Encephalitis.

Brain inflammation secondary to encephalitis is an urgent global emergency and presents multiple opportunities to reduce current substantial morbidity and mortality. Aetiologies can be divided into infectious and autoimmune causes. In this Seminar, we highlight pragmatic clinical approaches to recognise and distinguish the most common pathogenic viruses and emerging range of autoantibodies encountered in routine practice. These pre-test impressions are judiciously shaped by valuable, simple investigations-particularly serum and cerebrospinal fluid nucleic acid and autoantibody testing-to identify the precise causative agent. This clinically led approach ensures early recognition of encephalitis subtypes, facilitates the timely administration of antivirals and immunotherapies proven to improve patient outcomes, and minimises the frequent misdiagnosis of autoimmune encephalitis. Finally, we review emerging targeted therapeutic approaches, measurements of clinical encephalitis outcomes, and environmental and vaccine-centred strategies to improve prevention, diagnosis, and care for patients with encephalitis, cognisant of long-term patient, caregiver, and economic burdens.