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What is Encephalitis?

Encephalitis means "inflammation of the brain," but it usually refers to brain inflammation caused by a virus. This severe and potentially life-threatening disease is rare.

Mosquitoes can transmit the viruses for several types of encephalitis, including West Nile encephalitis, St. Louis encephalitis, and Western Equine encephalitis.

One of the most dangerous and most common causes of encephalitis is the herpes simplex virus (HSV). HSV is the same virus that causes cold sores around the mouth, but when it attacks the brain it may occasionally be fatal. Herpes simplex encephalitis is caused by the herpes simplex virus that manifests in oral cold sores or genital sores.

When this triggers brain inflammation, which occurs in 10% of cases of encephalitis (2 cases per million people), half of all untreated patients die (1 case per million people). Brain damage, partial paralysis, seizures, hallucinations and an altered state of consciousness are all common symptoms. HSE can be passed from mother to child during birth in rare cases, where symptoms include lethargy, tremors, irritability, seizures and poor feeding in the first two weeks after birth.

Patients with encephalitis suffer from fever, headache and photophobia with weakness and seizures also common. Less commonly, stiffness of the neck can occur with rare cases of patients also suffering from stiffness of the limbs, slowness in movement and clumsiness depending on which specific part of the brain is involved. The symptoms of encephalitis are caused by the brain's defense mechanisms activating to get rid of the infection.

Encephalitis takes two forms, categorized by the two ways that viruses can infect your brain:

Primary encephalitis.

This occurs when a virus directly invades your brain and spinal cord. It can happen to people at any time of the year (sporadic encephalitis), or it can be part of an outbreak (epidemic encephalitis).

Secondary (post-infectious) encephalitis.

This form occurs when a virus first infects another part of your body and secondarily enters your brain.

The primary form of the disease is more serious, while the secondary form is more common. But because of the milder nature of secondary encephalitis, doctors actually see more cases of primary encephalitis.

Signs and Symptoms

Milder forms of encephalitis can follow or accompany common childhood illnesses, including measles, mumps, chickenpox, rubella (German measles), and mononucleosis.

Symptoms in milder cases of encephalitis usually include:


loss of energy

a general sick feeling

poor appetite


In more severe cases of encephalitis, a person is more likely to experience high fever and any of a number of symptoms that relate to the central nervous system, including:

stiff neck



memory loss



severe headache

nausea and vomiting


personality changes

convulsions (seizures)

problems with speech or hearing

It's harder to detect some of these symptoms in infants, but important signs to look for include:


a full or bulging soft spot (fontanel)

crying that doesn't stop or that seems worse when an infant is picked up or handled in some way

body stiffness

For most forms of encephalitis, the acute phase of the illness (when symptoms are the most severe) usually lasts up to a week. Full recovery can take much longer, often several weeks or months.

See your doctor if you experience signs and symptoms of primary or secondary encephalitis because the course of the disease is unpredictable.

Seek immediate medical attention if your child has any of the following symptoms:

severe headache

inability to look at bright lights

double vision

difficulty walking

problems with speech

convulsions (seizures)

stiff neck

sudden personality changes

problems with memory

extreme drowsiness or lethargy

loss of consciousnes or hearing

difficulty moving an arm or leg

loss of sensation anywhere in the body

If your infant has any of the following symptoms, seek immediate medical care:

high fever or any fever higher than 100.4 Deg Fahrenheit (38 Deg Celsius) in infants younger than 3 months of age.

fullness or bulging in the soft spot

any stiffness

poor appetite or reduced feeding


crying that won't stop

floppiness or decreased tone


Treatment is usually symptomatic.

Reliably tested specific antiviral agents are available only for a few viral agents (e.g. acyclovir for herpes simplex virus) and are used with limited success for most infection except herpes simplex encephalitis.

In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important.

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