# Etiological Detection, Isolation, and Pathogenicity of Porcine Reproductive and Respiratory Syndrome Virus in China

## TL;DR

This study identifies and characterizes the most prevalent PRRSV strains in China, highlighting their genetic diversity and pathogenicity for better disease control.

## Contribution

The study isolates and characterizes two novel PRRSV strains, JX03 and HN08, and evaluates their pathogenicity in pigs.

## Key findings

- NADC30/34-like PRRSV is the dominant strain in China, followed by highly pathogenic PRRSV.
- JX03 showed the highest pathogenicity, while HN08, a recombinant strain, showed the lowest.
- HN08 is a recombinant of NADC30-like and NADC34-like strains, with no recombination in JX03.

## Abstract

Porcine reproductive and respiratory syndrome (PRRS) is a global widespread infectious disease that severely impacts the swine industry. The high genetic variability of the PRRS virus (PRRSV) has led to the continuous emergence and spread of novel strains. The surveillance of PRRSV epidemiology and isolation of circulating strains are crucial for developing effective PRRSV control strategies. In this study, we confirmed that NADC30/34-like PRRSV is the dominant epidemic strain in China, followed by highly pathogenic PRRSV (HP-PRRSV). An HP-PRRSV strain (JX03) and a recombinant NADC34-like PRRSV strain (HN08) were isolated, and their whole genome and phylogenetic characterization were analyzed. Animal experiments confirmed that the JX03 strain exhibited the highest pathogenicity, followed by CHN-HB-2018 (a NADC30-like PRRSV strain previously isolated by our lab), while HN08 demonstrated the lowest pathogenicity. These findings provide critical information for PRRSV molecular epidemiology and vaccine strain selection.

Due to its high genomic variability, the epidemiological landscape of porcine reproductive and respiratory syndrome virus (PRRSV) has become increasingly complex in recent years. From 2022 to 2023, we collected a total of 1044 clinical samples from pigs suspected of PRRSV infection in China and discovered a PRRSV-positive rate of 29.8% (311/1044) using RT-PCR targeting the nsp2 gene. Among these positive samples, NADC30/34-like PRRSV, highly pathogenic PRRSV (HP-PRRSV), and classical PRRSV strains accounted for 60.1%, 37.9%, and 4.5%, respectively. These results indicate that the most prevalent PRRSV strains in China are NADC30/34-like PRRSV, followed by HP-PRRSV. Two PRRSV strains, JX03 and HN08, were isolated, and TCID50 assays were performed to determine their titers at different time points post-infection, revealing differences in their proliferation kinetics. Phylogenetic, amino acid sequence, and recombination analyses demonstrated that the JX03 and HN08 strains cluster within lineage 8 (HP-PRRSV) and sublineage 1.5 (NADC34-like PRRSV), respectively. Notably, the HN08 strain was identified as a recombinant between the NADC30-like and NADC34-like strains, while no recombination event was detected in the JX03 strain. Pathogenicity assessments showed that the JX03 strain exhibited higher pathogenicity than the CHN-HB-2018 strain (a NADC30-like PRRSV strain was previously isolated by our lab), as evidenced by differences in clinical signs and mortality rates in piglets. In contrast, HN08 displayed no obvious clinical symptoms or mortality, revealing lower pathogenicity than the CHN-HB-2018 strain. These findings provide valuable information on the epidemiological and genetic characteristics of PRRSV strains in China, laying a foundation for the development of effective strategies against PRRSV.