Proposal for the Recognition of a New Disease Concept from Japan: Parechovirus A3-Associated Myalgia

Severe Generalized Epidemic Myalgia in an Adult due to Human Parechovirus Type 3: A Case Report

Parechovirus A type 3 (PeVA3) is most commonly transmitted to adults from children. Although PeVA3 infection is rarely diagnosed, as the symptoms are generally mild and self-limiting, this infection has been associated with epidemic myalgia in Japan. The patient, a 37-year-old man, presented with severe generalized myalgia, inability to open his mouth, and orchitis, which resolved over a period of 10 days. All members of his family were thought to have been infected with PeVA3 during a visit to an amusement park. Although the source of infection and inability to open his mouth are atypical, the acute generalized muscle symptoms made us suspect epidemic myalgia and enabled us to make a diagnosis of PeVA3 infection.

Recombinant parechovirus A3 possibly causes various clinical manifestations, including myalgia; findings in Yamagata, Japan in 2019

BACKGROUND

Parechovirus A3 was first reported in 2004 and has been recognized as a causative agent of mild and severe infections in children. Since we first reported an outbreak of adult parechovirus A3-associated myalgia in Yamagata, Japan in 2008, this disease has since been recognized across Japan, but has not yet been reported from other countries.

AIM

We analysed 19 cases of parechovirus A3 infections identified in Yamagata in 2019 to further clarify the epidemiology of this disease.

METHODS

We performed phylogenetic analyses of parechovirus A3 isolates and analysed the clinical manifestations and the genomic clusters.

RESULTS

There were two clusters, with cluster 2019B replacing 2019 A around October/November. Phylogenetic analysis revealed that 2019B cluster strains and Australian recombinant strains, which appeared between 2012 and 2013, were grouped in one cluster at non-structural protein regions, suggesting that the ancestor to these regions of 2019B cluster strains were Australian recombinant lineage strains. The strains from both clusters caused various infections in children including myalgia. These findings strongly support that parechovirus A3 strains cause myalgia and other paediatric infections irrespective of the virus strains involved, including recombinant strains.　　.

CONCLUSIONS

We have reported repeatedly sporadic cases of myalgia and here showed that recombinant strains also cause myalgia. We hope our experiences will help better understand these infections and possibly result in detection of more cases in the world.

Characterization of Pathogenesis and Inflammatory Responses to Experimental Parechovirus Encephalitis

Human parechovirus type 3 (PeV-A3) infection has been recognized as an emerging etiologic factor causing severe nerve disease or sepsis in infants and young children. But the neuropathogenic mechanisms of PeV-A3 remain unknown. To understand the pathogenesis of PeV-A3 infection in the neuronal system, PeV-A3-mediated cytopathic effects were analyzed in human glioblastoma cells and neuroblastoma cells. PeV-A3 induced interferons and inflammatory cytokine expression in these neuronal cells. The pronounced cytopathic effects accompanied with activation of death signaling pathways of apoptosis, autophagy, and pyroptosis were detected. A new experimental disease model of parechovirus encephalitis was established. In the disease model, intracranial inoculation with PeV-A3 in C57BL/6 neonatal mice showed body weight loss, hindlimb paralysis, and approximately 20% mortality. PeV-A3 infection in the hippocampus and cortex regions of the neonatal mouse brain was revealed. Mechanistic assay supported the in vitro results, indicating detection of PeV-A3 replication, inflammatory cytokine expression, and death signaling transduction in mouse brain tissues. These in vitro and in vivo studies revealed that the activation of death signaling and inflammation responses is involved in PeV-A3-mediated neurological disorders. The present results might account for some of the PeV-A3-associated clinical manifestations.