Aquaculture America 2020

February 9 - 12, 2020

Honolulu, Hawaii

CROSS-PROTECTION OF A LIVE-ATTENUATED COLDWATER DISEASE IMMERSION VACCINE AGAINST NOVEL FLAVOBACTERIUM spp. AND CHRYSEOBACTERIUM spp.

 
Timothy J. Bruce *, Jie Ma, Christopher Knupp , Thomas P. Loch,  and  Kenneth  D. Cain
 
Department of Fish and Wildlife Science s
875 Perimeter Dr. MS1136
University of Idaho
Moscow, ID, 83844-1136
tbruce@uidaho.edu
 

Flavobacterium spp. infections remain a major aquaculture industry issue and can cause major losses to fish stocks and economic implications.  For salmonid producers, a common threat within this genus is F. psychrophilum , the causative agent of bacterial coldwater disease (BCWD). Recent advancements in BCWD disease management have included a live-attenuated vaccine that provides cross-protection from an array of F. psychrophilum  strains. Emerging  family Flavobacteriaceae isolates have also been identified in global fish health diagnostic cases and include novel, virulent Flavobacterium spp., and Chryseobacterium species. The cross-protective ability of this live-attenuated F. psychrophilum vaccine against novel Flavobacteriaceae was evaluated in juvenile rainbow trout. Fish developed high F. psychrophilum -specific  antibody titers 8 weeks post-vaccination, with the vaccinated fish showing a greater response than mock-vaccinates (P<0.001) as expected. Fish were  then challenged with two  Chryseobacterium  spp. (S25 and T28), a Flavobacterium spp. (S21), a mixed combination of S21:S25:T28 strains , and a standard virulent  F. psychrophilum CSF259-93 strain . With respect to vaccination, the 259-93 V group  had a relative percent survival (RPS) of  94.44% compared to the control (259-93 C) fish (P<0.001) . Interestingly, vaccinated fish also had a high RPS (85.18%) following the  mixed Flavobacteriaceae infection.  Protection was not  observed  following challenge with the  single novel Flavobacteriaceae strains. Analysis of whole-cell lysates  of bacterial strains revealed differences in protein profiles (SDS-PAGE), but antigenic regions were observed in S25 and T28 when probed with post-challenge sera from surviving fish the mixed S21:S25:T28 and CSF259-93 groups in a western blot . Results indicate that the live-attenuated  F. psychrophilum  vaccine provides indirect protection against mixed infections with novel Flavobacteriaceae, but  further work  is needed  to determine the  synergistic virulence mechanisms for these emerging isolates.