Isolation and pathogenicity of a highly virulent recombinant GIIc subtype PEDV strain

Porcine epidemic diarrhoea virus (PEDV) is a highly contagious enteric coronavirus causing acute watery diarrhoea and high mortality in neonatal piglets, threatening the global swine industry. In recent years, GIIc subtype PEDV has spread rapidly across China via natural recombination and antigenic drift, undermining conventional vaccine efficacy. Here, we isolated and characterized a novel GIIc PEDV strain CHjx2025 from diarrheic piglets in Ji'an City, Jiangxi Province, China. Full-length genome sequencing and recombination analysis identified CHjx2025 as a natural intra-lineage recombinant of two GIIc strains (CH-JXJA-2017 as major parent and CH-SWM-RN-2025 as minor parent), with a recombination breakpoint at nucleotide 11,201 of ORF1a. Comparative analysis revealed 49 unique amino acid substitutions in the spike (S) protein core region relative to the classic vaccine strain CV777, including 10 in the core receptor-binding domain (COE) and 1 in the 2C10 neutralizing epitope. Structural modeling confirmed CHjx2025 retains a canonical homotrimeric type I fusion protein structure but exhibits distinct NTD and D0 domains versus CV777. In vitro, CHjx2025 showed strong replicative capacity, forming larger plaques and reaching 10^6.5TCID₅₀/mL in Vero cells at 24 hpi. Notably, in vivo challenge induced vomiting and anorexia in neonatal piglets as early as 12 hpi, with 100% mortality within 60 h, severe intestinal villous atrophy, and unprecedented multinucleated syncytia in intestinal epithelial cells. These findings highlight the evolving diversity and enhanced pathogenicity of GIIc PEDV via intra-subtype recombination and epitope mutations, underscoring the need for continuous surveillance and GIIc-specific vaccine development to control PED outbreaks.