Evaluation of the protective effects of DNA vaccines encoding an infection-related cysteine protease from Cryptocaryon irritans, the pathogenic organism of cryptocaryoniasis

Abstract

Cryptocaryoniasis, caused by Cryptocaryon irritans, is a major threat to marine cage culture in tropical and subtropical waters; however, controlling the disease remains challenging. In this study, we constructed DNA vaccines encoding a cysteine protease of C. irritans (pcDNA3.1-cp2-full-myc and pcDNA3.1-cp2-partial-myc) and examined the protective efficacy of the vaccines. The results of the challenge experiment showed that the number of parasites recovered from fish immunized with the DNA vaccines was lower than that recovered from control fish (phosphate-buffered saline-injected and mock vector-injected groups); this difference was statistically significant when pcDNA3.1-cp2-full-myc was used for vaccination (p < 0.05). In addition, the cysteine protease was found to be relatively conserved among different isolates of the parasite. Thus, the protease may be a potential antigen candidate for the development of a vaccine against multiple strains of C. irritans.