Varying Flavobacterium psychrophilum shedding dynamics in three bacterial coldwater disease-susceptible salmonid (Family Salmonidae) species

• Published in: Microbiology Spectrum
• Main Authors: Christopher Knupp, Esteban Soto, Thomas P. Loch
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Society for Microbiology 2024
• Subjects: bacterial coldwater disease; rainbow trout fry syndrome; Flavobacterium; shedding; transmission; disease ecology; Microbiology; QR1-502; Atlantic salmon; Salmo salar
• Online Access: https://doi.org/10.1128/spectrum.03601-23; https://doaj.org/article/ed04a72a962c4e0da950cf496a318ebc

ABSTRACTFlavobacterium psychrophilum causes bacterial coldwater disease (BCWD) and is responsible for substantial losses in farm and hatchery-reared salmonids (Family Salmonidae). Although F. psychrophilum infects multiple economically important salmonids and is transmitted horizontally, the extent of knowledge regarding F. psychrophilum shedding rates and duration is limited to rainbow trout (Oncorhynchus mykiss). Concurrently, hundreds of F. psychrophilum sequence types (STs) have been described using multilocus sequence typing (MLST), and evidence suggests that some variants have distinct phenotypes, including differences in host associations. Whether shedding dynamics differ among F. psychrophilum variants and/or salmonids remains unknown. Thus, three F. psychrophilum isolates (e.g., US19, US62, and US87) in three MLST STs (e.g., ST13, ST277, and ST275) with apparent host associations for coho salmon (O. kisutch), Atlantic salmon (Salmo salar), or rainbow trout were intramuscularly injected into each respective fish species. Shedding rates of live and dead fish were determined by quantifying F. psychrophilum loads in water via quantitative PCR. Both live and dead Atlantic and coho salmon shed F. psychrophilum, as did live and dead rainbow trout. Regardless of salmonid species, dead fish shed F. psychrophilum at higher rates (e.g., up to ~108–1010 cells/fish/hour) compared to live fish (up to ~107–109 cells/fish/hour) and for a longer duration (5–35 days vs 98 days); however, shedding dynamics varied by F. psychrophilum variant and/or host species, a matter that may complicate BCWD management. Findings herein expand knowledge on F. psychrophilum shedding dynamics across multiple salmonid species and can be used to inform future BCWD management strategies.IMPORTANCEFlavobacterium psychrophilum causes bacterial coldwater disease (BCWD) and rainbow trout fry syndrome, both of which cause substantial losses in farmed and hatchery-reared salmon and trout populations worldwide. This study provides insight into F. ...