Current epidemiology of infectious encephalitis: a narrative review.

Background: Infectious encephalitis poses a global health challenge with a high mortality and severe neurological consequences in survivors. Emerging pathogens and outbreaks are reshaping the patterns of the disease.

Objective: To understand the current epidemiology for improving prevention, diagnosis, and treatment.

Sources: MEDLINE/PubMed was searched using "encephalitis" and related MeSH terms from 2020 to September 2024. Population-based and case-control studies on encephalitis were searched for without time restrictions. Other studies known by the authors were also included.

Content: The incidence of infectious encephalitis ranged from 1.4 to 13.8 cases per 100,000 per year with a bimodal peak in infants and older adults. Herpes viruses remain the most common causes of sporadic encephalitis with Herpes simplex virus type 1 and Varicella Zoster virus reported most frequently. In endemic regions, arboviruses such as Japanese encephalitis virus and West Nile virus contribute significantly to the disease burden. Climate change is adding to the spread of these vector-borne viruses and thereby both altering the geographic distribution of causative agents and increasing the frequency of outbreaks. Evidence on risk factors associated to encephalitis is scarce and hampered by the absence of population-based case-control studies. The prognosis of infectious encephalitis remains unchanged during recent decades with high case-fatality rates and may vary according to e.g. aetiology, age, and presence of immuno-compromising conditions or other comorbidities. Importantly, a substantial proportion of survivors are left with disabling neurological sequalae.

Implications: The findings underscore the importance of public health surveillance and prevention strategies to address the changing epidemiology of encephalitis. This can be pursued through vaccination programs and vector control efforts. Future research should focus on identifying risk factors, improving diagnostic tools, optimizing current treatment as well as exploring novel therapies for patients with encephalitis. Timely treatment and specialised post-hospital rehabilitation remain essential for patient management.