Nationwide patterns of PRRSV detection, seasonality, and PRRSV-PCV2 co-detection in pigs with respiratory symptoms in the Republic of Korea, 2022-2024

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major viral pathogen associated with respiratory symptoms in swine production systems. This study investigated nationwide patterns of PRRSV detection, seasonal variation, and co-detection with porcine circovirus type 2 (PCV2) using lung samples obtained from pigs with respiratory symptoms in the Republic of Korea from 2022 to and 2024. A total of 2,476 samples were analyzed using real-time reverse transcription–polymerase chain reaction, and 62.4% were found to be positive for PRRSV. The annual positivity rate increased from 59.7% in 2022 and 59.8% in 2023 to 67.8% in 2024. Among all samples, 38.0% were positive for PCV2, with positivity rates increasing from 28.4% in 2022 to 48.7% in 2024. PRRSV-2 was consistently the predominant genotype, whereas PRRSV-1 and co-detection infections were detected at lower frequencies. Marked seasonal variation was observed, with higher detection rates in autumn and winter than in summer. In addition, PRRSV positivity was significantly higher in PCV2-positive samples than in PCV2-negative samples, indicating frequent co-detection under field conditions. Multivariate logistic regression analysis identified season, PCV2 detection, and year as significant factors associated with PRRSV detection. These findings demonstrate that PRRSV remains widely prevalent in Korean swine farms, with clear seasonal patterns and frequent co-detection with PCV2, highlighting the importance of integrated respiratory symptoms management strategies.