Viral Encephalitis

What happens in viral encephalitis

Viruses can reach the brain through the bloodstream, along nerves (as with herpes simplex and rabies), or after reactivation of a virus lying dormant in nerves. The brain becomes inflamed and swollen, disrupting function. Specific viruses tend to target particular areas: herpes simplex affects the temporal lobes (memory, language and behavior), while West Nile can affect movement areas.

Encephalitis vs meningitis: meningitis is inflammation of the membranes covering the brain and spinal cord, causing headache, fever and stiff neck with normal thinking. Encephalitis affects the brain tissue itself, causing confusion, behavior change or seizures. The two often overlap (meningoencephalitis).

Causes

Autoimmune encephalitis, such as anti-NMDA receptor encephalitis, can mimic viral encephalitis and sometimes follows HSV encephalitis.

Symptoms

• fever and headache
• confusion, disorientation and agitation
• personality or behavior changes, hallucinations
• memory problems
• drowsiness, reduced consciousness or coma
• seizures
• weakness, speech difficulties, abnormal movements
• sensitivity to light and stiff neck if meninges are involved
• in babies: fever, irritability, poor feeding, vomiting, bulging fontanelle, seizures

Diagnosis

• MRI of the brain: shows inflammation; temporal lobe changes suggest herpes
• lumbar puncture: spinal fluid typically shows increased white cells and protein; PCR detects HSV, VZV, enteroviruses and others
• blood tests and antibody tests for arboviruses
• EEG: detects seizure activity and brain dysfunction
• testing for autoimmune antibodies if infection tests are negative
• CT scan before lumbar puncture in some cases

Treatment

• IV acyclovir is started immediately when encephalitis is suspected, without waiting for test results, and continued for 14 to 21 days if HSV is confirmed.
• Supportive care: fluids, fever control, nutrition, breathing support if needed, often in intensive care.
• Seizure control with anti-seizure medicines.
• Management of brain swelling.
• Specific antivirals for some other viruses (for example ganciclovir for CMV in immunocompromised people).
• Immunotherapy if autoimmune encephalitis is diagnosed.

Recovery and complications

Outcomes vary widely by cause, age and speed of treatment. Many people recover fully, especially with milder viruses. Others have lasting problems:

• memory loss and concentration difficulties
• personality and mood changes, depression and anxiety
• epilepsy
• speech and language problems
• weakness and coordination problems
• fatigue

Rehabilitation, including neuropsychology, speech, occupational and physical therapy, helps recovery, which can continue for months to years.

Prevention

• vaccination against measles, mumps, chickenpox, Japanese encephalitis (for travelers), tick-borne encephalitis (where available) and rabies (for high-risk people)
• mosquito and tick bite prevention: repellents, long clothing, avoiding dusk and dawn exposure
• prompt rabies post-exposure treatment after animal bites

Frequently asked questions

What are the first symptoms of viral encephalitis?

It often starts like the flu, with fever, headache and tiredness. Within hours to days, confusion, behavior changes, drowsiness, seizures or weakness can develop. These neurological symptoms with fever need emergency care.

What is the most common cause of viral encephalitis?

Herpes simplex virus is the most common identified cause of severe sporadic viral encephalitis. Enteroviruses and mosquito-borne viruses such as West Nile cause many seasonal cases.

Is viral encephalitis contagious?

The encephalitis itself is not passed between people, but some of the viruses that cause it are contagious, such as enteroviruses, measles and chickenpox. Mosquito- and tick-borne viruses are not spread person to person.

Can you fully recover from encephalitis?

Many people recover fully, especially with early treatment. Others are left with problems such as memory loss, seizures or personality changes. Rehabilitation helps, and improvement can continue for a long time.