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Research Document 2020/061

Characterization of Tenacibaculum maritimum and mouthrot to inform pathogen transfer risk assessments in British Columbia

By Wade, J. and Weber, L.


Mouthrot is a disease unique to salmonids of British Columbia (BC) and the United States (US) Pacific Northwest. Recently, the causative agent has been confirmed as Tenacibaculum maritimum in laboratory challenges with Norwegian Atlantic Salmon (Salmo salar) and isolates from farmed BC Atlantic Salmon exhibiting clinical signs of disease. Tenacibaculum maritimum is a gram-negative, filamentous bacterium which, in regions outside BC and the US Pacific Northwest, causes tenacibaculosis, an infection in many marine fish species globally. The clinical signs and gross pathology associated with strains of T. maritimum causing mouthrot and tenacibaculosis are different. Because of these differences and that mouthrot is found only in this region where the risk assessment is focused, it is important to separate out information pertaining to T. maritimum causing mouthrot and Tenacibaculum spp. causing tenacibaculosis.

Between 2002 and 2018 there were 106 farm-level mouthrot diagnoses made as a result of 1446 fish health audits conducted on Atlantic Salmon farms in BC. Mouthrot has been diagnosed every year since 2003 and from all Fish Health Surveillance Zones where audits were conducted. Although there was no requirement to report Fish Health Events (FHEs) between 2013 and 2015, from 2002 to 2013 and 2015 to 2018 there were 537 FHEs attributed to mouthrot reported on Atlantic Salmon farms in BC.

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