Comparative Analyses of the Epidemiology and Clinical Findings of Herpes Simplex Virus and Varicella-Zoster Virus Encephalitis In 2012-2021

We conducted comparative analyses of (i) the epidemiology of herpes simplex encephalitis (HSE) and herpes zoster encephalitis (HZE) in elderly patients at our hospital in Kurume, Japan in 2012–2021 and (ii) the patients’ clinical findings. Compared to the 2002–2011 values, the 2012–2021 incidence of HSE decreased from 14 to nine cases and that of HZE increased from four to eight cases; the HZE patients’ average age was 79.6 years, indicating the population’s aging (p=0.02). The comparison of clinical findings revealed that all of the HSE patients experienced acute limbic encephalitis, whereas only half of the HZE patients did (p=0.03). There was no significant between-group difference in the cerebrospinal fluid PCR positivity rate. MRI findings demonstrated between-group differences: unilateral predominance in HSE and bilateral prevalence in HZE. The main invasion routes from reactivation in HSE were via the olfactory nerve, brainstem, and meninges. HZE also showed hematogenous spread, with one case each of disseminated rash and chickenpox. Antibody titer tests of several patients at the onset of both types of encephalitis showed enzyme-immunoassay IgG-positive values for both viruses, which suggests that both viruses were repeatedly reactivated in the brain ganglia and parenchyma and other organs.