Novel L1A/C RFLP 1-3-4 porcine reproductive and respiratory syndrome virus causing severe intestinal infections in...

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), is one of the most economically significant swine diseases globally. In recent years, Lineage 1 (L1) PRRSV strains, including RFLP 1-3-4, RFLP 1-4-4, and RFLP 1-7-4, have emerged and spread widely in the United States, whereas the L1 RFLP 1-3-4 strain has been relatively rarely reported in China. In this study, three novel recombinant PRRSV variants, named TJ2401 (lineages 1.5, 1.8, and 8) with an L1A RFLP 1-3-4 pattern, TJ2402 (lineages 1.8 and 8) with an L1C RFLP 1-3-4 pattern and L1C TJ2406 (lineages 8.1, 8.2, and 1.8), were isolated from three distinct local pig farms in China in 2024. Experiments on 6-week-old piglets have demonstrated that the three isolated strains can induce severe interstitial pneumonia. Notably, both the TJ2401 strain and the TJ2402 strain exhibiting the RFLP 1-3-4 pattern can elicit typical clinical symptoms of diarrhea. Concurrently, high viral loads were detected in their fecal samples, aligning with the clinical signs of diarrhea. However, the TJ2406 isolated strain did not manifest typical diarrhea symptoms. Based on clinical observations and pathogenicity experiments, we have confirmed that these novel L1A/C 1-3-4 variants exhibit extensive tissue tropism, particularly in intestinal tissues. These results indicate the urgent need for comprehensive epidemiological surveillance and the development of new strategies to prevent the further spread of the disease.