Whole-genome characterization and pathogenicity of novel human-porcine reassortant rotavirus strains G9P[7] and G1P[7] in China

The prevalence of porcine rotavirus A (PoRVA) in China has increased significantly, threatening the swine industry. Pigs serve as “mixing vessels” for rotaviruses, facilitating reassortment between human and animal strains, leading to the emergence of zoonotic variants. In this study, two PoRVA strains, XXW2023 (G9P[7]) and HD2023 (G1P[7]), were isolated from diarrheic piglets in Guangdong Province, China. Genomic analysis revealed that both strains were human-porcine reassortants, with VP1, VP3, and NSP1 genes closely related to human rotaviruses. Intragenic recombination was identified in the VP4 and VP6 genes. Pathogenicity was evaluated in 7-day-old mice and 1-day-old piglets. Both strains caused persistent diarrhea in mice and severe watery diarrhea, intestinal lesions, and death within 48 h in piglets. Systemic infection was confirmed, with viral replication detected in the lungs. Infectious virus titers, VP6 antigen, and NSP4 were detected in lung tissues, providing evidence of active replication in the respiratory tract. The strains exhibited distinct tissue tropism, with XXW2023 being enterotropic and HD2023 showing pulmonary tropism. Viral RNA and antigen levels in the lungs of HD2023-infected piglets exceeded those in their intestines, and the infectious virus titer in their lungs was significantly higher than that in the lungs of XXW2023-infected piglets. These findings demonstrate that reassortant rotavirus strains infect the respiratory tract, extending the conventional view of rotavirus as a strictly enteric pathogen. The emergence of these highly pathogenic, phenotypically divergent human-porcine reassortants underscores their zoonotic risk, highlighting the need for enhanced surveillance and reconsideration of vaccine coverage.