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Encephalitis
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Brain Nerves

Encephalitis

Encephalitis is the inflammation of the brain caused by an immune system response to an infection or medical condition, potentially leading to severe complications like brain damage or death.

Causes

The two main types of encephalitis are categorized by their cause:

  • Infectious encephalitis: Usually caused by viruses, including herpes viruses (HSV, Epstein-Barr, varicella-zoster), tick-borne viruses (TBE, Powassan), mosquito-borne viruses (eastern equine, West Nile, La Crosse), and enteroviruses. Bacteria, fungi, and parasites can also cause this type, though it is less common.
  • Autoimmune encephalitis: Occurs when the immune system mistakenly attacks healthy brain cells. This can be triggered by certain cancers, benign tumors, infections, or unknown factors.

Risk Factors

While anyone can develop encephalitis, you are at higher risk if you:

  • Have a weakened immune system due to HIV, organ transplant medications, chemotherapy, or treatments for autoimmune diseases.
  • Are a young child or an older adult.
  • Live in areas populated by ticks and mosquitoes that carry relevant viruses.

Symptoms

Symptoms vary in severity; many people experience no symptoms at all, while others may have mild flu-like signs such as fever, fatigue, headache, or body aches. Serious cases may present with:

  • Severe headache and stiff neck
  • Vomiting and seizures
  • Behavior changes and drowsiness
  • Muscle weakness or partial paralysis
  • Coma

In infants, symptoms may include fever, lethargy, poor feeding, vomiting, body stiffness, unusual irritability, or a bulging fontanel.

Diagnosis

Health care providers diagnose encephalitis through:

  • Physical and neurologic exams
  • Medical history review
  • Imaging tests (CT scan or MRI)
  • EEG (electroencephalography) to measure brain activity
  • Blood and cerebrospinal fluid (CSF) tests

Treatment and Management

Most patients require hospitalization. Treatments may include antiviral medicines, antibiotics, or corticosteroids. In cases where no specific medicine exists, care focuses on rest, nutrition, and fluids. Post-illness recovery may involve physical, speech, or occupational therapy.

Prevention

Steps to prevent infectious encephalitis include:

  • Practicing good hygiene, such as frequent handwashing.
  • Avoiding the sharing of food, drinks, or utensils.
  • Staying up to date on relevant vaccines.
  • Preventing mosquito and tick bites by using EPA-registered insect repellent (such as DEET), wearing protective clothing, and treating gear with 0.5% permethrin.

Frequently Asked Questions

Infectious encephalitis, particularly from herpes simplex virus, requires immediate intravenous antiviral therapy to stop viral replication, often starting within hours of diagnosis to prevent permanent damage. Autoimmune encephalitis, however, requires immunotherapy such as high-dose steroids, IVIG, or plasmapheresis to suppress the immune system's attack on the brain. Recovery from autoimmune cases can take months to years and often involves long-term rehabilitation for cognitive and motor deficits, whereas infectious cases may resolve faster if caught early but carry a higher risk of acute complications like seizures during the initial phase.
Full recovery is possible, especially if the condition is diagnosed and treated early, but it is not guaranteed. The most common long-term complications include chronic fatigue, memory loss, difficulty with concentration, and personality or behavioral changes. Some patients may experience residual seizure disorders or motor deficits such as weakness on one side of the body. The extent of recovery depends heavily on the specific virus or antibody involved, the duration of the illness before treatment, and the age of the patient.
Prevention focuses on vector avoidance. In tick-endemic areas, individuals should wear long sleeves and pants, use insect repellent containing DEET or permethrin on clothing, and perform thorough tick checks after spending time in grassy or wooded areas. For mosquito-borne risks, staying indoors during peak mosquito activity (dawn and dusk), using window screens, and eliminating standing water around the home are critical. Vaccination is available for specific viruses like Japanese encephalitis or tick-borne encephalitis, but only for those traveling to or living in specific high-risk regions.
While fever and headache are common to all three, encephalitis is distinguished by the rapid onset of neurological changes. Immediate red flags include new-onset confusion or disorientation, difficulty waking up, stiff neck accompanied by a severe headache, or any seizure activity. If a patient with a fever becomes suddenly irritable, hallucinates, or loses the ability to speak clearly, this suggests brain inflammation rather than a simple viral illness and requires immediate medical evaluation.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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