Proposal for the recognition of a new disease concept from Japan; Parechovirus A3-associated myalgia.

Parechovirus A3 (PeVA3) was first reported in 2004 and has been recognized as a causative agent of mild and severe infectious diseases among children. We first reported an outbreak of adult PeVA3-associated myalgia (PeVA3-M) in Yamagata, Japan in 2008. We have repeatedly observed PeVA3-M cases in 2011, 2014, and 2016, and identified the first child case in 2014. Reports of PeVA3-M have increased since 2014, indicating that recognition of PeVA3-M has spread across Japan. Findings showed that PeVA3-M commonly occurs among adults aged 30-40 years, particularly in males. Elevation of creatinine phospho kinase, C-reactive protein and myoglobin as well as magnetic resonance images suggest inflammation of muscles and/or fascia of four limbs. The patients recover within 1-2 weeks without any sequelae. A longitudinal molecular epidemiolog ical study in Yamagata revealed that PeVA3 strains cause a variety of diseases, ranging from mild to severe, including PeVA3-M, in subjects ranging from neonates to adults, irrespective of their genetic cluster. As PeVA3-M has not yet been reported abroad, more widespread recognition of PeVA3-M as an emerging disease is important. We hope this review will help clinicians and advance research related to PeVA3-M in Japan as well as around the world.