Nocardiosis Pathogenesis in Aquaculture Systems

Nocardiosis in aquaculture is caused primarily by Nocardia seriolae, a filamentous Gram-positive bacterium that thrives in both marine and freshwater environments. Infection typically occurs through breaches in the skin or gill epithelium, allowing bacteria to invade and be phagocytosed by macrophages. Within these cells, Nocardia can manipulate apoptotic pathways and reactive oxygen species production to establish intracellular persistence. The ensuing immune response features the formation of granulomas—organized aggregates of macrophages, epithelioid cells and fibroblasts—that serve both to contain and, paradoxically, to sustain chronic infection. Environmental stressors such as high stocking densities, suboptimal water quality and temperature fluctuations exacerbate disease severity and facilitate transmission. Genomic and transcriptomic investigations have begun to identify virulence determinants, including metal-acquisition systems and secreted enzymes, as well as host genes involved in cytokine signalling and antimicrobial peptide production. Control strategies encompass enhanced biosecurity, targeted use of antimicrobials, vaccine development and emerging non-antibiotic approaches such as immunostimulants and probiotics. Given the global scale of finfish and shellfish farming, a deeper understanding of host–pathogen dynamics is crucial for designing integrated management practices that mitigate economic losses and curb the emergence of antimicrobial resistance.

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Nocardiosis Pathogenesis in Aquaculture Systems publication trend

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Technical terms

Granuloma: A structured aggregate of immune cells formed in response to persistent pathogens or foreign material.

Macrophage: A phagocytic innate immune cell that engulfs pathogens and orchestrates inflammatory responses.

Cytokine: A signalling protein secreted by immune cells to coordinate host-defence mechanisms.

Interferon-gamma (IFN-γ): A cytokine critical for activating macrophages and enhancing microbial clearance.

Probiotics: Live microorganisms that, when administered in adequate amounts, confer a health benefit to the host.

References

1. IFN-γ enhances protective efficacy against Nocardia seriolae infection in largemouth bass (Micropterus salmoides). Frontiers in Immunology (2024).
2. Intracellular behavior of Nocardia seriolae and its apoptotic effect on RAW264.7 macrophages. Frontiers in Cellular and Infection Microbiology (2023).
3. Single-strain probiotics enhance growth, anti-pathogen immunity, and resistance to Nocardia seriolae in grey mullet (Mugil cephalus) via gut microbiota modulation. Animal Microbiome (2024).
4. Analysis of the complete genome sequence of Nocardia seriolae UTF1, the causative agent of fish nocardiosis: The first reference genome sequence of the fish pathogenic Nocardia species. PLOS ONE (2017).
5. Transcriptome analysis in the spleen of Northern Snakehead (Channa argus) challenged with Nocardia seriolae. Genomics (2022).