A novel circovirus called porcine circovirus type 4 (PCV4) was recently detected in pigs suffering from severe clinical diseases in Hunan province, China. There are few reports on the origin and evolution of PCV4, although some researchers have conducted epidemiological investigations of PCV4 and found that PCV4 is widespread in pigs. Based on the previous study, we detected PCV2 in farmed foxes and raccoon dogs with reproductive failure. To explore whether the PCV4 genome also exists in fur animals, we detected 137 cases admitted from fur animal farms in Hebei China between 2015 and 2020, which were characterized by inappetence, lethargy, depression, abortion, and sterility. The overall infection rate of PCV4 was 23.36% (32/137), including 20.37% (22/108) for raccoon dogs, 18.75% (3/16) for foxes, and 53.85% (7/13) for minks. Finally, five raccoon dog-origin PCV4 strains and one fox-origin PCV4 strain were sequenced in our study, whose nucleotide identities with other representative PCV4 strains varied from 96.5% to 100%. Phylogenetic analysis based on the complete genomes of PCV4 strains indicated a close relationship with those of PCV4 strains identified from pigs. To our knowledge, this is the first study to detect PCV4 in fur animals. Interestingly, we also identified PCV4 in a mixed farm (feeding pigs and raccoon dogs at the same time). In summary, our findings extend the understanding of the molecular epidemiology of PCV4 and provide new evidence for its cross-species transmission.

Porcine Transmissible Gastroenteritis Virus (TGEV) is widespread and frequently involved in co-infections, leading to high mortality rates in piglets and s

Porcine epidemic diarrhea virus (PEDV) causes severe mortality in piglets, inflicting significant economic losses globally. Nanobodies (Nbs) offer distinct advantages over conventional antibodies for disease intervention. This study aimed to develop neutralizing Nbs against the PEDV spike (S) protein. We constructed a eukaryotic plasmid encoding the S protein of the CH-HB2-2018 strain and expressed it in HEK-293 F cells. Following alpaca immunization with the purified S protein, a phage display library was constructed. Biopanning yielded 70 unique Nbs based on CDR diversity, with 67 confirmed as specific binders via ELISA and Western blot. Further characterization using immunofluorescence and flow cytometry identified 9 specific candidates. Microneutralization assays revealed that these candidates showed varying degrees of inhibition against PEDV replication in Vero cells. Notably, nanobody 3Nb17 exhibited the highest binding affinity and neutralizing titer. These findings highlight 3Nb17 as a promising candidate for developing novel PEDV diagnostic tools and therapeutics.