Effect of subcutaneous injection vaccine on protection against Cryptocaryon irritans infection

Abstract

Cryptocaryon irritans, an ectoparasitic protozoan, causes significant economic losses in marine fish farming. Vaccination is a crucial strategy for disease prevention, with injection being the most effective and widely used delivery method. Given that C. irritans primarily invades the skin, subcutaneous injection may better stimulate a localized immune response, providing faster and more efficient protection. In this study, orange-spotted groupers (Epinephelus coioides) were immunized with recombinant Tetrahymena thermophila tubulin protein via subcutaneous and intraperitoneal injection. The results showed that subcutaneous vaccination significantly enhanced immune protection, achieving a relative protection rate approximately 2.3 times higher than intraperitoneal vaccination. Specific IgM levels were consistently higher in the serum, mucus, and tissue culture medium of subcutaneously vaccinated fish, both before and after challenge. Notably, parasite-specific IgM levels were also elevated in this group. Immunofluorescence analysis revealed an increased number of IgM-positive cells in mucosal and systemic tissues. Histological analysis indicated that subcutaneously injected antigens were primarily retained in the skin and gradually degraded, whereas intraperitoneally injected antigens were captured in the spleen, highlighting differences in antigen distribution. These findings underscore the potential of subcutaneous injection as an effective vaccination route against C. irritans and provide valuable insights for optimizing immunization strategies in marine fish.