Truck cleaning and disinfection, and the risk of PRRSV dissemination in multi-site pig production systems in the United States: A network-epidemiological model approach

Porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant threat to pig health, particularly in multi-site industrial pig farming systems. These systems, which involve raising pigs at different locations based on their age and transporting them via trucks and trailers, may increase the risk of pathogen transmission through contaminated vehicles. Given the importance of preventing PRRSV infection, vehicle cleaning and disinfection (C&D) are crucial for disease control. This study examined data from four PRRSV outbreaks in U.S. sow farms during a regional emergence of a PRRSV2 variant in multi-site swine production systems, focusing on vehicle movements before and after the outbreaks and their C&D frequencies. This research analysed 1190 vehicle movement records between premises and 753 visits to truck wash stations, creating networks encompassing seven vehicles across 45 sites, including breeding, growing, and isolation facilities. Network simulations were used to evaluate the infection sources and virus transmission risks under various vehicle C&D frequencies during outbreaks. Results showed no significant changes in movement frequency before and after the outbreak. The infection risk varied by farm type and specific connections to the outbreak farm, with higher risks observed in growing farms. Scenario comparisons to assess the impact of C&D frequencies on transmission showed that adherence to vehicle C&D protocols resulted in infection risks nearly matching optimal scenarios. The most substantial differences were observed when comparing infection probabilities in the pessimistic scenario to those in the realistic scenario, with probabilities being significantly higher in the pessimistic scenario, particularly for gilt isolation farms (7.6 % higher) and sow farms (6.6 % higher). These findings underscore the critical role of thorough cleaning and disinfection protocols in reducing infection risk.This research assesses the risks of infection introduction and spread during outbreaks, emphasising the critical role of truck washing in controlling PRRSV. The study provides quantitative evidence that consistent vehicle C&D practices significantly reduce transmission risks, offering valuable insights into disease transmission pathways. These findings inform targeted interventions to enhance biosecurity and strengthen disease prevention strategies.