encephalitis

American  

[en-sef-uh-lahy-tis] / ɛnˌsɛf əˈlaɪ tɪs /

noun

Pathology.

1. inflammation of the substance of the brain.

2. Also called encephalitis lethargica.  a form of this condition, caused by a filterable virus and characterized by apathy and abnormal sleepiness; sleeping sickness.

---

encephalitis British  

/ ˌɛnkɛf-, ˌɛnsɛfəˈlaɪtɪs, ˌɛnsɛfəˈlɪtɪk /

noun

1. inflammation of the brain

---

encephalitis Scientific  

/ ĕn-sĕf′ə-lī′tĭs /

1. Inflammation of the brain, usually caused by infection with a virus.

---

encephalitis Cultural  

1. An inflammation of the brain. Encephalitis may be caused by a virus or lead poisoning, or it may be a complication of another disease, such as influenza or measles. Encephalitis can cause permanent brain damage or death. It is also possible, however, to recover from it completely.

---

Other Word Forms

• encephalitic adjective
• postencephalitic adjective
• pseudoencephalitic adjective

Etymology

Origin of encephalitis

First recorded in 1835–45; encephal- + -itis

Example Sentences

There are allusions to the tragedies that befell him: the loss of a young daughter to measles encephalitis and his son’s near-fatal accident.

From The Wall Street Journal • Mar. 24, 2026

These infections were marked by encephalitis and frequently resulted in death, highlighting the increased pathogenic potential of this transmission route.

From Science Daily • Jan. 5, 2026

In rare cases chicken pox can cause a swelling of the brain, called encephalitis; an inflammation of the lungs, called pneumonitis; and stroke, which can result in hospitalisation and - very rarely - death.

From BBC • Aug. 28, 2025

Scores of studies show that the vaccine doesn’t cause encephalitis, that most potential side effects resolve quickly on their own, and serious adverse reactions are far rarer than measles complications.

From Salon • Aug. 26, 2025

In some areas of the United States the mosquito vector of western equine encephalitis has developed resistance.

From "Silent Spring" by Rachel Carson