The current status of neonatal echovirus 11 infections in Japan: A comparison to the global situation

Enteroviruses (EVs) are one of the most common causes of severe neonatal infections. The spectrum of diseases varies with age, sex, and immune status. As molecular methods have evolved, several new EVs have been identified, bringing the total number of serotypes to over 100. Since 2022, the World Health Organization has published Disease Outbreak News on echovirus 11 (E11) infections due to an increase in severe neonatal E11 infections in several European countries. In Japan, several life-threatening neonatal cases were also reported in the summer of 2024. Clinical characteristics of severe cases include rapid clinical deterioration with multiorgan failure, hemophagocytic lymphohistiocytosis-like inflammatory features, and a high mortality rate. Male infants are likely to experience severe outcomes, specifically in neonates, onset soon after birth, and possible maternal peripartum infection. Meanwhile, older infants with aseptic meningitis often show mild, self-limited disease. Genomic characteristics indicate that a new recombinant genotype D5 is the predominant circulating E11 lineage worldwide. Recent severe neonatal cases linked to a closely related genetic variant that may have increased pathogenicity. This evidence suggests both viral evolution and immature neonatal immunity may contribute to the disease severity. Given the newly initiated nationwide surveillance in Japan, enhanced EV surveillance and rapid genomic characterization are crucial for early identification of severe E11 infection in neonates.