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
In these cases, the virus affects the brain or nervous system and can cause encephalitis or meningitis, which can result in an infection of the brain or surrounding tissue, according to the CDC.
—
Karen Garcia,
Los Angeles Times,
30 June 2026
In severe cases, the virus affects the central nervous system, causing encephalitis (inflammation of the brain) or meningitis (inflammation of the membrane around the brain and spinal cords).
—
Cara Lynn Shultz,
PEOPLE,
29 June 2026
Though rare — there are up to 6,000 cases in the UK each year — encephalitis is often life-threatening.
—
George Ramsay,
New York Times,
23 June 2026
The rare but increasingly prevalent Powassan virus, spread mainly by the black-legged tick, can reach the brain and cause encephalitis.
—
Kate Wong,
Scientific American,
22 June 2026
See All Example Sentences for encephalitis
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Karen Garcia,
Los Angeles Times,
30 June 2026
In severe cases, the virus affects the central nervous system, causing encephalitis (inflammation of the brain) or meningitis (inflammation of the membrane around the brain and spinal cords).
—
Cara Lynn Shultz,
PEOPLE,
29 June 2026
Though rare — there are up to 6,000 cases in the UK each year — encephalitis is often life-threatening.
—
George Ramsay,
New York Times,
23 June 2026
The rare but increasingly prevalent Powassan virus, spread mainly by the black-legged tick, can reach the brain and cause encephalitis.
—
Kate Wong,
Scientific American,
22 June 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 3 Jul. 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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