Viruses and Antiviral Responses of Nematodes.

Nematodes are ubiquitous metazoans that occupy diverse ecological niches, exposing them to a wide range of viruses and positioning them as both viral hosts and vectors. Free-living nematodes, particularly Caenorhabditis elegans and Caenorhabditis briggsae, provide powerful genetic models for studying antiviral immune mechanisms. Natural infections with noda-like viruses have revealed powerful antiviral defense strategies in Caenorhabditis species, including RNA interference, the Intracellular Pathogen Response, Signal Transducers and Activators of Transcription (STAT)-like transcriptional regulation, terminal RNA uridylation, and structural barriers to viral entry and egress. These mechanisms demonstrate robust antiviral mechanisms independent of canonical interferon signaling while relying on conserved principles of viral RNA recognition, signal amplification, and coordinated transcriptional responses. Beyond free-living species, parasitic nematodes harbor a diverse and largely unexplored virome. Plant-parasitic nematodes host multiple RNA viruses and act as vectors for economically and agriculturally important plant pathogens, while animal-parasitic nematodes carry persistent viral infections that may influence the immune responses and disease outcomes of their animal hosts. Evidence for functional antiviral RNA interference in parasitic nematodes suggests partial conservation of immune mechanisms, although functional data remain limited. Together, these findings define current knowledge of viral infections and antiviral responses in nematodes and emphasize the need for deeper mechanistic studies, particularly in parasitic species, where the molecular basis of viral recognition and immune defense remains poorly characterized.