CDC Since the 2009 swine influenza pandemic, sporadic human infections with swine influenza A viruses (swIAVs) continue to occur, including rare instances of onward human-to-human transmission, highlighting the ongoing pandemic risk (1–4). Pigs are key reservoirs and mixing vessels for influenza A virus (IAV) evolution; transmission between humans and pigs is frequent and bidirectional (5,6). Active epidemiologic and genomic surveillance at the swine–human interface is therefore essential for early detection and risk assessment of emerging strains.
In Switzerland, pig production is less intensive; herds remain relatively isolated from neighboring countries because of strict regulations and minimal import of live pigs (7,8). Infrequent use of swIAV vaccines allows for natural viral evolution without vaccine-driven selective pressures (9); country-specific transmission chains may exist within pig herds in Switzerland. The ongoing national surveillance program for swIAV relies primarily on partial hemagglutinin (HA) and neuraminidase (NA) gene sequences, limiting its ability to identify emerging swIAV lineages in pig herds (10).
To investigate the epidemiology and genetic diversity of swIAV in pig herds, we established a whole-genome sequencing (WGS)–based swIAV surveillance program. We obtained samples from symptomatic and randomly selected pig herds; pig caretakers with respiratory illness voluntarily provided self-collected nasal swab specimens. Here, we report a zoonotic transmission event involving Eurasian avian-like (EA) swine influenza A(H1N1) virus detected concurrently in a farmer and his pig herd through WGS surveillance.