Recent advances in the study of NADC34-like porcine reproductive and respiratory syndrome virus in China

Abstract

Since porcine reproductive and respiratory syndrome virus (PRRSV) was first described in China in 1996, several genetically distinct strains of PRRSV have emerged with varying pathogenicity and severity, thereby making the prevention and control of PRRS more difficult in China and worldwide. Between 2017 and 2021, the detection rate of NADC34-like strain in China increased. To date, NADC34-like strains have spread to 10 Chinese provinces and have thus developed different degrees of pathogenicity and mortality. In this review, we summarize the history of NADC34-like strains in China and clarify the prevalence, genomic characteristics, restriction fragment length polymorphisms, recombination, pathogenicity, and vaccine status of this strain in China. In so doing, this study aims to provide a basis for the further development of prevention and control measures targeting the NADC34-like strain.

Keywords: NADC34-like; PRRSV; RFLP; pathogenicity; recombination.

FIGURE 1

Distribution of NADC34-like strains worldwide and in China. Maps show the four countries and 10 Chinese provinces where NADC34-like strains have been identified to date: China, the United States, Peru, and South Korea. On the world map, countries known to harbor NADC34-like strains are colored red. On the map of China, provinces known to harbor NADC34-like strains are colored blue, with color intensity increasing with the number of unique NADC34-like strains identified. HLJ, Heilongjiang Province; JL, Jilin Province; LN, Liaoning Province; TJ, Tianjin City; HB, Hebei Province; SD, Shandong Province; HN, Henan Province; JS, Jiangsu Province; FJ, Fujian Province; SC, Sichuan Province. Maps were obtained from yourfreetemplates.com.

FIGURE 2

Phylogenetic tree based on the whole-genome and ORF5-gene sequences of NADC34-like strains from China. (A) Phylogenetic analysis of NADC34-like strains in China and reference viruses based on whole-genome sequences. (B) Phylogenetic analysis of NADC34-like strains in China and reference viruses based on ORF5-gene sequences. Most of the NADC34-like strains isolated in China belonged to Sublineage 1.5, but a few recombinant strains fell into Sublineage 1.8. The phylogenetic tree was constructed using the distance-based neighbor-joining algorithm in Mega7 (Kumar et al., 2016), with 1,000 bootstrap replicates (▲ indicates the reference virus).

FIGURE 3

Alignment of Nsp2 amino acid sequences. Most of the NADC34-like strains isolated in China have a continuous deletion of 100 aa, which corresponds to positions 348–427 in Nsp2 from the reference strain VR2332 (boxed in red). The strains that recombine at the Nsp2 position differ (boxed in green). Amino acids were aligned using the MegAlign tool in Lasergene software (DNASTAR Inc., Madison, WI, United States).

FIGURE 4

Restriction fragment length polymorphisms (RFLPs) in the ORF5 gene of NADC34-like strains in China. Some RFLPs in ORF5 had not previously been associated with HincII digestion. These patterns were artificially divided into patterns 9 and 10. The number of RFLP patterns identified in Chinese NADC34-like strains, as well as the relative abundances of patterns 1-4-4 and 1-7-4, increased between 2017 and 2021. The relative abundances of patterns 1-6-4 and 1-10-4, which were only reported recently, have also increased gradually. This graph was produced using Graphpad Prism V 7.03 (GraphPad Software Inc., San Diego, CA, United States).

FIGURE 5

Schematic diagram of the recombination of HLJTZJ2165-2108, LNDZD10-1806, and HLJTZJ1988-2106 strains. (A) Origin of HLJTZJ2165-2108 strain. (B) Origin of strains LNDZD10-1806 and HLJTZJ1988-2106. Maps produced using Adobe Illustrator CC 2019 (Adobe Inc., San Jose, CA, United States).