Porcine circoviruses (PCVs) are notorious for triggering severe diseases in pigs and causing serious economic losses to the swine industry. In the present study, we undertook a comprehensive approach for the investigation of PCV prevalence, including the phylogenetic analysis of obtained PCV sequences, the determination of major circulating genotypes and serological screening based on different recombinant Cap proteins with specific immunoreactivity. Epidemiological surveillance data indicate that PCV2d and PCV3a are widely distributed in Southwest China, while PCV4 has only sporadic circulation. Meanwhile, serological investigations showed high PCV2 antibody positivity in collected serum samples (>50%), followed by PCV4 (nearly 50%) and PCV3 (30–35%). The analysis supports different circulation patterns of PCV2, PCV3 and PCV4 and illustrates the PCV2/PCV3 genetic evolution characteristics on a nationwide basis. Taken together, our findings add up to the current understanding of PCV epidemiology and provide new tools and insight for PCV antiviral intervention.

Porcine epidemic diarrhea virus (PEDV) is a major pathogen that causes serious economic losses to the swine industry. To aid PEDV clinical diagnosis and vaccine development, sensitive and precise serological methods are demanded for rapid detection of (neutralizing) antibodies. Aiming for the development of a novel virus-free hemagglutination inhibition (HI) assay, the N-terminal region of the PEDV S1 subunit, encompassing the sialic acid-binding motif, was first expressed as an Fc-fusion protein with a C-terminal Spy Tag (S1^0A-Spy). The S1^0A-Spy protein was then presented on SpyCatcher-mi3 nanoparticles, forming virus-like particles designated S1^0A-NPs. Electron microscopy and dynamic light scattering analysis confirmed its topology, and the hemagglutination assay showed that S1^0A-NPs can efficiently agglutinate red blood cells. The HI assay based on S1^0A-NPs was then validated with PEDV-positive and -negative samples. The results showed that the HI assay had high specificity for the detection of PEDV antibodies. Next, a total of 253 clinical serum samples were subjected to the HI testing along with virus neutralization (VN) assay. The area under the receiver operating characteristic curve with VN was 0.959, and the kappa value was 0.759. Statistical analysis of the results indicated that the HI titers of the samples tested exhibited high consistency with the VN titers. Taken together, a novel virus-free HI assay based on the multivalent display of a chimeric PEDV spike protein upon self-assembling nanoparticles was established, providing a new approach for PEDV serological diagnosis.