| dc.description.abstract | Mouthrot is a serious disease affecting recently sea launched Atlantic salmon (Salmo salar) smolt in British Columbia (Canada) and has been a well-known concern for decades. Still, it was just recently that Tenacibaculum maritimum was proven to be the causative agent for this disease. Mouthrot causes welfare concerns, mortalities, and economic losses. There are currently no commercially available vaccines against mouthrot in Atlantic salmon, resulting in the need for antibiotics to manage outbreaks. Finding a sustainable way to prevent the disease is therefore important.
This current study is part of a larger project on vaccine development against mouthrot. In this study, two novel vaccines were tested to evaluate their efficacies in protecting Atlantic salmon smolts against mouthrot. The intraperitoneally administered recombinant sub-unit vaccines with aqueous adjuvants had been selected based on previous studies showing promising results. A Canadian T. maritimum isolate designated TmarCAN 15-1 was used to replicate the disease following vaccination and immunization. The fish were divided into three treatment groups: One was a naïve control group, and the others were vaccine groups vaccinated with Test vaccine 1 or Test vaccine 2. Additionally, a group of untreated fish were used as shedders in cohabitation challenge. Two challenge models were conducted in this current study. One half of the fish in each treatment group was challenged through immersion and the other half challenged through a cohabitation challenge. In the latter, the treatment groups were cohabitated with immersion challenged naïve shedder fish. Both models successfully reproduced mouthrot, but it was observed higher stress on the gills of fish challenged through immersion. This may have triggered an acceleration in mortalities deviating from the normal disease progression. The cohabitation challenged fish appeared to replicate a more representative mode of transmission and accurate clinical picture.
Mortalities were high in all groups. In both challenges the probability of survival was higher in the control group than the group vaccinated with Test vaccine 1. Also in both challenges, the group vaccinated with Test vaccine 2 showed a higher probability of survival compared to the control group, but the increased survival was shown to be non-significant. As this study demonstrated a lack of protection against mouthrot using these vaccines, further research should investigate other vaccine types or modes of administration, as well as other preventative measures against mouthrot. | |