company news about Harbin Veterinary Research Institute: Current Prevalence of NADC30-like and 12 Recombinant Models

In 2012, the PRRSV-like NADC30 strain was first discovered in my country. Since 2016, this strain has gradually become the predominant strain in the country. Currently, this strain exhibits a highly complex recombination pattern, characterized by low genome sequence homology. It exhibits moderate clinical symptoms, possesses strong immunosuppressive properties, and induces a weak antibody response, presenting new epidemic characteristics.

Recently, the Harbin Veterinary Research Institute of the Chinese Academy of Agricultural Sciences and Nanyang Normal University published a study online in Porcine Health Management on the genomic characteristics and epidemic trends of NADC30-like PRRSV in my country, providing data support for related epidemiological research and prevention and control.

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) has caused severe economic losses to my country's swine industry. In 2012, NADC30-like PRRSV was first discovered in my country. For many years, Tian Zhijun's team at the Harbin Veterinary Research Institute has continuously monitored the epidemic situation of PRRSV in my country.

Research Results

1. Significant Increase in NADC30-like Recombinations

Studies have shown that since 2016, NADC30-like PRRSV has become the predominant strain in my country. To further understand its prevalence in China, researchers used next-generation sequencing technology to obtain the whole genome sequences of 30 virus strains. Combined with sequences from 224 Chinese strains in the GenBank database, their genomic characteristics were systematically analyzed. The results showed that the number of recombinant strains increased year by year, and non-recombinant strains have almost disappeared. Among them, L1C+L8E, L1C+L5A and L1C+L1A+L8E are currently the three most common recombinant types.

Figure 1. Epidemiology and Recombination of NADC30-like PRRSV in China

(A) Prevalence of PRRSV in China, (B) Temporal Trends of Recombinant Strain Patterns

(C) Distribution of Recombination Patterns

Conclusion: In recent years, NADC30-like strains have continued to dominate in my country and have extensively participated in recombination, forming multiple subtypes, with L1C+L8E being the most common. Whole-genome sequencing has become a key tool for studying their evolution and pathogenicity.

2. 12 Recombination Models

With the increasing number of recombinant strains, typing based solely on the ORF5 gene is no longer able to fully and accurately reflect viral characteristics. This study used phylogenetic analysis based on whole-genome sequences and combined recombination results to classify NADC30-like strains in my country. Ultimately, 120 strains with similar recombination characteristics were classified into 12 subtypes, NADC30-R1 to R12. The average genetic distance within subtypes was 5.73% (standard deviation ±1.68), while the genetic distance between subtypes generally exceeded 10%. All strains in the same group had a discontinuous deletion of 131 amino acids in the Nsp2 protein, consistent with the typical characteristics of NADC30-like strains. In terms of virulence, the strains in each group showed no significant consistency, with most strains being of moderate virulence.

Figure 2. Classification system of NADC30-like PRRSV based on phylogenetic analysis and recombination patterns

(A) Whole-genome phylogenetic tree, (B) Recombination pattern genome map

Conclusion: This study classified Chinese NADC30-like strains into 12 types through whole-genome analysis. These strains were found to exhibit a typical Nsp2 deletion, with moderate virulence and significant genetic variation within the group.

3. Whole-genome sequences from 19 provinces

The results showed that whole-genome sequences of NADC30-like viruses from 19 provinces in my country revealed a gradual increase in the number of strains belonging to the NADC30-R1 to R12 types since 2018, with NADC30-R1 and NADC30-R2 representing a significant proportion. The NADC30-R1 strain first appeared in 2014 and has been circulating for a long time, with recent reports still ongoing. The NADC30-R2 strain is the most widely distributed NADC30-like virus in my country, having spread to at least 12 provinces and regions. After its first appearance in 2020, it spread rapidly, with its detection rate increasing significantly in recent years. Although the recombination patterns of NADC30-like strains are complex, some strains of the same recombinant type have become prevalent in parts of China.

Figure 3. Geographical Distribution and Proportion of NADC30-like PRRSV Whole-Genome Sequences in Each Group

(A-B) Geographical Distribution of Strain Types, (C) R1/R2 Dominance

Conclusion: Among NADC30-like viruses in my country, the number of R1 and R2 strains is increasing. In particular, the widespread and rapidly spreading R2 strain exhibits complex recombination patterns and continues to circulate in some areas.

4. Proportion of Recombinant Strains

The epidemic situation of NADC30-like PRRSV in my country remains complex, with the continuous emergence of new recombinant strains increasing the genetic diversity of the virus. Notably, NADC30-IR remains the largest group, and the recombination patterns within this group are quite diverse and lack consistent characteristics. As the number of whole-genome sequences in the GenBank database increases, new characteristic strains may be discovered in the future, or they may be reclassified into the existing NADC30-R1 to R12 types.

Figure 4. Proportion of NADC30-like PRRSV with different recombination patterns in China

NR: non-recombinant strain; IR: strain with irregular recombination pattern; R1 to R12: recombinant strains with consistent characteristics. The X-axis represents the classification criteria used in this study. The Y-axis represents the sample size for each type.

Conclusion: The epidemic situation of NADC30-like PRRSV in my country is complex, with increasing genetic diversity. NADC30-IR is the dominant group. New strains may emerge or the existing classification may be adjusted as more data becomes available.

Summary

This study shows that the PRRSV-2 currently circulating in my country is primarily composed of the L1A, L1C, L3.5, and L8E sublineages, of which L1C (NADC30-like) is dominant and frequently recombines. Recombination promotes viral diversification and evolution, but recombination does not directly determine virulence; virulence is associated with specific recombination patterns.