International Journal of Molecular Veterinary Research, 2025, Vol.15, No.1, 32-42 http://animalscipublisher.com/index.php/ijmvr 33 providing broad or long-lasting protection due to antigenic heterogeneity among field strains. In addition, molecular processes of viral replication, immune modulation, and persistence remain poorly understood. The emergence of highly pathogenic and recombinant PRRSV strains has also underscored continuous molecular surveillance and additional research into host-virus interactions. Such challenges underline the need for interdisciplinarity integrating virology, immunology, genomics, and epidemiology (Zhou et al., 2024). This study provides an overview of pathogenesis of PRRSV and recent advances in molecular diagnosis. It presents up-to-date information on viral structure, genetic variation, modes of infection, and immune evasion mechanisms, and reviews diagnostic advances in tools such as serological tests, nucleic acid detection, and next-generation sequencing. It also emphasizes key research challenges, the shortcomings of current diagnostic systems, and implications for prevention and control of molecular epidemiology. With a holistic perspective, this book places emphasis on the scientific and practical relevance of advancing PRRSV research for sustainable swine health management. 2 Biological Characteristics of PRRSV 2.1 Viral classification and genome structure Porcine reproductive and respiratory syndrome virus (PRRSV) is a Betaarterivirus, family Arteriviridae, order Nidovirales, single-stranded, positive-sense RNA virus. Genome size is approximately 15 kb with a minimum of 11 open reading frames (ORFs): ORF1a and ORF1b possess replicase polyprotein coding abilities, and ORF2a, ORF2b, ORF3-7, and ORF5a possess structural protein coding abilities. It is flanked by 5′ and 3′ untranslated regions (UTRs) and a poly(A) tail (Guo et al., 2021; Kim et al., 2022; Yuan et al., 2025). 2.2 Functions of major structural and non-structural proteins Structural proteins including GP2, GP3, GP4, GP5, M, N, E, and ORF5a. GP5 is the envelope glycoprotein with primary significance and a primary target for neutralizing antibodies, and M and N are essential for virion assembly. Immune evasion and virus entry are linked with minor glycoproteins (GP2, GP3, GP4) and E protein (Cui et al., 2024). Non-structural proteins (NSPs) such as NSP2, NSP7, and NSP9 are involved in viral replication, pathogenicity, and host immunity regulation. NSP2 is the most variable protein and is involved in maturation of viral proteins, assembly, and immune regulation; NSP9 is the RNA-dependent RNA polymerase required for replication; NSP7 is a highly conserved protein important for replication and immunity (Li et al., 2023; Liu et al., 2023). 2.3 Viral variation, recombination, and genotypic classification (PRRSV-1 and PRRSV-2) PRRSV has two large genotypes: PRRSV-1 (European type, Betaarterivirus suid 1) and PRRSV-2 (North American type, Betaarterivirus suid 2), and they are differentiated by only around 60%-70% nucleotide identity (Wang et al., 2020; Kim et al., 2022). Both genotypes also get split into different lineages and subtypes based on ORF5 and whole-genome phylogenies. PRRSV exhibits great genetic variability due to high rates of point mutations, insertions/deletions (especially in NSP2), and excessive recombination. Recombination hotspots exist in NSP9, GP2-GP3, and other places, generating new, at times extremely virulent, recombinant strains (Xing et al., 2022). 2.4 Genetic diversity and epidemiological trends of PRRSV PRRSV is highly genetically heterogeneous with more than a single lineage co-circulating and frequent emergence of new variants. Both PRRSV-1 and PRRSV-2 circulate in China and elsewhere where PRRSV-2 dominates, with extensive recombination and lineage change. New studies identify increasing emergence of NADC30-like, NADC34-like, and highly pathogenic recombinant virus, and recombination occurs most commonly with vaccine origin and field strains. Such heterogeneity complicates diagnosis, control, and vaccine development, the motive for continued molecular surveillance (Gao et al., 2017; Paploski et al., 2019; Yuan et al., 2025).
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