Unraveling the Complex Dynamics of Porcine Respiratory Disease Complex (PRDC) Pathogens in the Spanish Swine Production

The porcine respiratory disease complex (PRDC) poses a significant economic burden on global swine production and adversely impacts animal health and welfare due to its multifactorial nature and complex pathogen interactions. Here, through a comprehensive epidemiological analysis of 6,017 clinical cases from Spanish swine farms collected between January 2020 and May 2024, we evaluated the frequency and coinfection patterns of 13 key PRDC bacterial and viral pathogens. Our results revealed marked geographic, temporal, and production-stage variations. Glaesserella parasuis (56.7%), Streptococcus suis (56.4%), porcine reproductive and respiratory syndrome virus-1 (PRRSV-1) (52.4%), and Mesomycoplasma hyorhinis (47.8%) were the most frequently detected agents. Notably, the frequency of these secondary opportunists rose steadily until 2022 before decreasing in the following years, mirroring declines in primary PRDC pathogens such as PCV2 and Mesomycoplasma hyopneumoniae . Secondary opportunistic bacteria were predominantly detected in post-weaning piglets ( p <  0.05), while PRRSV-1 exhibited marked regional differences, with higher positivity in northeastern Spain ( p  < 0.05). Over 1,100 distinct coinfection patterns were identified, demonstrating the intricate dynamics of pathogen interactions. Co-occurrence networks and logistic regression analyses underscored robust associations. Notably, M. hyorhinis emerged as a pivotal pathogen, showing strong links with nine of the evaluated pathogens, including G. parasuis (OR = 4.05), S. suis (OR = 1.57), and PRRSV-1 (OR = 2.55). These findings underscore that effective PRDC control requires integrated diagnostic approaches and tailored preventive strategies, offering critical insights for developing targeted interventions to mitigate the multifactorial impact of PRDC on pig production both in Spain and globally.