Since its recent appearance in China, the NADC30-like strains of porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) have caused an expanding epidemic, and this has further expanded the genetic diversity of PRRSV. In this study, three NADC30-like strains—GXFCG20210401, GXQZ20210403 and GXNN20210506—were isolated from pig serum samples obtained in Guangxi, and their genomes were sequenced. A comparative analysis of the whole genomes showed that the three strains were most similar to NADC30 (88.3–88.7%). In particular, the non-structural protein coding regions (nsp1, nsp4-5, nsp7-8 and nsp9) showed the highest similarities to JXA1, and the ORF2a-ORF5 regions showed the highest similarities to NADC34. The three strains had same discontinuous deletions of 111+1+19 amino acids in the nsp2 region, which were similar to the NADC30-like strains. Phylogenetic tree analysis based on the ORF5 gene showed that the three PRRSV isolates were divided into lineage 1.5 along with the representative NADC34-like strains, but they were classified as NADC30-like strains with respect to the whole genome and nsp2 evolutionary trees. Recombinant analysis revealed complex recombination patterns in the genomes of the three strains, which likely originated from multiple recombination events among JXA1-like, NADC30-like and NADC34-like strains. The results from animal experiments showed that the GXQZ20210403 strain was 20% lethal to piglets and caused more severe clinical reactions than GXFCG20210401, and both recombinant strains were similar in terms of pathogenicity to the previously reported NADC34 strains. This study demonstrates that NADC34-like strains of PRRSV have been circulating in the southern provinces of China and have exchanged genomes with several other indigenous strains. In addition, differences in recombination patterns may cause different clinical pathogenicity and indicate the importance of the surveillance and preventive control of recombinant strains.

Porcine epidemic diarrhea virus (PEDV) is a major enteric pathogen of swine, and the spike (S) protein determines how the virus enters cells. Coronaviruses enter either at the plasma membrane or through endosomes, but whether variation in S switches the route itself and how this relates to cell and tissue tropism is unclear. In this study, we generated isogenic recombinant PEDVs differing only in S by introducing the S genes of the cell culture-adapted G1b strain SD and the virulent G2b strain FJzz1 into the G2b strain HM backbone. rPEDV-HM-S_HM and rPEDV-HM-S_FJzz1 required exogenous trypsin for infection, whereas rPEDV-HM-S_SD infected Vero cells efficiently without trypsin, and the three viruses differed in cell tropism. rPEDV-HM-S_SD infected BHK-21, Huh7, JHH7, and Vero cells most efficiently but failed to infect IPEC-J2 cells and porcine intestinal organoids, which the two trypsin-dependent chimeras infected. The cathepsin inhibitor E64d blocked rPEDV-HM-S_SD but not the trypsin-dependent viruses, whereas the serine protease inhibitor camostat blocked the trypsin-dependent chimeras but not rPEDV-HM-S_SD. Furthermore, WDR81 was required preferentially by rPEDV-HM-S_SD. Collectively, PEDV S protein determines protease dependence, cell tropism, and entry route, and cell culture adaptation redirects entry to an endosomal pathway that no longer supports infection of the natural target tissue.

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) continues to pose a substantial threat to the global swine industry, with recombination-driven evolution generating novel variants that complicate disease control. In this study, two novel recombinant PRRSV-2 strains, designated GXNN202004a and GXGG20210301, were isolated from PRRS-affected pig farms in southern China. Whole-genome sequencing and phylogenetic analysis revealed that both strains possess an NADC30-like backbone, with GXNN202004a arising from recombination between NADC30 and JXA1 and GXGG20210301 representing a multi-lineage recombinant derived from NADC30, JXA1, and QYYZ. Genomic characterization identified a characteristic discontinuous 131-amino-acid deletion (111+1+19 aa) in the NSP2 coding region, along with a previously unreported six-amino-acid deletion in GXGG20210301. Animal pathogenicity assays demonstrated that both strains induced moderate clinical signs, including persistent fever, respiratory symptoms, and growth impairment, without causing mortality in piglets. Viral loads were detectable in multiple tissues, serum, and nasal swabs, indicating broad organ tropism and shedding potential. These findings enrich the molecular epidemiological data on PRRSV in China, highlight the increasing genetic diversity and recombination complexity of circulating strains, and provide scientific evidence for improved PRRS surveillance and vaccine development strategies in southern China.