Development of a PRRSV Detection Assay Using Multienzyme Isothermal Rapid Amplification and Genetic Analysis of PRRSV in Southwest China

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious viral disease that causes substantial economic losses in the swine industry. This study aimed to develop a PRRS virus (PRRSV) detection assay using multienzyme isothermal rapid amplification (MIRA) and to analyze the genetic variation of PRRSV in Southwest China. A total of 13,863 samples, including blood and lung tissues from pigs suspected of PRRSV infection, were collected. The MIRA assay was designed with primers and probes targeting conserved regions of the PRRSV-M gene, demonstrating high specificity with no cross-reactivity to other swine pathogens and an estimated detection threshold sensitivity of 1.0 copy/μL. Prevalence analysis revealed that, although vaccinated pigs showed relatively high antibody levels, the virus continued to circulate, particularly in unvaccinated herds. Genetic analysis of the predominant PRRSV strains indicated an increasing prevalence of NADC30-like strains and notable genetic variation in genes such as ORF5 and nonstructural protein 2 (NSP2), including amino acid deletions and alterations of glycosylation sites. Recombination events were also observed in some isolates. These findings provide essential insights into the epidemiology and genetic diversity of PRRSV in Southwest China, contributing critical data for the development of more effective control and prevention strategies.