Encephalitis is inflammation of the brain. It is most often caused by a viral infection, although autoimmune reactions and other causes are possible. Encephalitis can become serious quickly and requires prompt medical assessment.
Possible symptoms
- Fever and headache
- Confusion, unusual behavior or reduced alertness
- Seizures
- Weakness, difficulty speaking or movement problems
- Sensitivity to light
- Loss of consciousness in severe cases
Causes
Several viruses can cause encephalitis, including herpes simplex virus and some mosquito- or tick-borne viruses. In autoimmune encephalitis, the immune system mistakenly targets proteins in the brain.
Diagnosis and treatment
Tests may include brain imaging, lumbar puncture, blood tests and EEG. Treatment depends on the cause. Suspected herpes simplex encephalitis is treated urgently with intravenous antiviral medicine. Other patients may need immune-directed treatment, seizure treatment, intensive supportive care or rehabilitation.
When to seek emergency help
Seek emergency medical care for new confusion, seizures, reduced consciousness, severe headache with neurological symptoms, sudden weakness or rapidly worsening illness. Encephalitis is not a condition to manage with home treatment alone.
Related topics
Sources and further reading
Last reviewed: 4 September 2026. This page provides general health information and does not replace individual medical assessment or treatment.