encephalitis

noun

en·​ceph·​a·​li·​tis in-ˌse-fə-ˈlī-təs How to pronounce encephalitis (audio)
plural encephalitides in-ˌse-fə-ˈli-tə-ˌdēz How to pronounce encephalitis (audio)
: 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.

encephalitic adjective

Examples of encephalitis in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Serious complications include pneumonia and encephalitis. Greg Norman, FOXNews.com, 9 July 2025 About 1 in 150 people who are infected develop a severe illness affecting the central nervous system, such as encephalitis — the inflammation of the brain — or meningitis — inflammation of the membranes that surround the brain and spinal cord. Brandi D. Addison, Austin American Statesman, 2 June 2025 Inflammation in the brain About one in 1,000 children who contract measles will also develop encephalitis, or inflammation of the brain tissue, which can result in permanent damage. Emily Baumgaertner Nunn, New York Times, 4 Apr. 2025 An orangutan at the Little Rock Zoo died earlier this week of encephalitis, the zoo said in a news release. Harley Walls, Arkansas Online, 28 June 2025 See All Example Sentences for encephalitis

Word History

First Known Use

1843, in the meaning defined above

Time Traveler
The first known use of encephalitis was in 1843

Browse Nearby Words

Cite this Entry

“Encephalitis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/encephalitis. Accessed 21 Jul. 2025.

Kids Definition

encephalitis

noun
en·​ceph·​a·​li·​tis in-ˌsef-ə-ˈlīt-əs How to pronounce encephalitis (audio)
(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 How to pronounce encephalitis (audio)
plural encephalitides -ˈlit-ə-ˌdēz How to pronounce encephalitis (audio)
: 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.

encephalitic adjective

More from Merriam-Webster on encephalitis

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