Emergence of Human Parechovirus Type 5 Meningitis in Japan, 2025.

Human parechovirus type 5 (HPeV-5) is rarely reported, and, thus, its clinical and virological features remain unclear. This study describes the first cluster of HPeV-5 meningitis in Japan and characterizes its clinical, laboratory, and molecular features. Six infants aged 13-42 days were identified at three municipal hospitals in Kobe, Japan, during a six-week period in summer 2025. Symptoms included fever (6/6), mottled skin (4/6), poor feeding (3/6), and rash (2/6). None developed thrombocytopenia, liver dysfunction, or cerebrospinal fluid (CSF) pleocytosis; one had leukopenia. Two infants who were tested had hyperferritinemia that persisted after defervescence. Fever resolved within three days in all infants, and all were discharged without sequelae. A polymerase chain reaction detected HPeV-5 in the CSF of all infants. A phylogenetic analysis demonstrated high VP1 nucleotide identity (>97%) with strains in Sapporo, Japan (2018), Australia (2019), and USA (2024), suggesting the circulation of a nearly identical lineage across multiple regions. HPeV-5 was also detected in 14 additional non-meningitis cases during the same period, indicating concurrent circulation in the community. These results indicate that HPeV-5 causes meningitis in young infants, even without CSF pleocytosis, and was associated with favorable outcomes in this case series. Continued molecular epidemiological surveillance is warranted.