Encephalitis

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/12/2026Status: primary verified

What is encephalitis? Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke , or even death. What causes encephalitis? There are different types of encephalitis, based on what the cause is. The two main types are infectious encephalitis and autoimmune encephalitis. Infectious encephalitis is usually caused by a virus . In fact, viruses are the most common cause of encephalitis. Some of the different viruses that cause it include: Herpes viruses, including herpes simplex (HSV), the Epstein-Barr virus (which causes infectious mononucleosis ) and the varicella-zoster virus (which causes chickenpox ). Viruses you can get if you are bitten by an infected tick , such as tick-borne encephalitis (TBE virus) and Powassan virus. Viruses you can get if you are bitten by an infected mosquito , such as eastern equine encephalitis virus, West Nile virus , and La Crosse virus. Enteroviruses, which are a common group of viruses that mostly cause mild illness or respiratory infection. These infections usually happen in the summer and fall. Bacteria , fungi , and parasites can also cause infectious encephalitis. But this is not common. Autoimmune encephalitis happens when your immune system mistakenly attacks healthy brain cells. It can be triggered by conditions such as certain cancers, benign tumors , and infections. Sometimes the cause is not known. Who is more likely to get encephalitis? Anyone can get encephalitis, but you are more likely to get it if you: Have a weakened immune system, for example from having HIV or taking certain medicines. These could include medicines taken after an organ transplant , certain chemotherapy medicines, and specialized treatments for certain autoimmune diseases . Are a young child or older adult. Live in areas where there are ticks and

Educational only

This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.