Viral infectious diseases pose a persistent challenge to global livestock production, animal welfare, and food security, emphasizing the critical role of early host defense mechanisms in limiting viral replication and transmission. As frontline sensors of infection, pattern recognition receptors (PRRs) detect viral nucleic acids and trigger antiviral innate immune responses via coordinated downstream signaling. This review summarizes the functions of three major PRR families, Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, emphasizing their involvement in detecting viral agents and activating downstream pathways, including NF-κB and IRF3/7. Particular attention is given to how these receptors function in pigs and poultry, highlighting their immune responses to economically significant viruses such as porcine reproductive and respiratory syndrome virus (PRRSV), African swine fever virus (ASFV), avian influenza virus (AIV), and Newcastle disease virus (NDV). The mechanisms by which PRRs activate interferon-mediated immune responses, as well as viral strategies to evade detection, are systematically discussed. Additionally, the review explores recent advances in understanding PRR signaling specificity across species, and their potential applications in vaccine adjuvant design or antiviral drug development are also reviewed. By integrating these insights, this work provides a theoretical foundation for improving disease prevention and control in livestock production.

Viral infection of professional phagocytes can compromise antibacterial immunity because the cellular machinery reshaped for viral replication and immune evasion overlaps with the machinery required for bacterial capture, intracellular killing, and inflammatory signaling. Phagocyte cell biology has defined core cytoskeletal and trafficking nodes, including Rho-family GTPase control of actin assembly, integrin-mediated adhesion, and Rab-dependent phagosome maturation, and shown how bacterial pathogens target these nodes to evade clearance. Here we ask how recently described porcine reproductive and respiratory syndrome virus (PRRSV) lesions in porcine alveolar macrophages (PAMs) fit into this established cell biology. Direct evidence supports reduced phagocytic capture and impaired intracellular bacterial killing in defined systems. In vivo coinfection studies also report worse outcomes. Enhanced association or internalization of selected bacteria has also been reported, with ITGα5 and filamin A upregulation proposed as a candidate explanation. PRRSV further disrupts innate-immune signaling, autophagy–lysosome trafficking, ER–mitochondrial metabolism, and lipid homeostasis. These changes may contribute to antibacterial failure, but bacterial endpoints were not measured in the same experiments. At the tissue level, macrophage attrition and altered bystander states may disrupt cytokine relay, creating a permissive lung environment even when only a minority of PAMs are productively infected. PRRSV is particularly informative because it productively infects a professional phagocyte in the natural host, allowing viral perturbation, macrophage antibacterial function, and bacterial challenge to be examined in one tractable system. Because the candidate nsp5–RhoA trafficking route and the ITGα5/FLNA entry route were reported in different experimental systems, their potential combination defines a testable hypothesis requiring co-validation in the same primary PAM system. We use the PRRSV–PAM axis as a natural-host model to examine how viral infection of professional phagocytes can produce macrophage antibacterial failure, with implications for virus-associated bacterial vulnerability in veterinary and human respiratory disease.