Viral Encephalitis

Abstract

Viral encephalitis can result from direct invasion of the brain or indirectly through immune‐mediated effects. Syndromes of infection‐associated encephalopathies can also occur without direct brain invasion, and autoimmune encephalitides can be triggered by viruses. Here, we review the epidemiology and pathogenesis of encephalitis by virus families, and consider diagnosis, management and prevention. Age, immune competency and geographic location influence aetiology. HSV is the commonest sporadic viral encephalitis in adults and older children in the developed world. Nonpolio enteroviruses and Japanese encephalitis virus are additional common causes in young children, particularly in developing countries. Rabies is the leading cause of fatal encephalitis worldwide. Outbreaks of infectious encephalitis may signal emergence of novel viruses or changes in distribution of known viruses. Better deployment and/or development of vaccines and therapies are required to prevent viral encephalitis. Further research is needed to clarify the role of immune modulation in viral encephalitis. Key Concepts Viral encephalitis (brain inflammation with cerebral dysfunction) can result from direct invasion of the brain or indirectly from immune‐mediated pathology. Viral‐associated encephalopathies such as those associated with influenza virus infection are not usually associated with detection of virus in the CSF. The causes of viral encephalitis are influenced by geographic location, age, immune competency, the availability of effective vaccines or antivirals and the season. Outbreaks of viral encephalitis can indicate emerging viral pathogens of public health significance or spread of vector‐borne and zoonotic viral encephalitides to new geographic locations. Increases of zoonotic encephalitis such as rabies have recently occurred in countries where they were previously eradicated, and indicate a global need for a one health (animal and human) approach to prevention. Empiric antiviral therapy should be commenced early in suspected viral encephalitis cases but promptly ceased when herpes simplex virus encephalitis has been excluded. There may be a role for early institution of immune suppression in some forms of viral encephalitis. Many cases of encephalitis are lost opportunities for prevention due to missed opportunities for vaccination or ineffective immunisation programs vaccines. Viral encephalitis continues to cause ongoing high burden of death and disability, particularly in childhood.