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

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 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.由海栖屈挠杆菌（Tenacibaculum maritimum）引发的烂嘴病，是北美西海岸养殖大西洋鲑（Salmo salar）的重要病害。刚被转移至海水环境中的稚鲑最易感染该病，染病个体几乎无明显内外临床症状便会死亡，仅出现特征性小型病灶。本研究选取海栖屈挠杆菌菌株TmarCan15-1、TmarCan16-1及TmarCan16-5开展实验，并将实验结果与自然爆发的烂嘴病临床表征进行对比。 研究团队设计并采用基于海栖屈挠杆菌特异性外膜蛋白A（outer membrane protein A）的实时逆转录聚合酶链反应（real-time RT-PCR）检测方法，探究该菌的组织嗜性。检测结果显示，可通过实时RT-PCR在宿主体内检出海栖屈挠杆菌；结合可从肾脏分离得到该菌的事实，提示该菌可引发全身性感染。 受感染稚鲑的病理变化主要表现为口腔病变，包括牙齿周围软组织损伤；该病害与哺乳动物的牙周病表现相似。其病理特征为局灶性、重度损伤，且病程进展迅速，几乎不伴随炎症反应。实验感染稚鲑的皮肤病灶发生率高于自然爆发病例，但该差异可能是实验中攻毒剂量、操作方式及养殖水族箱差异导致的实验假象。