Aquaculture America 2024

February 18 - 21, 2024

San Antonio, Texas

VIRULENCE OF NOVEL FLAVOBACTERIACEAE ISOLATES FROM THE WESTERN UNITED STATES AND ASSESSMENT OF POTENTIAL CROSS-PROTECTION OF AN ATTENUATED BCWD VACCINE

Brent M. Vuglar*, Jie Ma, Taylor I. Heckman, Esteban Soto, and Kenneth D. Cain

 

Department of Fish and Wildlife Sciences

College of Natural Resources

University of Idaho

  875 Perimeter Dr. MS 1136

Moscow, ID, USA, 83844

 vugl2592@vandals.uidaho.edu

 



In salmonid production, the most common pathogenic threats to fish stocks arise from members of the family Flavobacteriaceae, most notably: Flavobacterium psychrophilum,  F. branchiophilum, and F. columnare.  Clinical cases of disease caused by  new and emerging  bacterial strains in this family (Flavobacteriaceae) have been increasing.  In this study, a n assessment  of virulence was conducted on four  novel Flavobacteri um spp. isolated from clinical disease cases  from hatcheries in  the Western  region of the United States: 11299 (WA), 3gHT (UT), CA143 (CA), and CO45A (CO).  Juvenile rainbow trout, O. mykiss ,  were challenged  with  the isolates mentioned above.  Each isolate was  administered  via  intramuscular injection  at a dose of 10 7 CFUfish-1 . Results showed that these four Flavobacteriaceae  isolates were highly virulent and caused acute clinical disease. Cumulative percent mortality (CPM)  for isolates 11299, 3gHT, CA143 , and CO45A  was 46.7%, 93. 3%, 96.7%, and 96.7%, respectively .  Following virulence analysis, an investigation of cross-protection against these four isolates was initiated. A live-attenuated  F. psychrophilum  vaccine, previously developed and demonstrated to provide protection against an array of F.  psychrophilum  strains as well as mixed groups of Chryseobacterium spp. and Flavobacterium spp., was utilized.  Juvenile rainbow trout (Oncorhynchus mykiss) were vaccinated by immersion and high serum anti-F. psychrophilum antibody  titers developed. Fish were then challenged with isolates 11299, 3gHT, CA143, CO45A, and a mixed combination. Cross-protection to isolate  11299  was demonstrated with a  relative percent survival (RPS) of 36.21% compared to the unvaccinated 1 1299 control group (p<  0.05). Cross-protection was also observed  in groups challenged with the  mixture of the four isolates with an RPS of 41.46% (p<0.05). However, no protection was  observed in  groups challenged with the 3gHT, CA143, and CO45A isolates alone. Results from this s tudy confirm that these emerging flavobacterial strains cause clinical disease and suggest that an attenuated  F. psychrophilum vaccine may provide some benefit through cross-protective immunity.