Bovine coronavirus (BCoV) causes neonatal calf diarrhea, winter dysentery, and respiratory disease worldwide. However, its primary replication site remains uncertain, and systemic studies on tissue tropism are limited. We, therefore, intranasally inoculated colostrum-fed Holstein calves (6–13-day-old) with a BCoV isolate derived from diarrheic calf, and monitored clinical signs, gross and histopathological lesions, antigen distribution, and viral replication in multiple tissues. All calves were seropositive before challenge. Infected animals developed diarrhea without respiratory manifestations. Viral RNA appeared first in nasal swabs and subsequently in feces, yet viral load in nasal secretions was not associated with clinical signs. Apart from enlargement of the mesenteric lymph nodes, no characteristic gross lesions were observed. Digital RT-PCR and immunohistochemistry detected BCoV in tonsil, trachea, lung, liver, kidney, abomasum, and both small and large intestines, indicating epithelial tropism at each site. Although the inoculum originated from a diarrheic calf, histopathology revealed enteritis, mild interstitial pneumonia, tonsillitis, and hepatitis. These data indicate that BCoV initiates replication in respiratory epithelia and subsequently disseminates to the digestive tract, with no correlation between gross pathology and viral detection. We conclude that BCoV exhibits broad tissue tropism and may contribute to disorders beyond classical respiratory and enteric disease, thereby refining the current understanding of BCoV pathogenesis.
Streptococcus uberis, a major environmental pathogen, is frequently linked to recurrent or persistent intramammary infections, posing a challenge to mastitis control in dairy cattle. In this study, we characterized 112 S. uberis isolates recovered from bovine mastitis milk samples collected across South Korea between 2019 and 2024. Multilocus sequence typing revealed substantial genetic diversity, with all sequence types being newly assigned, and no evidence of a dominant clonal lineage. High levels of resistance to tetracycline (81.3%), erythromycin (75.9%), and pirlimycin (75.0%) were observed. Notably, 74.1% of the isolates were classified as multidrug-resistant. The corresponding resistance genes tetO (82.1%) and ermB (79.5%) were commonly detected and showed strong concordance with resistance phenotypes. Virulence-associated genes, including sua, mtuA, oppF, skc, and pauA, were widely detected (89.3-100%). All isolates were capable of biofilm formation, although the majority demonstrated weak biofilm-formation ability. This study provides important insights into the epidemiology and pathogenic potential of bovine mastitis-associated S. uberis isolates in South Korea and underscores the need for continued surveillance and prudent antimicrobial use to formulate effective mastitis-control strategies.IMPORTANCEStreptococcus uberis is a leading environmental cause of bovine mastitis worldwide, yet region-specific molecular epidemiological data remain limited in South Korea. To our knowledge, this study represents the first nationwide molecular characterization of mastitis-associated S. uberis isolates in South Korea, integrating MLST-based population analysis, antimicrobial susceptibility testing, resistance gene detection, and virulence profiling. The identification of exclusively novel sequence types indicates substantial genetic diversity within the regional population. The high prevalence of tetracycline and MLS-type resistance, closely associated with tetO and ermB, highlights the importance of continued monitoring of antimicrobial resistance in the dairy production. Additionally, the widespread detection of core virulence-associated genes and universal biofilm-forming capacity indicates conserved characteristics among mastitis-associated isolates. These findings provide baseline data to support future surveillance and control strategies targeting bovine mastitis-associated S. uberis.
The global spread of highly pathogenic avian influenza (HPAI) among poultry, wild birds, and mammals has increased the risk of infection in felines, including domestic and stray cats. Wild felids are particularly susceptible to H5N1 HPAI virus infection because they may consume the carcasses of infected birds. Fatalities associated with the consumption of raw pet foods prepared from poultry meat have been reported in both the United States and Korea. Given that high titers of avian influenza (AI) viruses have been detected in poultry meat, effective sterilization methods are essential to ensure the safety of raw pet food products. In this study, we evaluated the efficacy of electron beam (E-beam) irradiation—an established method for inactivating hazardous microorganisms in raw pet food—against duck meat experimentally contaminated with avian influenza (AI) virus. Shredded duck breast meat was inoculated with the low-pathogenic H5 subtype avian influenza virus A/Geese/Korea/H277/2022 (H5N3) and subjected to E-beam irradiation at doses ranging from 0 to 40 kGy. The D10 values calculated based on the nominal irradiation dose and the actual absorbed dose were 2.58 and 2.34, respectively. Based on the absorbed-dose D10 value, duck meat containing a high viral load (approximately 107.6 EID₅₀/g in the mock-irradiated control) was estimated to require approximately 17.63 kGy for complete viral inactivation.
BACKGROUND:A number of patients infected with severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) show a wide range of systemic complications. Previous studies have shown that acute SARS-CoV-2 infection can be accompanied by conjunctivitis, various forms of ocular inflammation and retinal vasculitis. However, long-term changes of the retina after SARS-CoV-2 infection have not been examined. In this study, we investigated neuroinflammation in the retina and optic nerve. METHODS:hACE2 Tg mice, serologically negative for SARS-CoV-2, were infected via intranasal installation with SARS-CoV-2. Protein expression was confirmed by immunofluorescence and western blotting. The activation of microglia and astrocytes was confirmed using quantitative real-time PCR. RESULTS:SARS-CoV-2 infection induced a decrease in inner retinal thickness and an increase in RGC death after 60 days. Activation of microglia and astrocytes was observed in the retina. Expression of the inflammatory cytokines Il-1β and TNF-α increased in the optic nerve, whereas microglial and astrocyte expression decreased. CONCLUSION:Our findings suggest that chronic neuroinflammation in the retina post SARS-CoV-2 infection contributes to retinal degeneration, potentially resulting in long-term visual disturbance.
Importance: Wild aquatic birds are reservoirs of avian influenza viruses (AIVs). South Korea has conducted national wild-bird surveillance since 2008 to enable early detection of highly pathogenic AIVs (HPAIVs) and rapid response in poultry. Objective: We investigated the distribution of AI viruses in fecal samples from wild bird habitats (and nearby poultry-farm areas) surveyed between September and March from 2019 to 2025 and identified associated epidemiological risk factors. Methods: Samples were screened for influenza A (M, H5, H7) genes using real-time reverse transcription polymerase chain reaction (PCR), subjected to virus isolation in embryonated chicken eggs, and subtyped by PCR and sequencing. Host species were identified through DNA barcoding. Relative risks (RRs) with 95% confidence intervals were estimated for province, month, and waterfowl density. Results: Overall prevalence of HPAI and low pathogenic AI (LPAI) virus was 0.10% and 3.21%, respectively. HPAI virus was continuously isolated since 2020-2021, except 2019-2020, while LPAI prevalence steadily increased (3.01%-4.35%). Twelve hemagglutinin (H1-H12) subtypes were identified in 1,722 isolates, and H3 (16.5%) was the most prevalent, followed by H5 (11.1%) and H7 (5.2%). LPAI H5N3 (55.7%) and H7N7 (75.5%) were the predominant H5 and H7 subtypes, respectively. Detection was higher in western coastal provinces, and higher mallard/spot-billed duck density and sampling in September-December were associated with increased risk. Conclusions and Relevance: Continued surveillance of migratory-bird habitats can provide early warning of HPAIV incursions and support targeted biosecurity measures in high-risk regions and seasons.
