Prevalence and viral load dynamics of PCV-2 and PCV-3 on large Hungarian swine farms

Porcine Circovirus 3 (PCV-3) was first identified in 2016 and has since been detected in swine herds worldwide. The aim of this study was to survey the prevalence of PCV-2 and PCV-3 in large Hungarian swine herds. Between July 2020 and April 2022, a total of 1,408 blood samples were collected from 18 large herds and pooled sampling was applied by combining equal amounts from five individuals per pool. PCV-3 positive samples were detected in 94.4% (17/18) of the farms, with an overall apparent prevalence of 30.4% (89/293) in the tested pools. PCV-2 was found in 50.0% (9/18) of the farms, with 14.7% (43/293) of pools testing positive. After correction for imperfect PCR sensitivity and specificity (assumed to be 95%), the corrected prevalence of PCV-3 was 28.2% (83/293) and 10.7% (32/293) for PCV-2, farm-level prevalence estimates remained unchanged. Quantitative PCR analysis revealed that 24.2% of the PCV-3-positive pools had low (Cq > 30), 5.8% medium (28 < Cq < 30) and 1.0% high viral loads (Cq < 28). These results confirm that PCV-3 is widely present in large Hungarian swine farms. The relatively high prevalence, viral load and frequent co-infections raise the possibility of subclinical infections, although the clinical significance of PCV-3 requires further investigation.