encephalitis/)
- Aseptic meningitis and meningoencephalitis [Viral (aseptic) meningitis →](https://durgical.com/en/conditions/viral-meningitis/)
- Acute flaccid paralysis (poliomyelitis-like) in JE and TBE

## 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.

## In Colombia

Japanese and tick-borne encephalitis do not occur in the Americas; they concern travellers to Asia and Europe. St. Louis encephalitis virus does circulate in the Americas, and its IgM cross-reacts with dengue, Zika and yellow fever, so a positive flavivirus serology in Colombia needs careful interpretation.

## Memory aid

"Pigs and rice: JE; Ticks and milk: TBE; Birds of St. Louis: SLE" - three hosts, three encephalitides, one virus family.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/japanese-st-louis-and-tick-borne-encephalitis-viruses/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

## Connections

## Related 5

- [West Nile virus](https://durgical.com/en/microbiology/west-nile-virus/)
- [Dengue virus](https://durgical.com/en/microbiology/dengue-virus/)
- [Yellow fever virus](https://durgical.com/en/microbiology/yellow-fever-virus/)
- [Zika virus](https://durgical.com/en/microbiology/zika-virus/)
- [Equine encephalitis viruses and Mayaro virus](https://durgical.com/en/microbiology/equine-encephalitis-viruses-and-mayaro-virus/)

## Related conditions 2

- [Viral encephalitis (herpes simplex encephalitis)](https://durgical.com/en/conditions/viral-encephalitis/)
- [Viral (aseptic) meningitis](https://durgical.com/en/conditions/viral-meningitis/)

[← Back to the group: RNA arboviruses](https://durgical.com/en/microbiology/groups/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](https://www.who.int/news-room/fact-sheets/detail/japanese-encephalitis) (World Health Organization (WHO), 2024); [Factsheet about tick-borne encephalitis (TBE)](https://www.ecdc.europa.eu/en/tick-borne-encephalitis/facts/factsheet) (European Centre for Disease Prevention and Control (ECDC), 2024); [About St. Louis Encephalitis Virus](https://www.cdc.gov/sle/about/index.html) (CDC, 2024); [About Tick-borne Encephalitis Virus](https://www.cdc.gov/tick-borne-encephalitis/about/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/japanese-st-louis-and-tick-borne-encephalitis-viruses/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/japanese-st-louis-and-tick-borne-encephalitis-viruses/