Acute viral encephalitis: the recent progress

Area of Science:

• Neurology
• Infectious Diseases
• Public Health

Background:

• The Japanese control law for infectious diseases categorizes acute viral encephalitis, with most cases falling under Category IV, requiring reporting from sentinel hospitals.
• Herpes simplex virus type 1 (HSV-1) encephalitis is the most common form of viral encephalitis.
• Advancements in diagnostic techniques like polymerase chain reaction (PCR) have improved the identification of various central nervous system (CNS) infections caused by HSV-1 and HSV-2.

Purpose of the Study:

• To review trends in Herpes Simplex Virus (HSV) central nervous system (CNS) infections in the Kyushu and Okinawa regions of Japan since 1990.
• To identify changes in the prevalence of different types of viral encephalitis and other CNS infections.
• To highlight emerging and reemerging infectious disease threats affecting the CNS in Japan.

Main Methods:

• A retrospective survey of HSV CNS infections was conducted in the Kyushu and Okinawa regions from 1990 onwards.
• Data analysis focused on identifying trends in the incidence and types of viral encephalitis and related CNS infections.
• Review of existing literature and surveillance data on infectious CNS diseases in Japan.

Main Results:

• A notable increase in a new subtype of non-herpetic acute limbic encephalitis was observed.
• The incidence of Japanese encephalitis (JE) has significantly decreased in Japan, with only a few cases reported annually.
• Imported emerging and reemerging CNS infections, such as Murray Valley and West Nile encephalitis, pose potential risks.

Conclusions:

• While JE incidence has declined, it remains a concern for immunocompromised individuals.
• Influenza-associated encephalitis/encephalopathy presents a significant threat to both children and adults.
• Continuous surveillance and awareness of diverse viral CNS infections, including HSV and emerging pathogens, are crucial for public health in Japan.