PHWR Public Health Weekly Report

Objectives: This study aims to identify the characteristics of domestic malaria by examining the status of malaria diagnoses referred to the Korea Disease Control and Prevention Agency (KDCA) between 2021 and 2025.
Methods: Malaria diagnostic samples referred to the KDCA were classified into private sector submissions from medical institutions and public sector submissions from public health centers and military hospitals. Malaria infection was confirmed by microscopic examination or molecular detection. Patient characteristics, such as parasitemia levels, were estimated using a formula based on real-time polymerase chain reaction (PCR) cycle threshold (C_t) values.
Results: The KDCA collected a total of 2,508 malaria-positive samples between 2021 and 2025. Domestic Plasmodium vivax accounted for 96.2% of malaria cases, whereas imported malaria cases were caused by Plasmodium falciparum (75.8%), Plasmodium ovale (16.8%), P. vivax (5.3%), and P. falciparum–P. ovale coinfection (2.1%). The proportion of diagnostic referrals from public health centers was peaked at 58.9% in 2023 and subsequently decreased, whereas the proportion from secondary hospitals gradually increased, reaching 43.8% in 2025. In contrast, the proportion from military hospitals markedly declined from 26.8% in 2024 to 9.9% in 2025. Based on parasitemia estimates calculated from real-time PCR C_t values, most patients in 2024–2025 showed parasitemia levels of 8,000/μl or higher.
Conclusions: Accurate malaria diagnosis is essential for effective disease prevention and control. This study is expected to facilitate patient management and contribute to national malaria elimination by providing basic information through an analysis of the status of malaria diagnosis over five years.

Objectives: This study aims to detect unreported vector-borne pathogens with the potential for introduction into the Republic of Korea (ROK) owing to climate change and increasing international travel and to evaluate the need for proactive surveillance strategies that address gaps in existing surveillance systems.
Methods: A retrospective analysis was conducted using 5,674 clinical samples collected between 2023 and 2025 from patients with suspected vector-borne infections who tested negative for nationally notifiable vector-borne diseases. Ten candidate pathogens were selected based on their occurrence in neighboring countries and their potential for transmission by vectors present in the ROK. A stepwise analytical workflow was applied, encompassing quantitative reverse transcription polymerase chain reaction (qRT-PCR)-based screening, followed by Sanger sequencing and phylogenetic analysis.
Results: Among the 5,674 samples, two cases of tick-borne Oz virus infection were identified, while the remaining nine target pathogens were not detected. One case was classified as an imported infection based on documented travel to Japan and a confirmed history of tick exposure. The second case occurred in a patient without international travel history, suggesting the potential presence of Oz virus within the domestic environment.
Conclusions: This study identified evidence of potential importation and possible domestic transmission of previously unrecognized pathogens that had not been detected through existing surveillance system. The findings highlight the need to strengthen vector and wildlife surveillance, expand molecular diagnostic capacity, and establish an integrated One Health surveillance framework to improve early detection and response to emerging infectious diseases not currently included in routine surveillance programs.

Objectives: Andes virus (ANDV) is an exceptional hantavirus for which human-to-human transmission has been repeatedly reported, and it causes hantavirus cardiopulmonary syndrome with high lethality in South America. This review aims to summarize the epidemiological and clinical features of hantavirus infections and their transmission routes, and to examine transmission patterns within a confined, high-density environment and future public health response strategies, using the 2026 ANDV outbreak on the MV Hondius cruise ship as a case study.
Methods: Drawing on publicly available reports from the World Health Organization (WHO), the European Centre for Disease Prevention and Control, the Pan American Health Organization, and the Korea Disease Control and Prevention Agency, as well as relevant literature, we reviewed the characteristics of hantavirus infections and this outbreak.
Results: The MV Hondius departed from Ushuaia, Argentina, on April 1, 2026. On May 2, the UK International Health Regulations (IHR) National Focal Point formally alerted the WHO to a cluster of severe acute respiratory illnesses. By May 27, 13 individuals (11 confirmed and 2 probable cases) had been infected, and 3 had died. Genomic analysis revealed no more than one single-nucleotide polymorphism difference among patients, indicating onboard human-to-human transmission following a single or a very small number of zoonotic spillover events; the effective reproduction number was estimated to be 0.7 on May 22. Major factors contributing to transmission included advanced age (mean, approximately 65 years), shared cabins, communal indoor spaces, and close caregiving or clinical contact.
Conclusions: This outbreak demonstrates that pathogens with limited human-to-human transmissibility can nevertheless be amplified in a closed, high-density environment. Prompt identification, international coordination under the IHR, and efficient risk communication were central to controlling the outbreak, and preparedness for potential importation requires routine assessment of travel history, surveillance for suspected cases, and access to rapid diagnostic testing.