[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Central nervous system](https://durgical.com/en/general-pathology/areas/cns/) › Viral encephalitis: the shared pattern

# Viral encephalitis: the shared pattern

- Lesion

Viruses that infect the brain leave a common footprint of lymphocytes around vessels and microglial clusters, plus clues to each virus.

Updated Nov 12, 2026

## Key points

- Shared pattern: perivascular and parenchymal lymphocytes, microglial nodules, neuronophagia, sometimes inclusions.
- Arboviruses: West Nile, equine encephalitis viruses, Japanese encephalitis, St Louis; Zika and dengue can involve the nervous system in the Americas.
- Tropism gives the clinical picture: temporal lobes (HSV-1), anterior horns (polio), brainstem and limbic system (rabies), ependyma (CMV).
- SSPE: years after measles in childhood, progressive cognitive decline, myoclonus and death; inclusions in neurons and oligodendrocytes and very high measles antibodies in CSF.
- Measles vaccination prevents SSPE.

## What it is

Viral encephalitis is infection of the brain parenchyma, usually with meningitis. Most viruses share the same histology: lymphocytes cuffing blood vessels, microglial nodules and neuronophagia. Particular viruses add tropism for certain cells or regions and their own inclusions. Mosquito-borne arboviruses cause outbreaks; measles can persist for years and cause subacute sclerosing panencephalitis, a fatal late complication.

## Structure

- Arboviral encephalitis: widespread perivascular lymphocytes with neutrophils early, microglial nodules and focal necrosis, mostly in grey matter.
- SSPE: grey and white matter gliosis, neuronal loss, nuclear and cytoplasmic measles inclusions, neurofibrillary tangles in long cases.
- Some infections trigger an immune reaction rather than direct infection, as in post-infectious encephalomyelitis and autoimmune encephalitis.

## Step by step

- A virus enters by mosquito bite, the gut, the respiratory tract or a nerve ending.
- It reaches the brain by the blood or by travelling along nerves.
- It infects neurons or glia according to its receptors and tropism.
- T cells and microglia gather around infected cells and vessels.
- Infected neurons are destroyed (neuronophagia); edema and necrosis follow in severe cases.

## Viral encephalitis clues

| Virus | Favoured target | Distinctive finding |
| --- | --- | --- |
| [Herpes simplex virus type 1](https://durgical.com/en/conditions/viral-encephalitis/) | Temporal and orbitofrontal lobes | Hemorrhagic necrosis, Cowdry A inclusions |
| [Poliovirus](https://durgical.com/en/conditions/poliomyelitis-and-acute-flaccid-paralysis/) | Anterior horn motor neurons | Flaccid asymmetric paralysis |
| [Rabies](https://durgical.com/en/conditions/rabies/) | Brainstem, limbic system, Purkinje cells | Negri bodies |
| [Cytomegalovirus](https://durgical.com/en/conditions/cytomegalovirus-infection/) | Ependyma and subependymal region | Owl-eye inclusions, periventricular necrosis |
| [JC virus](https://durgical.com/en/conditions/hiv-infection-and-aids/) | Oligodendrocytes | Demyelination (PML) |
| [Measles (persistent)](https://durgical.com/en/conditions/measles/) | Neurons and oligodendrocytes | SSPE, years after infection |
| West Nile and other arboviruses | Grey matter, including brainstem and anterior horns | Outbreaks, flaccid weakness possible |

## Clinical notes

- Fever, headache, confusion, seizures and focal signs; MRI, CSF PCR and serology identify the virus.
- Autoimmune encephalitis (for example anti-NMDA receptor) can follow HSV encephalitis and mimics viral disease.

## Memory aid

Cuffs, clusters and cannibalised neurons: the shared signature of viral encephalitis.

## Test yourself

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

## What are the three shared histologic features of viral encephalitis?

Perivascular lymphocytic cuffs, microglial nodules and neuronophagia.

## What is subacute sclerosing panencephalitis?

A progressive fatal encephalitis years after childhood measles, caused by persistent defective measles virus in the brain.

## Which virus targets oligodendrocytes and causes demyelination?

JC polyomavirus, the cause of progressive multifocal leukoencephalopathy.

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## Connections

## Related 6

- [Herpesvirus encephalitis](https://durgical.com/en/general-pathology/herpesvirus-encephalitis/)
- [Poliomyelitis and rabies](https://durgical.com/en/general-pathology/poliomyelitis-and-rabies/)
- [HIV in the brain and PML](https://durgical.com/en/general-pathology/hiv-in-the-brain-and-pml/)
- [How brain cells react to injury](https://durgical.com/en/general-pathology/how-brain-cells-react-to-injury/)
- [Other demyelinating diseases](https://durgical.com/en/general-pathology/other-demyelinating-diseases/)
- [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/)

## Related conditions 6

- [Viral encephalitis (herpes simplex encephalitis)](https://durgical.com/en/conditions/viral-encephalitis/)
- [Viral (aseptic) meningitis](https://durgical.com/en/conditions/viral-meningitis/)
- [Measles](https://durgical.com/en/conditions/measles/)
- [Zika virus infection](https://durgical.com/en/conditions/zika-virus-infection/)
- [Dengue](https://durgical.com/en/conditions/dengue/)
- [Autoimmune encephalitis (including anti-NMDA receptor encephalitis)](https://durgical.com/en/conditions/autoimmune-encephalitis/)

## Microorganisms 6

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

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Encephalitis | MedlinePlus](https://medlineplus.gov/encephalitis.html) (MedlinePlus, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/viral-encephalitis-the-shared-pattern/