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
Besides being nuisances, many types carry diseases including West Nile virus, encephalitis, and canine heartworm.
—
Arricca Elin Sansone, Southern Living, 18 June 2026
In severe cases, UCHealth says the virus can cause serious complications such as encephalitis or meningitis.
—Christa Swanson, CBS News, 17 June 2026
In some cases, Powassan virus can cause severe disease, including encephalitis, an infection of the brain, or meningitis, an infection of membranes around the brain and spinal cord.
—Emily Vetter, USA Today, 16 June 2026
More serious outcomes can include pneumonia, encephalitis — or swelling of the brain — and, in rare cases, death, according to the CDC.
—Sacbee.com, 9 June 2026
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Arricca Elin Sansone, Southern Living, 18 June 2026
In severe cases, UCHealth says the virus can cause serious complications such as encephalitis or meningitis.
—Christa Swanson, CBS News, 17 June 2026
In some cases, Powassan virus can cause severe disease, including encephalitis, an infection of the brain, or meningitis, an infection of membranes around the brain and spinal cord.
—Emily Vetter, USA Today, 16 June 2026
More serious outcomes can include pneumonia, encephalitis — or swelling of the brain — and, in rare cases, death, according to the CDC.
—Sacbee.com, 9 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 19 Jun. 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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