Which of the following statements about encephalitis is true?

A. Encephalitis is most often caused by viral infections, not exclusively bacterial. B. Encephalitis is inflammation of the brain tissue, typically due to infection or autoimmune processes. C. Muscle pain may occur but is not the primary symptom; neurological symptoms like headache, fever, confusion, and seizures are more common. D. Encephalitis can be severe and life-threatening, requiring prompt medical treatment.