Long-term Persistent Infection with Edwardsiella anguillarum Induces Protective Host Immunity in Red Seabream Pagrus major

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Edwardsiellosis in red seabream caused by Edwardsiella anguillarum results in economic losses. Fish were experimentally infected under natural temperature conditions (21.4–27.3°C), reaching a cumulative mortality of 26.5% at 134 days. Survivors retained the bacterium for >100 days, with re-isolation rates of 60–90%, suggesting long-term persistence and their potential role as reservoirs in aquaculture systems. Four reinfection trials were conducted at 28°C between days 29 and 134 post initial experimental infection. In all trials except one, survival was significantly higher in persistently infected fish than in naïve fish, suggesting resistance to reinfection.