Combined immersion and oral vaccination of Vietnamese catfish (Pangasianodon hypophthalmus) confers protection against mortality caused by Edwardsiella ictaluri

Edwardsiella ictaluri septicemia occurs worldwide and causes high mortality and considerable economic damage to the catfish industry especially in Vietnam and the USA. To control Edwardsiella septicemia farmers extensively use antibiotics and various vaccination methods. Vaccination with inactivated vaccines has come with variable efficacy.In this trial the results of an approach of controlling Edwardsiella septicemia of Tra catfish (Pangasianodon hypophthalmus) in Vietnam through vaccination via mucosal surfaces are presented. The results show that a combination of primary vaccination by immersion with inactivated E. ictaluri followed by an oral boost with a formulated antigen preparation induces a statistically significant level of protection against mortality caused by experimental infection 4 weeks post-boost. Fish immunized by immersion only show significantly lower level of protection but significantly higher than the controls. Repeated boosts result in improved duration of immunity with a relative percent survival (RPS) of 47% at 90% control mortality. The immunization procedure provides an alternative for disease control through vaccination.