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
Some are left with the long-term consequences of encephalitis — inflammation of the brain that can lead to seizures, blindness, deafness and learning disabilities.
—
Erika Edwards, NBC news, 1 Mar. 2026
While no deaths have been reported, the state has reported severe complications from measles — including pneumonia and encephalitis, which can leave the patient deaf or with intellectual disability.
—Deidre McPhillips, CNN Money, 27 Feb. 2026
Measles is a potentially serious illness, with complications occurring in about 30% of infected individuals, including immune suppression, pneumonia, diarrhea, and encephalitis, which may be life-threatening.
—Rick Sobey, Boston Herald, 27 Feb. 2026
Measles is highly contagious and can cause pneumonia, encephalitis, and death, particularly in children.
—Jerome Adams, STAT, 27 Feb. 2026
See All Example Sentences for encephalitis
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Erika Edwards, NBC news, 1 Mar. 2026
While no deaths have been reported, the state has reported severe complications from measles — including pneumonia and encephalitis, which can leave the patient deaf or with intellectual disability.
—Deidre McPhillips, CNN Money, 27 Feb. 2026
Measles is a potentially serious illness, with complications occurring in about 30% of infected individuals, including immune suppression, pneumonia, diarrhea, and encephalitis, which may be life-threatening.
—Rick Sobey, Boston Herald, 27 Feb. 2026
Measles is highly contagious and can cause pneumonia, encephalitis, and death, particularly in children.
—Jerome Adams, STAT, 27 Feb. 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 5 Mar. 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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