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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #314367
Title: Weissellosis: An Emerging Disease Of Farmed Rainbow Trout

Author
item Welch, Timothy - Tim
item HINSHAW, JEFFREY - North Carolina State University
item MITCHELL, HUGH - Aqua Tactics Fish Health & Vaccines
item GOOD, CHRISTOPHER - Freshwater Institute
item Marancik, David

Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 3/2/2015
Publication Date: 3/2/2015
Citation: Welch, T.J., Hinshaw, J.M., Mitchell, H., Good, C.M., Marancik, D.P. 2015. Weissellosis: An Emerging Disease Of Farmed Rainbow Trout. Annual Eastern Fish Health Workshop. Paper No. 30A.

Interpretive Summary:

Technical Abstract: Weissella ceti is a gram positive bacterium associated with Weissellosis, an emerging disease of farmed rainbow trout. This disease can result in high mortality in large fish (0.5-1.0 kg) and hence can cause significant economic loss. In the summer of 2011, severe Weissellosis outbreaks were identified at two commercial trout farms in North Carolina. The outbreaks subsided as water temperatures cooled in November; however, in the spring of 2012 the outbreaks recommenced thus demonstrating that this pathogen has the potential to persist in North Carolina through the winter months and suggesting that W. ceti could become an endemic disease problem in this area. Laboratory-based vaccination-challenge studies demonstrated that an aqueous vaccine formulation containing formalin-inactivated W. ceti whole-cells conferred significant protection against experimental infection, suggesting that vaccination could be a viable means of controlling this pathogen. In 2012, all fish at the two affected farms were vaccinated using a custom bacterin vaccine produced and prescribed by a licensed veterinarian, with the exception of 10,000 fish that were left unvaccinated to serve as controls to aid in evaluation of vaccine performance. Challenge experiments performed approximately one year post-vaccination demonstrated that on farm vaccinated fish displayed significant protection when compared to unvaccinated controls (RPS = 65%). More importantly, after comprehensive vaccination was initiated in 2012 no cases of Weissellosis were detected on either of the farms impacted by the outbreak although the pathogen was detected at a nearby farm that had not used the vaccine. Additional surveillance performed in the summers of 2013 and 2014 on the 15 remaining farms in the county and in the counties contiguous to the original outbreak sites has also been negative.