Pathology of experimentally induced mouthrot caused by Tenacibaculum maritimum in Atlantic salmon smolts

Abstract

Mouthrot, caused by Tenacibaculum maritimum is a significant disease of farmed Atlantic salmon, Salmo salar on the West Coast of North America. Smolts recently transferred into saltwater are the most susceptible and affected fish die with little internal or external clinical signs other than the characteristic small (usually < 5 mm) yellow plaques that are present inside the mouth. The mechanism by which these smolts die is unknown. This study investigated the microscopic pathology (histology and scanning electron microscopy) of bath infected smolts with Western Canadian T. maritimum isolates TmarCan15-1, TmarCan16-1 and TmarCan16-5 and compared the findings to what is seen in a natural outbreak of mouthrot. A real-time RT-PCR assay based on the outer membrane protein A specific for T. maritimum was designed and used to investigate the tissue tropism of the bacteria. The results from this showed that T. maritimum is detectable internally by real-time RT-PCR. This combined with the fact that the bacteria can be isolated from the kidney suggests that T. maritimum becomes systemic. The pathology in the infected smolts is primarily mouth lesions, including damaged tissues surrounding the teeth; the disease is similar to periodontal disease in mammals. The pathological changes are focal, severe, and occur very rapidly with little associated inflammation. Skin lesions are more common in experimentally infected smolts than in natural outbreaks, but this could be an artefact of the challenge dose, handling and tank used during the experiments.

Tenacibaculum piscium sp. nov., isolated from skin ulcers of sea-farmed fish, and description of Tenacibaculum finnmarkense sp. nov. with subdivision into genomovars finnmarkense and ulcerans

“…As the name 'T. finnmarkense' has already to some extent been adopted in scientific literature [10,14,[40][41][42][43], we therefore propose the name Tenacibaculum finnmarkense sp. nov. for this taxon with TNO006 T as the type strain.…”

Advancements in Characterizing Tenacibaculum Infections in Canada

“…F. psychrophilum is an etiological agent of bacterial cold-water disease (BCWD) and rainbow trout fry syndrome (RTFS) [ 37 , 38 ], while F. columnare is an etiological agent of columnaris disease [ 39 ]. Both T. maritimum [ 6 , 7 ] and T. finnmarkense [ 11 , 40 ] are thought to be etiological agents of tenacibaculosis in fishes. There are some similarities between columnaris disease [ 39 ] or BCWD/RTFS [ 37 , 38 ] with some clinical presentations of tenacibaculosis, where disease results in large ulcers on epidermal surfaces of fishes [ 6 , 7 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 40 ].…”

“…Two 16S rDNA PCR assays [ 80 , 81 ] are widely applied to identify T. maritimum [ 82 , 83 , 84 , 85 , 86 , 87 , 88 ]. qPCR and v-qPCR for 16S rDNA [ 89 , 90 , 91 ], gyrB gene [ 92 ], and outer membrane protein A (ompA) gene sequences [ 7 ] have been developed. The 16S rDNA assay [ 89 ] was determined to be more sensitive than the ompA gene assay [ 7 ].…”

“…Salmonid aquaculture started in Canada roughly 200 years ago, and as of 2017, Canada is now the fourth-largest supplier of salmonid products [ 1 , 2 , 3 ]. Recently, salmon farmers in British Columbia (BC; Canada) have experienced frequent mortality events in Atlantic salmon ( Salmo salar , AS) due to ‘mouthrot’ (a unique form of tenacibaculosis (other common names synonymous with mouthrot include yellow-mouth and bacterial stomatitis)) [ 4 , 5 , 6 , 7 , 8 ]. Mortality events in farmed fishes due to tenacibaculosis have also been experienced worldwide.…”

“…Mortality events in farmed fishes due to tenacibaculosis have also been experienced worldwide. Current research has shown that multiple species within the genus Tenacibaculum could be an etiological agent responsible for tenacibaculosis [ 6 , 7 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”