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
Measles can result in serious complications, including pneumonia, encephalitis and death.
—
Eve Chen, USA Today, 3 Feb. 2026
The virus can lead to severe symptoms, including disorientation, drowsiness, seizures or encephalitis, which is inflammation of the brain.
—Mary Kekatos, ABC News, 29 Jan. 2026
Vaccines eradicated smallpox and were thought to have done so with polio and measles, which can cause encephalitis and other potentially fatal complications.
—Orlando Sentinel, The Orlando Sentinel, 28 Jan. 2026
There are serious complications of pneumonia (1 in 20), encephalitis (brain swelling) in 1/1,000, deafness in many and deaths in 1-3/1,000.
—Judy Stone, Forbes.com, 24 Jan. 2026
See All Example Sentences for encephalitis
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Eve Chen, USA Today, 3 Feb. 2026
The virus can lead to severe symptoms, including disorientation, drowsiness, seizures or encephalitis, which is inflammation of the brain.
—Mary Kekatos, ABC News, 29 Jan. 2026
Vaccines eradicated smallpox and were thought to have done so with polio and measles, which can cause encephalitis and other potentially fatal complications.
—Orlando Sentinel, The Orlando Sentinel, 28 Jan. 2026
There are serious complications of pneumonia (1 in 20), encephalitis (brain swelling) in 1/1,000, deafness in many and deaths in 1-3/1,000.
—Judy Stone, Forbes.com, 24 Jan. 2026
See All Example Sentences for encephalitis
Cite this Entry
“Encephalitis.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/encephalitis. Accessed 9 Feb. 2026.
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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