Chitosan nanoparticles as next-generation carriers for veterinary DNA vaccines: Mechanisms, immune responses, and translational prospects.

Chitosan-based DNA nanoparticles have emerged as a promising next-generation platform for veterinary vaccines, addressing several limitations of conventional attenuated, inactivated, and recombinant formulations. Chitosan is a biodegradable, biocompatible, and low toxicity polymer with mucoadhesive properties that enhance cellular uptake and protect nucleic acids from enzymatic degradation. These characteristics make it an attractive candidate for delivering plasmid DNA encoding viral antigens across diverse animal species. Recent advances demonstrate that chitosan-DNA nanoparticles can induce robust humoral and cellular immune responses, stimulate mucosal immunity, and achieve high levels of protection in terrestrial livestock, poultry, fish, and crustaceans. A wide range of viral pathogens has been targeted using this approach, including Foot-and-Mouth disease virus, Newcastle disease virus, infectious bronchitis virus, spring viremia of carp virus, white spot syndrome virus, and infectious pancreatic necrosis virus. Depending on the species and formulation strategy, nanoparticles have been successfully administered intranasally, intramuscularly, intraperitoneally, or orally, highlighting their versatility for mass vaccination in both terrestrial and aquatic systems. Reported protection rates range from 60% to 100% in mammalian and avian models, while oral nanoparticle vaccines in shrimp and fish have demonstrated sustained immune activation and survival benefits. The ability to incorporate genetic adjuvants, such as cytosine-phosphate-guanine motifs, cytokines, or complement fragments, further enhances the immunogenicity of these platforms. Despite these promising results, several challenges remain. Most studies use small laboratory animals or controlled experimental settings, and data from large-scale field trials in cattle, pigs, and equines remain scarce. The stability of nanoparticle formulations during long-term storage, the scalability of manufacturing processes, and the standardization of dosing regimens require further investigation. Overall, chitosan-DNA nanoparticles represent a safe, flexible, and rapidly adaptable vaccine carrier system with significant potential to transform veterinary immunization. Their capacity to elicit mucosal and systemic immunity, enable needle-free delivery, and support DIVA-compatible vaccine design positions them as a valuable tool for controlling emerging and re-emerging viral diseases in the context of One Health.