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

Abstract

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.