Viral Encephalitis

What is Viral Encephalitis?

Viral encephalitis refers to acute, diffuse inflammation of the brain caused by a viral infection. Other microorganisms such as bacteria and fungi can trigger encephalitis, but here we will focus on viral causes, the most common of which is the herpes simplex virus. It is a relatively rare pathology affecting mainly infants and the elderly.

Viral encephalitis can be confused for a non-infective encephalopathy as symptoms are similar, so a careful diagnosis is important.

This condition consists of an acute phase which may last 1 or 2 weeks.

Some of the viruses associated with viral encephalitis are:

• Enteroviruses
• Herpes simplex virus
• Epstein Barr virus
• Adenovirus
• Rubella
• Measles
• Varicella zoster virus (chicken pox)
• Cytomegalovirus
• Japanese encephalitis virus (encompasses dengue fever, yellow fever and West Nile disease)
• Murray Valley Encephalitis virus
• Kunjin virus

How do you catch it?

• Inhaling viral particles from the coughing/sneezing of an infected person
• Infected insects transmitting virus – eg mosquitos and ticks – as seen with Japanese encephalitis virus, which is spread by mosquitos
• Contaminated food or drink
• Touching an infected person or surface
• A dormant infection – like herpes simplex virus –  becoming active again
• Vaccination – note, this is extremely rare!
• A non-cancerous/cancerous growth elsewhere in the body causing the immune system to mistakenly attack the brain

What are the symptoms?

Symptoms of viral encephalitis initially resemble those of flu, but not always. We may also see similar symptoms to meningitis, including the rash that doesn’t fade when glass pressed against it.

Some initial symptoms may be:

• high temperature
• headache
• sensitivity to light (photophobia)
• general malaise
• stiff neck
• stiff back
• vomiting

In later stages of infection, we may also see:

• changes to personality
• confusion – this may fluctuate in cases of infective (viral) encephalitis, but not in non-infective
• memory loss (amnesia)
• seizures – these might be generalised (in multiple areas of the brain) or focal (only in one area)
• Low blood pressure (hypotension)
• Low blood oxygen (hypoxaemia)
• Bleeding in the brain (intracerebral haemorrhage)
• paralysis
• coma
• Brain damage
• Death (in 10% of cases)

How do we diagnose viral encephalitis?

Diagnosis of viral encephalitis will likely encompass multiple investigations.

A physical exam – we may see rash indicative of a particular virus such as measles or chickenpox

Blood tests – in cases of viral encephalitis leucocytosis (increased white blood cell count in the blood) is common, but not so in non-infective encephalopathies

Lumbar puncture – a sample of a patient’s cerebrospinal fluid (CSF) may show pleocytosis (increased white blood cell count in CSF) in viral encephalitis, but not in non-infective cases

Electroencephalogram (EEG) – electrodes placed on the scalp record the brain’s electrical activity. In viral encephalitis this may show a variety of abnormal patterns, including seizure activity.

We can also use imaging techniques such as:

Computed tomography (CT) scan – this may appear normal early on in the infection, or we may directly see one or both temporal lobes are less intense on an the image than other nearby areas.

Magnetic resonance imaging (MRI) – this scan may show inflammation that, coupled with symptom observation and other tests may be used to diagnose viral encephalitis. It may show different areas of inflammation depending on the virus an individual is infected with.

How is viral encephalitis treated?

Treatment primarily focuses on symptom relief, but may also involve antivirals if necessary/appropriate, most commonly intravenous acyclovir.

Symptom control may include:

• Pain relief
• fever control
• medication to prevent vomiting
• medication to reduce fever, such as paracetamol
• fluids to prevent dehydration – careful administration to avoid swelling of the brain (oedema) is important to account for.
• Immunoglobulin therapy – medication to control the immune system’s response
• medication to control seizures (anticonvulsants)
• medications to help reduce brain swelling – such as steroids

What are the side effects and long-term prognosis of viral encephalitis?

Most mild cases will resolve successfully with no long-term side effects.

Those who have suffered severe viral encephalitis may be left with memory loss, seizures, attention/concentration difficulties and personality changes, as well as persistent fatigue. In such cases, long term support could include behavioural and cognitive therapy to provide patients with the best quality of life and coping mechanisms.

Can we prevent viral encephalitis?

Although there is no specific vaccine, some vaccinations may offer protection against some causes of viral encephalitis:

MMR vaccine – this protects against measles, mumps, and rubella

Japanese encephalitis vaccine – this is offered if you are travelling in a risk area in Asia

Tick-born encephalitis vaccine – also offered for travelling in risk area of Europe or Asia

Summary

Viral encephalitis is inflammation of the brain as a result of a viral infection, such as the herpes simplex virus.

Early symptoms may resemble flu and/or meningitis

More severe symptoms include seizures, bleeding in the brain, low blood pressure, confusion and memory loss

Treatment may include antiviral medication but primarily focuses on the symptoms, for example anticonvulsants to control seizures or steroids to manage brain swelling

Most make a full recovery, but some are left with long term side effects that need further care and support

Vaccinations can prevent against viral infection, which may by extension reduce odds of developing viral encephalitis.

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