CROI 2025 Abstract eBook

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Poster Abstracts

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300

Understanding the Evolutionary Framework and Transmission Dynamics of Mpox in South Korea Minji Lee, Chihwan Choi, Sang Eun Lee, Gyuri Sim, Jin-Won Kim, Myung-Min Choi, Hwajung Yi, Yoon-Seok Chung Korea Disease Control and Prevention Agency, Cheongju-si, South Korea Background: The 2022 global mpox outbreak is characterized by the accumulation of APOBEC3(A3)-mediated mutations through human-to human transmission, closely linked to behavioral epidemiological traits. This accumulation may have contributed to fluctuations in transmission dynamics. The virus underwent accelerated evolution through rapid transmission networks, with clustered transmission from sexual networks involving anonymous partners facilitating the buildup of A3-dependent variants and contributing to genetic drift. Methods: Clinical samples were collected from 139 mpox patients in South Korea between 2022 and 2024 to investigate these aspects. Libraries for whole genome sequencing were prepared using probe-capture hybridization. The resulting high quality sequences were utilized for phylogenetic and mutation analyses. Results: In 2022, South Korea reported four imported mpox cases, including one involving a healthcare worker, all linked to sub-lineages B.1.1 and A.2.1. By 2023, cases surged to approximately 150, primarily associated with a group having significant epidemiological ties to Japan. The index case 2023 belonged to clade IIb sub-lineage C.1 and exhibited the unique L16F mutation, also found in genomes from Japan, Taiwan, and Belgium but absent in those from Germany, the USA, and Canada. South Korea then experienced sustained local transmission for about six months, with all patients showing the L16F mutation. Over 80% of cases involved close contact with anonymous partners, frequently through social media or visits to saunas, complicating contact tracing and leading to increased informal encounters and superspreading. Nearly all cases from 2023 to 2024 were dominated by a single virus lineage. To further understand transmission dynamics, we identified eight sub-clusters based on shared mutations, primarily linked to the activity of A3 deaminases with antiviral functions. The mutation hotspots are associated with structural integrity, such as ankyrin repeat/F-box proteins, while A3-dependent mutations act as barriers to cell-free transmission, promoting contact-dependent transmission. This shift enhances the virus's ability to establish localized infections, complicating containment efforts and driving molecular evolution characterized by low adaptation costs under natural selection pressure. Conclusions: Continuous monitoring and analyzing these dynamics are essential for effective public health policy formulation and a suitable global response to mpox cases. Fine-Tuning Viral Adaptation Through Genome Retraction: Insights From Mpox Outbreaks in South Korea Yoon-Seok Chung, Minji Lee, Chihwan Choi, Sang Eun Lee, Gyuri Sim, Jin-Won Kim, Hwachul Shin, Hwajung Yi Korea Disease Control and Prevention Agency, Cheongju-si, South Korea Background: Since 2022, the global population has experienced an unusual outbreak of mpox, characterized by the distinctive epidemiology of heavy-tailed sexual network partnerships within specific populations. These epidemiological characteristics resulted in an initial rapid outbreak driven by exclusive human to-human transmission within specific populations, which facilitated a broader range of viral evolution than initially anticipated. Methods: Genomic surveillance of mpox-positive cases in South Korea (2022–2024) employed hybrid whole-genome sequencing with long- and short-read methods. The high-quality genomes were used for phylogenetic and molecular evolution analyses. Results: The key characteristic of the mpox outbreak in South Korea was transmission heterogeneity. The spread of the disease was significantly influenced by specific communities and environmental contexts, with particular populations playing a pivotal role in the transmission dynamics. In response to these localized transmission patterns, the virus underwent molecular

evolution due to selective pressures from sustained outbreaks throughout 2023 and 2024. As transmission remained uneven, the virus accumulated genetic variations, including both mutations and genome retractions, which enhanced its adaptation to the host and optimized transmissibility. This study's genomic surveillance identified five cases of genomic deletions in key functional regions, including growth factors, apoptosis inhibitors, IL-18 binding proteins, BCL-2-like proteins, and NF-kB regulatory factors. These findings support the hypothesis that such deletions enable the virus to modulate host cell physiological processes, fine-tuning immune responses and cell survival to create optimal conditions for prolonged replication. Specifically, by adjusting the host transcriptome, the virus may induce a balanced immune response while regulating cell survival, thus promoting long-term infection. This transcriptome modulation could act as an evolutionary mechanism, facilitating the virus's transition to a chronic infection state. Conclusions: Importantly, the genetic deletions identified in this study do not fully suppress the host’s immune response but rather maintain a moderate state, allowing for co-evolution between the virus and the host. Such a transition to chronic infection could have profound implications for the transmission dynamics and epidemiology of infectious diseases. Discovery of Aberrant Genomic Rearrangement in an Mpox Virus Genome Observed in a Japanese Patient Hidetoshi Igari, Eiji Ido, Toshibumi Taniguchi, Takayuki Ishige Chiba University, Chiba, Japan Background: The surge of Mpox outbreak (clade IIb) which initially started in Europe/America in May 2022 eventually reached Asia a little later, and the first patient in Japan was identified in July 2022. A total of 249 cases have been reported to date in the country. Three patients visited our hospital. As noteworthy news, clade I appears to be jumping out of Africa. Appearance of a new variant (clade Ib) can be part of the reasons of this rapid expansion of viral habitats. Thus, genetic analyses of Mpox should be conducted in light of viral evolution. Methods: Three patients were all male and had typical lesions such as pustules and scabs on their body surfaces. The specimens (termed Mpox1-3 respectively) were collected from pustules and scabs on the first day of examination in 2023. DNAs were extracted and subjected to WGS using iSeq100 after long-range PCR. Virus isolation was attempted using VERO cells. Results: The WGS has revealed that all of three Mpox viruses belonged to clade IIb, lineage B.1.3. Mpox2 had only several additional mutations compared to Mpox1. Surprisingly, Mpox3 was found to have a very long deletion (nearly 6kbp-long) spanning the genomic positions 6,500 to 11,000. In addition, a much longer genomic portion (30kbp-long, the positions 160,000 to 190,000 just in front of 3’-ITR) was invertedly inserted at the deleted position. It means that this inverted genomic fragment is existing as duplicated, although the direction is opposite. The copy number of this aberrant rearrangement was confirmed by digital PCR. The viruses were isolated from all 3 specimens. The growth-kinetics indicated that the Mpox3 maintained its robust replicative property showing with slightly fusogenic CPEs. Conclusions: The WGS has revealed that all of three Mpox viruses belonged to clade IIb, lineage B.1.3. Mpox2 had only several additional mutations compared to Mpox1. Surprisingly, Mpox3 was found to have a very long deletion (nearly 6kbp-long) spanning the genomic positions 6,500 to 11,000. In addition, a much longer genomic portion (30kbp-long, the positions 160,000 to 190,000 just in front of 3’-ITR) was invertedly inserted at the deleted position. It means that this inverted genomic fragment is existing as duplicated, although the direction is opposite. The copy number of this aberrant rearrangement was confirmed by digital PCR. The viruses were isolated from all 3 specimens. The growth-kinetics indicated that the Mpox3 maintained its robust replicative property showing with slightly fusogenic CPEs.

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Poster Abstracts

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CROI 2025