Circulation and Spillover of pdmH1N1 Influenza A Virus at an Educational Swine Farm in Chile, 2019-2023

Educational farms provide students with hands-on experience in agricultural and animal practices. However, the close contact between humans and farm animals creates a significant interface for zoonotic disease transmission, yet research on infectious diseases in such settings remains limited. This study investigates the ongoing spillovers of human-origin influenza A virus (IAV) into swine at an educational farm in central Chile, describing IAV prevalence, outbreak dynamics, and the genomic characterization of detected strains. The Menesianos educational farm, located in Melipilla, central Chile, houses approximately 40 swine alongside other domestic animals, such as horses and cows. As part of an active IAV surveillance project, monthly nasal swab samples were collected from pigs between June 2019 and September 2023 for IAV detection via RT-qPCR targeting the M gene, with positive samples subsequently sequenced. During the study period, monthly IAV prevalence ranged from 0% to 52.5%, with a notable outbreak detected between May and June 2023. The outbreak lasted 5 weeks, peaking at 52.5% prevalence during week 3. Nine IAV strains were isolated over the study period, eight of which were obtained during weeks 2 and 3 of the outbreak. Phylogenetic analysis revealed that all strains were closely related to the pandemic H1N1 2009 influenza virus, with the closest related strains being those circulating in humans in Chile during the same years. These findings highlight the importance of conducting regular IAV surveillance on educational farms, where close interactions between animals and individuals-particularly children and young people-can facilitate viral spillovers and potential reverse zoonosis events.