In ovo methods for utilizing the modified live Edwardsiella ictaluri vaccine against enteric septicemia in channel catfish

Eyed channel catfish (Ictalurus punctatus) eggs were vaccinated by immersion exposure (10 min) with either the modified live Edwardsiella ictaluri isolate RE-33 grown in brain heart infusion broth (trial 1) or the lyophilized AQUAVAC-ESC(TM) vaccine (trial 2). AQUAVAC-ESC(TM) is the modified live E. ictaluri isolate (RE-33) that was licensed, produced and marketed as a vaccine against enteric septicemia of catfish by Intervet. Trial 1 consisted of vaccinated (RE-33 E. ictaluri at 1 X 10(5) CFU/ml) and non-vaccinated (controls) treatments with the eyed eggs hatching into fry 4 days following treatment. No mortality was recorded in these fish for 33 days post vaccination. In trial 2, three treatments were used: single vaccinated, vaccinated and fry booster vaccinated 7 days following initial immunization; and non-vaccinated (controls). The vaccination in trial 2 was carried out according to the manufacturer's recommendation for use on channel catfish fry (i.e. AQUAVAC-ESC(TM) label). In trial 2, the eyed eggs hatched 24 h post vaccination and no control fish or single-vaccinated fish died following vaccination. Three fry died in the booster vaccinated treatment. No rifampicin-resistant E. ictaluri was isolated from these dead Fish. Thirty-three (trial 1) and sixty days (trial 2) following vaccination, fish were challenged with E. ictaluri (isolate AL-93-75) at I X 10(7) CFU/mL in trial 1, the relative percentage survival (RPS) of vaccinates was 87.9; however, data did not fit Amend's criteria of 60% mortality in the non-vaccinated treatment and no significant difference was seen between mortality of the vaccinates or control treatments in trial I [Dev. Biol. Stand. 49 (1981) 447]. In trial 2, mean percentage mortality in the non-vaccinated treatment (controls) (64.2 +/- 5.8) was significantly higher ( p = 0.003) than mean percentage mortality in the single vaccinated treatment and booster vaccinated treatment (25.8 +/- 5.1 and 46.7 +/- 0.8, respectively). Relative percentage survival was 59.7 in the single vaccinated treatment and 27.3 in the booster vaccinates. Safety and efficacy of the modified live E. ictaluri vaccine (AQUAVAC-ESC(TM)) was demonstrated in eyed channel catfish eggs following single vaccination. Booster vaccination did not enhance vaccine efficacy; however, timing of the booster may have been too soon following initial vaccination of eyed eggs. Published by Elsevier Science B.V.