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.

encephalitic

in-ˌse-fə-ˈli-tik 

adjective

Examples of encephalitis in a Sentence

Recent Examples on the Web

Measles can cause pneumonia and encephalitis, erase immune memory and leave children more vulnerable to other infections, and, in rare cases, lead years later to a devastating fatal neurological disorder. — Demetre Daskalakis, STAT, 4 Sep. 2026

The virus can also cause numerous complications, including ear infections, diarrhea, lasting immune system damage, hospitalization, pneumonia, encephalitis, pregnancy problems and death. — Finch Walker, USA Today, 2 Sep. 2026

About 1 in 20 children who get measles will get pneumonia, and 1 in 1,000 will develop brain swelling, or encephalitis, which can lead to brain damage. — Brenda Goodman, CNN Money, 27 Aug. 2026

As many as 1 in every 20 children will get pneumonia, and 1 in every 1,000 children will get encephalitis, a swelling of the brain. — Arthur Jones Ii, ABC News, 27 Aug. 2026

Word History

First Known Use

1843, in the meaning defined above

Phrases Containing encephalitis

• Eastern equine encephalitis
• equine encephalitis
• Powassan encephalitis
• Saint Louis encephalitis
• St. Louis encephalitis
• Venezuelan equine encephalitis
• Western equine encephalitis
• West Nile encephalitis

Rhymes for encephalitis

• alveolitis
• bronchiolitis
• caenorhabditis
• cholecystitis
• endometritis
• endophthalmitis
• folliculitis
• periostitis
• peritonitis
• polyneuritis
• thrombophlebitis
• adenitis

Kids 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.

encephalitic

-ˈlit-ik 

adjective