Immune Responses to Myxozoan Parasites in Fish Systems

Myxozoan parasites, a diverse clade within the Cnidaria, exploit complex lifecycles that alternate between invertebrate and fish hosts, often establishing covert or chronic infections. In fish, the first line of defence comprises innate immune effectors such as macrophages, neutrophils and pattern‐recognition receptors that detect conserved parasite molecules. Successful containment may involve the formation of granulomatous cysts or encapsulation structures that limit parasite proliferation. If local barriers fail, adaptive immunity becomes crucial: B lymphocytes produce specific immunoglobulins, chiefly IgM, to neutralise spores and merozoites, while T lymphocytes orchestrate cellular responses through cytokines such as interferon-γ, promoting macrophage activation. Many myxozoans, however, deploy immune‐evasion strategies, including downregulation of host cytokines or induction of regulatory pathways, creating an immunosuppressed niche. This dynamic interplay shapes disease outcome, ranging from benign carriage to severe enteritis or gill pathology, with high mortality in aquaculture settings. Recent advances in transcriptomic and proteomic profiling have illuminated host–parasite dialogues, revealing biomarkers of resistance and potential targets for immunomodulation. A deeper understanding of these responses underpins the development of vaccines, selective breeding and dietary immunostimulants aimed at reducing economic losses and safeguarding wild fish populations.

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Immune Responses to Myxozoan Parasites in Fish Systems publication trend

The graph below shows the total number of articles in immune responses to myxozoan parasites in fish systems across all publications each year (not limited to Nature Index journals).

Technical terms

Granuloma: A structured aggregate of immune cells formed to contain persistent pathogens by physical encapsulation.

Interferon-γ (IFN-γ): A cytokine produced by T lymphocytes and natural killer cells that enhances antigen presentation and macrophage microbicidal functions.

Transcriptomics: The large-scale study of RNA transcripts produced by an organism’s genome under specific conditions, revealing gene expression changes.

Apoptosis: Programmed cell death characterised by DNA fragmentation and membrane blebbing, often exploited by pathogens to subvert host defences.

Immunosuppression: The reduction or inhibition of immune system components, which can be induced by parasites to facilitate infection.

References

1. To React or Not to React: The Dilemma of Fish Immune Systems Facing Myxozoan Infections. Frontiers in Immunology (2021).
2. Infection by the Parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) Suppresses the Immune System of Hybrid Tilapia. Microorganisms (2022).
3. Immunosuppression and apoptosis activation mediated by p53-Bcl2/Bax signaling pathway -The potential mechanism of goldfish (Carassius auratus Linnaeus) gill disease caused by Myxobolus ampullicapsulatus. Frontiers in Immunology (2022).
4. A tale of two fish: Comparative transcriptomics of resistant and susceptible steelhead following exposure to Ceratonova shasta highlights differences in parasite recognition. PLOS ONE (2021).