Chanhee Chae

Background: Evaluation of the reproductive efficacy of a modified-live vaccine (MLV) based on porcine reproductive and respiratory syndrome virus-2 (PRRSV-2). Objective: The objective of this study was to evaluate the efficacy of a MLV based on porcine PRRSV-2 against a heterologous Korean PRRSV-2 lineage 1 strain challenge in pregnant sows. Animals: Twelve pregnant sows from PRRSV-free farms were randomly assigned to three groups (four sows per group). Methods: Sows in the vaccinated-challenged group received a 2.0 mL intramuscular dose of PRRSV-2 MLV and were subsequently challenged intranasally with a heterologous PRRSV-2 strain. Results: Vaccinated-challenged sows improved reproductive performance, including a higher number of live-born piglets and fewer stillbirths compared with unvaccinated-challenged sows. Viral genomic loads were lower in vaccinated-challenged sows and their offspring as well. Vaccinated-challenged sows also elicited a significantly higher frequency of PRRSV-2 specific interferon- γ secreting cells. Discussion: These findings demonstrated that the PRRSV-2 MLV administered to pregnant sows provide protection against heterologous challenge through clinical, virological, and immunological evaluation.

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause substantial economic losses worldwide, and certain lineages circulate in specific countries. Lineage Korean A (LKA), B (LKB), and C (LKC) have been reported exclusively in Korea. However, studies on LKA and LKB have been limited to strains isolated before 2015. In this study, we analyzed the genetic and pathogenic characteristics of SNUVP2403A and SNUVP2407B strains isolated in 2024. Based on ORF5 phylogenetic analysis, SNUVP2403A and SNUVP2407B were classified as LKA and LKB, respectively. No recombination was detected in SNUVP2403A, whereas SNUVP2407B was identified as a recombinant between NADC30 and JB15‐N‐PJ10‐GN. In the animal infection study, the pigs inoculated with SNUVP2403A had a mortality rate of 8.3% (1/12 pigs), and clinical signs such as nasal discharge, coughing, eyelid edema, and cyanosis were observed. The group inoculated with SNUVP2407B exhibited only mild respiratory symptoms, and all pigs survived throughout the experiment. Therefore, it was demonstrated that SNUVP2403A is more virulent than SNUVP2407B. In addition, SNUVP2407B exhibited significantly lower pathogenicity than previously reported LKB strains. In conclusion, this study provides a systematic characterization of SNUVP2403A and SNUVP2407B and improves our understanding of the genetic diversity and pathogenicity of PRRSV circulating in Korea.

Background: A field efficacy trial was conducted on three farms to evaluate a novel combined vaccine containing porcine circovirus types 2a/d (PCV2a/d), Mycoplasma hyopneumoniae , and M. hyorhinis . Methods: Three farms with a history of subclinical PCV2 infection, enzootic pneumonia, and polyserositis were enrolled. Each farm included 40 piglets (18 days old), which were randomly allocated to vaccinated or unvaccinated groups. Pigs in the vaccinated group received a single 2‐mL intramuscular dose of the combined vaccine at 21 days of age, while unvaccinated pigs received phosphate‐buffered saline. Results: Vaccination significantly improved ( p < 0.05) body weight and average daily weight gain on all three farms compared with unvaccinated pigs. Vaccinated pigs mounted protective humoral and cellular immune responses against PCV2, M. hyopneumoniae , and M. hyorhinis . Furthermore, vaccination reduced viral and mycoplasmal loads in serum, laryngeal, and nasal samples and decreased the severity of associated lesions. Conclusions: The combined vaccine demonstrated strong efficacy under field conditions, providing protection against subclinical PCV2 infection, enzootic pneumonia caused by M. hyopneumoniae , and polyserositis caused by M. hyorhinis . These findings support its potential as an effective intervention for improving both health and productivity in swine herds.

Background: The efficacy of a novel combined vaccine targeting porcine circovirus types 2a/d (PCV2a/d), Mycoplasma hyopneumoniae, and M. hyorhinis was evaluated in a controlled challenge study. Methods: A total of 45 pigs were randomly allocated into nine groups (five pigs per group). Vaccinated groups received a single 2 mL intramuscular dose of the combined vaccine and were subsequently challenged with PCV2a, PCV2d, M. hyopneumoniae, and M. hyorhinis. Unvaccinated groups received a single 2 mL intramuscular dose of phosphate-buffered saline (0.01 M, pH 7.4). Growth performance, systemic adaptive immune (humoral and cellular) responses, viremia, laryngeal and nasal mycoplasma loads, and histopathological lesions were assessed. Results: Vaccinated pigs exhibited enhanced growth performance and elicited systemic immune responses, including both humoral and cellular immunity, against all four pathogens. Vaccination also significantly reduced viremia, mycoplasmal loads in laryngeal and nasal swabs, and the severity of associated lesions compared with unvaccinated controls. Conclusions: These results indicated that the combined vaccine was efficacious and conferred protection against PCV2a, PCV2d, M. hyopneumoniae, and M. hyorhinis challenge under experimental conditions. This combined vaccine represented an effective strategy to enhance growth performance and control complex co-infection in swine populations.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major challenge to swine health and production globally. Among PRRSV-2 lineages circulating in South Korea, the lineage 1J (L1J)—recently reclassified from lineage Korean clade C (LKC)—has emerged as an epidemiologically significant variant, accounting for approximately 15%–28.9% of cases in recent years. Despite its widespread circulation, data on the reproductive pathogenicity of L1J strains remain scarce. To address this gap, an experimental infection study was conducted to evaluate the reproductive pathogenicity of PRRSV strain SNUVR220803 in pregnant gilts. This strain, originally classified within L1J and is characterized by multiple recombination events with lineage 5 viruses-presumably the Ingelvac PRRS MLV vaccine strain, as well as a unique four-amino acid deletion in Nsp2. Eight PRRSV-naïve pregnant gilts at 86 days of gestation were randomly assigned to either the infected (n = 4) or control (n = 4) group. Inoculated gilts exhibited elevated rectal temperatures at 2 days postinoculation (dpi), followed by clinical signs including anorexia and lethargy between 7 and 10 dpi. Clinical recovery was observed by 14 dpi; however, all infected gilts subsequently experienced abortion or premature farrowing at gestational days 109–112, during which no viable piglets were recovered, except for two that died within 30 min after birth without trauma, indicating intrauterine death or severe neonatal compromise. These findings demonstrate that SNUVR220803 possesses markedly higher reproductive pathogenicity than previously reported L1J strains, such as K07-2273. Given that PRRSV reproductive virulence cannot be fully explained by ORF5-based classification alone, the heightened pathogenicity of SNUVR220803 is likely attributed to a combination of mutations in nonstructural and structural proteins. These results highlight the need for continued molecular surveillance and pathogenicity studies of emerging PRRSV strains.

Background/Objectives: Porcine circovirus type 2d (PCV2d) is the predominant genotype associated with porcine circovirus-associated disease (PCVAD), leading to significant economic losses. In South Korea, current vaccine lot-release testing relies on a T/C-ratio-based guinea pig assay, which lacks scientific justification and methodological robustness. This study aimed to develop and validate a statistically defined in-house ELISA using rabbit-derived polyclonal antibodies against PCV2d for the standardized evaluation of immunogenicity. Methods: Polyclonal IgG was generated by immunizing a rabbit with inactivated PCV2d, and it was purified through Protein A chromatography. Guinea pigs (n = 18) were immunized with IMMUNIS^® DMVac, an inactivated PCV2d vaccine candidate developed by WOOGENE B&G, at different doses. In-house ELISA parameters were optimized (antigen coating, blocking agent, and substrate incubation), and analytical performance was evaluated by ROC, linearity, reproducibility, and specificity. Sera from guinea pigs and pigs were analyzed under validated conditions. Results: The optimal performance was achieved using 10⁵ genomic copies/mL of the antigen coating and a 5% BSA blocking agent. The assay showed strong diagnostic accuracy (AUC = 0.97), reproducibility (CVs < 5%), and linearity (R² = 0.9890). Specificity tests with PCV2a, PCV2b, and PRRSV showed minimal cross-reactivity (2 = 0.1815) and acceptable agreement (bias = −0.21) between guinea pig and porcine sera. The validated cut-off (S/P = 0.4) enabled accurate classification across both species and aligned well with commercial kits. Conclusions: The in-house ELISA offers a robust, reproducible, and scientifically validated platform for immunogenicity verification, supporting its application in Korea’s national lot-release system. Homologous competition assays with PCV2d are planned to further confirm antigen specificity.