Serological and Molecular Epidemiology of Viral and Bacterial Pathogens in Selected Commercial Pig Farms in Greece, 2024–2026

Consolidated, multi-pathogen, multi-year surveillance data are scarce for the Greek swine industry. We compiled a retrospective dataset from 55 diagnostic laboratory reports (2024–2026) covering 38 commercial farrow-to-finish pig farms across mainland Greece. Individual sera (n = 8272 valid ELISA results) were tested for antibodies against Aujeszky’s disease virus (gE), Mycoplasma hyopneumoniae, porcine reproductive and respiratory syndrome virus (PRRSV), porcine parvovirus, porcine circovirus type 2 (PCV2), Erysipelothrix rhusiopathiae, Actinobacillus pleuropneumoniae, and swine influenza A virus (swIAV), and 663 pooled blood samples were tested using real-time RT-PCR (PRRSV) or droplet digital PCR (PCV2). Associations with sampling year, age/production stage, and region were assessed using farm-clustered models. Seroprevalence was high for PCV2 (87.2%), PRRSV (80.4%), and porcine parvovirus (80.4%), moderate for A. pleuropneumoniae (56.0%), M. hyopneumoniae (50.9%), and swIAV (48.2%), lower for E. rhusiopathiae (34.3%), and very low for the Aujeszky’s disease gE marker (3.3%). Sows were routinely vaccinated against PRRSV, porcine parvovirus, E. rhusiopathiae, swIAV, and Aujeszky’s disease, and piglets against PCV2 and M. hyopneumoniae; for these agents, seroprevalence therefore largely reflects vaccination rather than natural exposure alone. Because the gE-deleted marker vaccine used in sows does not induce anti-gE antibodies, the low gE seroprevalence indicates limited field virus exposure. Seroprevalence differed significantly between age/production stages for every pathogen, whereas year and regional effects were not confirmed after small-sample-corrected adjustment for farm clustering. PRRSV RNA and PCV2 DNA were detected in 34.6% and 19.5% of pools, respectively; these results confirm the presence of viral nucleic acid in the tested pools but do not indicate the number of infected animals or, for PRRSV, distinguish field from vaccine virus. The dataset provides a quantitative baseline for comparable commercial farms rather than a nationally representative estimate.