# Emergence and Pathogenicity of a Novel PRRSV-1 Strain GD18-2 in Southern China

## TL;DR

A new strain of PRRSV-1 called GD18-2 is causing serious illness in pigs in China, even in vaccinated herds, and can be passed from mother pigs to their unborn offspring.

## Contribution

The study identifies and characterizes GD18-2, a novel PRRSV-1 strain with unique genetic features and high pathogenicity in southern China.

## Key findings

- GD18-2 has a unique genome with 81.4% to 83.9% nucleotide identity to classical PRRSV-1 strains.
- The strain causes severe respiratory disease and mortality in piglets and reproductive failure in pregnant sows.
- GD18-2 exhibits a deletion in Nsp2 and mutations in GP3 and GP4, distinguishing it from other PRRSV-1 strains.

## Abstract

A pig disease caused by the Porcine Reproductive and Respiratory Syndrome Virus type 1 is becoming more common in China, making it harder to control outbreaks on farms. In this study, we investigated a new strain of this virus, GD18-2, found on a pig farm in Guangdong that had vaccinated its animals against a related virus type. Our goal was to understand how this new strain is different and how harmful it is to pigs. We found that GD18-2 has a unique genetic makeup that sets it apart from previously known strains. When tested in young pigs, it caused severe breathing problems, fever, and some deaths. In pregnant mother pigs, it did not make the mothers very sick, but it spread to the unborn piglets, causing many to be born dead or very weak. These results show that this new virus strain poses a serious threat to pig health and farm productivity, especially because it can spread from mother to offspring before birth. Our work highlights the need for closer monitoring and updated prevention strategies to protect pigs from this emerging virus.

The detection rate of Porcine Reproductive and Respiratory Syndrome Virus type 1 (PRRSV-1) in China has been increasing, with its growing genetic diversity and evolving pathogenicity posing significant challenges to disease control. In this study, a novel PRRSV-1 strain, designated GD18-2, was identified from a pig farm in Guangdong Province that experienced an outbreak despite vaccination with a PRRSV-2 vaccine. Whole-genome sequencing indicated that the GD18-2 strain possesses a genome length of 14,932 bp and exhibits 81.4% to 83.9% nucleotide identity with classical PRRSV-1 strains. Phylogenetic analyses based on both the complete genome and the ORF5 gene indicated that GD18-2 belongs to a distinct, new lineage. A unique amino acid deletion (positions 306–357) was identified in the non-structural protein Nsp2, along with specific mutations within the hypervariable regions of the structural proteins GP3 and GP4. Pathogenicity assessment demonstrated that GD18-2 induced fever, respiratory symptoms, and mortality in piglets. In pregnant sows, it caused reproductive failure (abortion, stillbirth, weak piglets) and was capable of vertical transmission via the placenta. This study highlights the emergence of a PRRSV-1 strain with a unique genetic background and high pathogenicity in southern China, underscoring the necessity for enhanced molecular epidemiological surveillance and updated control strategies. Recombination analysis using RDP4 revealed no significant recombination events in GD18-2.