encephalitis
noun
en·ceph·a·li·tis
in-ˌse-fə-ˈlī-təs 
plural encephalitides
in-ˌse-fə-ˈli-tə-ˌdēz
: inflammation of the brain that is caused especially by infection with a virus (such as herpes simplex or West Nile virus) or less commonly by bacterial or fungal infection or autoimmune reaction
Note: Encephalitis may be asymptomatic or present with mild to severe symptoms (such as fever, headache, confusion, seizures, or loss of consciousness) sometimes progressing to coma or death.
Examples of encephalitis in a Sentence
Recent Examples on the Web
Beckett Wear temporarily lost his ability to walk after two bouts of acute necrotizing encephalitis.
—
Erika Edwards, NBC news, 25 Sep. 2025
Along with a high fever, cough, and runny nose, measles also carries a risk of pneumonia and encephalitis (swelling of the brain), which can cause hearing loss, cognitive disabilities and death.
—Cara Lynn Shultz, PEOPLE, 25 Sep. 2025
In rare serious cases, the virus invades the nervous system, causing meningitis, encephalitis (swelling of the brain), paralysis or death.
—Khloe Quill, FOXNews.com, 15 Sep. 2025
Measles can also cause encephalitis, a faster-occurring brain inflammation, in one in every 1,000 people who are infected because the virus causes the immune system to attack a protein produced by certain brain cells.
—Andrea Thompson, Scientific American, 12 Sep. 2025
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Erika Edwards, NBC news, 25 Sep. 2025
Along with a high fever, cough, and runny nose, measles also carries a risk of pneumonia and encephalitis (swelling of the brain), which can cause hearing loss, cognitive disabilities and death.
—Cara Lynn Shultz, PEOPLE, 25 Sep. 2025
In rare serious cases, the virus invades the nervous system, causing meningitis, encephalitis (swelling of the brain), paralysis or death.
—Khloe Quill, FOXNews.com, 15 Sep. 2025
Measles can also cause encephalitis, a faster-occurring brain inflammation, in one in every 1,000 people who are infected because the virus causes the immune system to attack a protein produced by certain brain cells.
—Andrea Thompson, Scientific American, 12 Sep. 2025
See All Example Sentences for encephalitis
Cite this Entry
“Encephalitis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/encephalitis. Accessed 29 Sep. 2025.
Copy CitationKids Definition
encephalitis
noun
en·ceph·a·li·tis
in-ˌsef-ə-ˈlīt-əs
(ˌ)en-
: inflammation of the brain
also
: a disease marked by encephalitis
Medical Definition
encephalitis
noun
en·ceph·a·li·tis
in-ˌsef-ə-ˈlīt-əs
plural encephalitides
-ˈlit-ə-ˌdēz
: inflammation of the brain that is caused especially by infection with a virus (such as herpes simplex, varicella zoster, or West Nile virus) or less commonly by bacterial or fungal infection or autoimmune reaction
Note: Encephalitis may be asymptomatic or present with mild to severe symptoms (such as fever, headache, confusion, seizures, or loss of consciousness) sometimes progressing to coma or death.
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