Genetic comparison of human parainfluenza virus type 3 detected in respiratory samples from patients with encephalopathy and airway inflammation in Aichi Prefecture, Japan.

Human parainfluenza virus type 3 (HPIV-3, Human respirovirus 3) is the second most frequently detected virus after human respiratory syncytial virus (HRSV) in lower respiratory tract infections in children. HPIV-3, like its close relative respiratory viruses, HRSV and influenza virus, may cause encephalopathy, but the relevance of HPIV-3 as a pathogenic factor in encephalopathy is unknown. We attempted to detect HPIV-1 through 4, HRSV, and human metapneumovirus (HMPV) in 136 patients with encephalitis/encephalopathy, or suspected encephalitis/encephalopathy during a 6-year period from 2014 to 2019. As a result, HPIV-3 was detected most frequently in 6 patients, followed by HRSV in 3. The HPIV-3 strains detected were closely related to those detected in a patient with respiratory disease at the same period. Although HPIV-3 is less recognized than HRSV as a triggering virus of encephalopathy, our results suggest that HPIV-3 is at least as important as HRSV. Surveillance of the causative virus of encephalopathy, including HPIV-3, would help to clarify the actual status of encephalopathy, the cause of which is currently reported in less than half of cases in Japan.