Semester of Graduation

Summer 2023

Degree

Master of Science (MS)

Department

Pathobiological Sciences

Document Type

Thesis

Abstract

Aquaculture is a globally important industry that faces significant challenges due to infectious diseases, which can result in substantial financial losses. In 2011, a new strain of Edwardsiella ictaluri emerged as a major pathogen affecting zebrafish in the ornamental fish industry, leading to high mortality rates and posing a severe threat to the sector. Vaccines provide potential benefits for disease prevention in aquaculture, particularly live-attenuated vaccines (LAVs), which induce strong host immune responses. Bacterial attenuation for vaccine development has evolved from serial passage to more targeted genetic modification techniques. However, regulatory constraints limit the availability of licensed LAVs for aquaculture. The rifampicin-supplemented serial passage technique has been widely used to attenuate pathogenic bacteria, resulting in successful live-attenuated bacterial vaccines for various fish pathogens, including E. ictaluri in catfish. Our study utilized this technique to develop a potential vaccine candidate against zebrafish edwardsiellosis, demonstrating complete attenuation of the zebrafish isolate LADL 11-194. Further investigation is needed to identify the specific genomic mutations responsible for the attenuation.

Three live-attenuated vaccine candidates, ΔesrC 11-100, ΔureG 11-100, and RREI 11-194, were tested for in their immunogenic potential in zebrafish against an E. ictaluri experimental challenge. Although E. ictaluri-related virulence factors have shown promise as vaccine candidates against enteric septicemia of catfish, our study found that none of the three tested attenuated isolates provided increased protection against edwardsiellosis in zebrafish. Environmental temperature and body condition did not significantly affect zebrafish mortality when exposed to a virulent E. ictaluri isolate. The persistence of E. ictaluri in recirculating tank systems raises concerns about potential re-exposure of surviving individuals. Genetic comparisons suggest that targeting the type 4 secretory pathway may offer improved protection. Understanding the genetic differences between E. ictaluri isolates of different host origins is crucial for disease management in aquaculture. There is a strong demand for a zebrafish edwardsiellosis vaccine, highlighting the need for further research and development to ensure proper protection in zebrafish aquaculture facilities.

Date

7-12-2023

Committee Chair

Hawke, John P.

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