“Live vaccine is a promising vaccine against nocardiosis in Japanese amberjack Seriola quinqueradiata (6984)”

Live vaccine is a promising vaccine against nocardiosis in Japanese amberjack Seriola quinqueradiata

Introduction: Nocardiosis, a lethal granulomatous disease caused by aerobic actinomyces Nocardia spp., has been reported worldwide in many fish species. Mass mortality events of Seriola species including Japanese amberjack S. quinqueradiata infected with N. seriolae have caused significant economic losses in Japan, accounting for more than 40% of total yearly losses in these species. A promising vaccine against nocardiosis has yet to be developed for Japanese amberjack, a species that is more susceptible to the disease than other fish.

Methodology: We performed vaccine trials using inactivated, DNA, and live vaccine preparations to develop a promising vaccine that can control the nocardiosis occurrence in Japanese amberjack, the most commonly produced fish species in Japan. A low-virulent and suitable live vaccine strain was screened from several N. seriolae isolates derived from infected Seriola species. To measure cell-mediated immune responses against these vaccines, interferon-gamma (IFNγ) protein production by leukocytes was analyzed by the Interferon Gamma Release Assay.

Results: A live vaccine using a low-virulence isolate of N. seriolae conferred significant protection against the disease (relative percent survival (RPS) = 85.7%). No lesions typical of nocardiosis were observed in fish vaccinated with the isolate. Neither inactivated vaccines using formalin-killed cells, ultraviolet-treated bacteria nor DNA vaccine encoding the Ag85 gene of that promising results have been reported in related species greater amberjack S. dumerili did not promote significant protection. An approximately 1-year trial demonstrated the long-term effectiveness of the live vaccine. The live vaccine significantly enhanced the production of IFNγ, a key regulator of cell-mediated immune responses to eliminate the intracellular pathogen by leukocytes, whereas the other vaccines did not promote IFNγ production.

Conclusion: This study demonstrated a live vaccine that induces strong, long-term efficacy in protecting against nocardiosis caused by N. seriolae in Japanese amberjack. Unlike other vaccines, the live vaccine significantly promoted IFNγ production by leukocytes, indicating that cell-mediated immunity against N. seriolae confers protection against the disease. These results suggest that the live vaccine we developed is a promising vaccine for controlling nocardiosis in Japanese amberjack and could therefore reduce the significant economic losses attributed to this disease. We are now evaluating the risk of reversion to virulence and long-term latency of the vaccine strain to address the safety concerns related to live vaccines.

1. MATSUURA, YUTA, JAPAN FISHERIES RESEARCH AND EDUCATION AGENCY, Presenter
2. TAKANO, Tomokazu, JAPAN FISHERIES RESEARCH AND EDUCATION AGENCY, Author
3. SHIMAHARA, Yoshiko, JAPAN FISHERIES RESEARCH AND EDUCATION AGENCY, Author
4. YOSHINO, Tomoaki, JAPAN FISHERIES RESEARCH AND EDUCATION AGENCY, Author
5. SAKAI, Takamitsu, JAPAN FISHERIES RESEARCH AND EDUCATION AGENCY, Author
6. MATSUYAMA, Tomomasa, JAPAN FISHERIES RESEARCH AND EDUCATION AGENCY, Author