Genomic epidemiology of two travel-associated pediatric measles viruses within the B3 Lineage.

BACKGROUND

Children's Hospital of Philadelphia (CHOP) identified a MeV case in late 2023 and also early 2025, both of which were associated with international travel. Of the 24 MeV genotypes, the B3 and D8 lineages have been the most prevalent globally since 2021. Initial genotyping indicated that the two CHOP isolates belong to the B3 lineage.

OBJECTIVES

To inform MeV molecular surveillance, we conducted a genomic epidemiology analysis to situate the CHOP strains within the global genetic landscape of past and present MeV B3 cases.

STUDY

DESIGN

We performed whole-genome amplification, genome assembly, and phylogenomics of our two MeV cases. These strains were then analyzed alongside all 168 National Center for Biotechnology Information near-full length MeV B3 genomes using population and evolutionary genetic approaches. This dataset includes strains isolated from 13 countries between 2005 and 2025.

RESULTS

The two CHOP strains form a monophyletic group with 39 other isolates from four countries; 36 clade members form a discrete network connected by a 15 single nucleotide polymorphism (SNP) cutoff. The CHOP clade shares a Q45H phosphoprotein mutation at a codon undergoing diversifying selection, as with a H593R hemagglutinin mutation carried by the 2025 CHOP strain. The CHOP clade likely diverged in 2019 and has a median root-to-tip distance of 0.020 compared to 0.017 for the other B3 strains, consistent with this clade encompassing the most recently divergent nodes.

CONCLUSIONS

Our work places the CHOP MeV cases within a diversifying and emergent global clade of the dominating B3 lineage that is a future risk due to ongoing B3 MeV transmission.