Aquaculture America 2024

February 18 - 21, 2024

San Antonio, Texas

EVALUATION OF ORAL ADJUVANTED KILLED Aeromonas hydrophila VACCINES IN CHANNEL CATFISH Ictalurus punctatus

Allison Wise*, Craig Shoemaker, Troy Bader, Benjamin Beck

USDA-ARS Aquatic Animal Health Research Unit

Auburn, AL 36832

allison.wise@usda.gov

 



 Virulent Aeromonas hydrophila (vAh ) attributes nearly $35 million dollars in economic losses within the southeastern catfish aquaculture industry. This bacterial pathogen infects channel and hybrid catfish inducing skin necrosis, internal and external hemorrhaging, and exophthalmia. Farmers can lose over 50% of a harvest yield in less than a week when infected, increasing the urgency for more effective preventative measures. Oral bacterin vaccination with the inclusion of an adjuvant is a promising solution providing ease of administration for farmers, while decreasing stress put onto the catfish. Bacterin vaccines typically mediate a high antibody response and even more so when boosted. Research has been conducted demonstrating adjuvant’s ability to also increase protection and duration of protection, thus this study’s first objective is to determine whether the addition of an adjuvant increases vaccine efficacy. Over the years, multiple strains of vAh have caused catastrophic mortalities in both Mississippi (S14-452) and Alabama (ALG-15-097). Due to the variation within vAh strains, objective two is to determine whether bacterin vaccines with adjuvants demonstrate cross-protection amongst S14-452 and ALG-15-097. Bacterin vaccines were made for S14-452 (1.10 x107) and ALG-15-097 (1.0 x107). To test objectives one and two, channel catfish (13 g) were separated into treatments (ALG-15-097, ALG-15-097 + adjuvant, S14-452, S14-452 + adjuvant, adjuvant only, sterile TSB). Feed was top-coated with each treatment and fed for 7 days at 2% body weight and boosted at 9 weeks. Fish were challenged at 3 and 12 weeks post-vaccination and boost. At 3 weeks, treatment groups were challenged with ALG-15-097 (3.4 × 10 7 CFU mL-1 ), and cumulative percent mortality was evaluated to determine efficacy and cross-protection. ALG-15-097 (49.3% ± 9.23) experienced significantly less mortality (P < 0.05 ) compared to adjuvant only (92% ± 6.93) and placebo groups (97.3% ± 2.31). At 12 weeks, treatment groups were challenged with ALG-15-097 and S14-457 . Post ALG-15-097 exposure, all vaccinated groups experienced significantly less mortality than adjuvanted groups (P < 0.05). No significant differences between vaccinated strains or adjuvanted vaccines were documented.  Post S14-457 exposure, ALG-15-097 (10.0% ± 10.0) experienced significantly less mortality (P < 0.05 ) compared to adjuvant only (56.6% ± 6.93) and placebo groups (73.3% ± 11.5). S14-457 vaccinated groups demonstrated protection (P < 0.05 ) as well compared to placebo groups.  Oral feed vaccines developed in this study demonstrated protection against vAh strains, while adjuvanted vaccines did not increase efficacy.  Results from this study allows for the development of more efficacious vaccine components and delivery on catfish farms, ultimately, preventing mass mortality due to vAh .