Almost eliminates this deformity
A study identifies so-called foetal bovine serum in vaccines as an important risk factor for spinal deformities in farmed salmon.
This is revealed in a research article recently published in the Journal of Fish Diseases. It shows a strong correlation between foetal bovine serum residues in oil-adjuvanted vaccines (OAVs) and the occurrence of "cross-stitch" changes in the vertebrae – a condition associated with significantly reduced growth.
Foetal bovine serum (FBS) may appear in fish vaccines as a residue from cell culture in some vaccine production processes.
Cross-stitch changes in the vertebrae (CSV) are a specific spinal pathology that is associated with reduced growth and impaired welfare in farmed Atlantic salmon.
A press release from MSD Animal Health claims that the findings provide important new insight into a condition of great importance to the aquaculture industry.
“This research is an important step forward in understanding vaccine-related adverse events in salmon. By identifying the specific role that FBS plays, we can further develop vaccine production to enhance fish welfare, improve production outcomes, and offer our customers safer and more effective solutions for fish health,” said Stephanie Steeves, global head of aqua at MSD Animal Health.
The study
The study investigated the effect of five different OAV formulations, with and without inactivated salmonid alphavirus (SAV) antigen and/or FBS, in Atlantic salmon. Previous observations in the industry had linked these deformities to some SAV vaccines, but this study was designed to isolate which component was the cause.
Among the important findings from the study, MSD highlights the following:
High incidence of deformities with FBS: Fish vaccinated with FBS had a significantly higher incidence of cross-stitch changes in the vertebrae (up to 51.7%) and visible dorsal changes (up to 39.2%).
In comparison, fish vaccinated with FBS-free vaccines, including vaccines with SAV antigen, had an incidence of cross-stitch changes of between 0 and 1.0%.
Significantly reduced growth: The study demonstrated a direct correlation between the severity of cross-stitch changes and reduced growth. Fish with 10 or more consecutive affected vertebrae had significantly lower harvest weight.
Economic consequences and importance for fish welfare: The findings confirm that cross-stitch vertebrae pathology impairs growth, which can lead to economic losses and reduced fish welfare.
“This study provides the aquaculture industry with a clear, data-based explanation for a costly and challenging fish health problem,” says Ragnar Thorarinsson, lead author of the study and senior researcher at MSD Animal Health.
“Our findings clearly show that removing FBS from the vaccine formulation virtually eliminates the risk of these specific deformities. This allows for the development of improved vaccines that protect against important viral diseases such as pancreas disease, when inactivated whole virus components are used, without compromising spinal health or growth.”
MSD Animal Health has recently launched a new seven-component, serum-free vaccine, available in Norway and the UK.
“While traditional viral vaccines use foetal bovine serum (FBS) during cell culture in production, AQUAVAC S7 is developed completely without serum components,” MSD says.
About the study design
The study was conducted under controlled experimental conditions, where Atlantic salmon were allocated to different smoltification and temperature regimes to mimic real production cycles.
The fish were vaccinated with one of five multivalent OAV formulations and followed for approximately 10 months in sea cages.
At the end of the study, the researchers conducted comprehensive assessments of vaccine-induced adverse events, spinal deformities using X-ray examinations, and growth.