Atanas Vladimirov Demirev

Background: Influenza A(H3N2) has resurged in South Korea despite a shrinking pediatric population and high vaccination coverage. We examined correlates of host‐age state transitions on the H3N2 hemagglutinin (HA) genealogy. Methods: We analyzed 703 South Korean H3N2 HA sequences (2009–2025) in eight host‐age states (ages 0–4, 5–9, then 10‐year bands to 60 years and older). Discrete‐trait analysis and an epoch‐structured hierarchical generalized linear model (GLM) were fitted over 1700 HA trees, with epochs split at mid‐2020. Within‐year age‐label permutation provided the sampling control (one for the discrete‐trait analysis, 20 for the GLM). Results: Children aged 5–9 years showed the largest net source balance (+11.7 vs. +10.5 under permuted labels), reflecting a lower recipient‐side rate (0.39 vs. 1.08) rather than a higher source‐side rate (12.11 vs. 11.59). Of 56 routes, 18 were supported (Bayes factor ≥ 10) but only three exceeded the permutation control, two from this group. Observed labels fitted the genealogy 400 log‐likelihood units better, with 24% fewer transitions. Source‐group population size (posterior inclusion probability, 0.74) and vaccination coverage (0.66) were supported, both with negative coefficients; contact rate was not (0.016). Only population size exceeded the permutation null (0.74 vs. 0.65; p = 0.048). Conclusions: H3N2 HA lineage transitions in South Korea were age‐structured after accounting for sampling, most clearly for children aged 5–9 years. Their net source balance reflects a low recipient‐side rate rather than a high source‐side rate, and therefore describes lineage position rather than transmission intensity. These findings support age‐resolved genomic surveillance for interpreting such patterns.

Lee S, et al. J Vet Sci. 2026 ;27:e65. https://doi.org/10.4142/jvs.26088

Seoul (SEOV) and Hantaan (HTNV) orthohantaviruses are significant zoonotic pathogens responsible for hemorrhagic fever with renal syndrome. Here, we investigated the molecular evolution of SEOV and HTNV through phylogenetic and bioinformatic analyses using complete genome sequences of their large (L), medium (M), and small (S) gene segments. Despite similar epizootic cycles and clinical symptoms, SEOV and HTNV exhibited distinct genetic and evolutionary dynamics. The phylogenetic trees of each segment consistently showed major genetic clades associated with the geographical distribution of both viruses. Remarkably, SEOV M and S segments exhibit higher evolutionary rates, rapidly increasing genetic diversity, and a more recent origin in contrast to HTNV. Reassortment events were infrequent, but both viruses appear to utilize the M gene segment in genetic exchanges. SEOV favors the L or M segment reassortment, while HTNV prefers the M or S segment exchange. Purifying selection dominates in all three gene segments of both viruses, yet SEOV experiences an elevated positive selection in its glycoprotein Gc ectodomain. Key amino acid differences, including a positive ‘lysine fence’ (through residues K77, K82, K231, K307, and K310) located at the tip of the Gn, alongside the physical stability around an RGD-like motif through M108-F334 interaction, may contribute to the unique antigenic properties of SEOV. With the increasing global dispersion and potential implications of SEOV for the global public health landscape, this study highlights the unique evolutionary dynamics and antigenic properties of SEOV and HTNV in informing vaccine design and public health preparedness.