Fisheries and Ocean Canada, Nanaimo, BC, Canada.
J Fish Dis. 2021 Jan;44(1):1-9. doi: 10.1111/jfd.13261. Epub 2020 Oct 16.
Piscirickettsia salmonis, the aetiological agent of salmonid rickettsial septicaemia (SRS), is a global pathogen of wild and cultured marine salmonids. Here, we describe the development and application of a reproducible, standardized immersion challenge model to induce clinical SRS in juvenile pink (Oncorhynchus gorbuscha), Atlantic (Salmo salar) and sockeye salmon (O. nerka). Following a 1-hr immersion in 10 colony-forming units/ml, cumulative mortality in Atlantic salmon was 63.2% while mortality in sockeye salmon was 10%. Prevalence and levels of the bacterium in kidney prior to onset of mortality were lower in sockeye compared with Atlantic or pink salmon. The timing and magnitude of bacterial shedding were estimated from water samples collected during the exposure trials. Shedding was estimated to be 82-fold higher in Atlantic salmon as compared to sockeye salmon and peaked in the Atlantic salmon trial at 36 d post-immersion. These data suggest sockeye salmon are less susceptible to P. salmonis than Atlantic or pink salmon. Finally, skin lesions were observed on infected fish during all trials, often in the absence of detectable infection in kidney. As a result, we hypothesize that skin is the primary point of entry for P. salmonis during the immersion challenge.
鲑鱼鱼立克次体是导致鲑鱼立克次体败血症（SRS）的病原体，是野生和养殖海水鲑鱼的全球性病原体。在这里，我们描述了一种可重复、标准化的浸泡式挑战模型的开发和应用，该模型可诱导幼龄粉鲑（Oncorhynchus gorbuscha）、大西洋鲑（Salmo salar）和红鲑（O. nerka）发生临床 SRS。在 1 小时的 10 个菌落形成单位/ml 浸泡后，大西洋鲑鱼的累积死亡率为 63.2%，而红鲑鱼的死亡率为 10%。在死亡率发生之前，肾脏中细菌的流行率和水平在红鲑鱼中比大西洋鲑鱼或粉鲑鱼低。通过在暴露试验期间收集的水样来估计细菌的脱落时间和数量。与红鲑鱼相比，大西洋鲑鱼的脱落量估计要高 82 倍，在大西洋鲑鱼试验中，脱落量在浸泡后 36 天达到峰值。这些数据表明，与大西洋鲑鱼或粉鲑鱼相比，红鲑鱼对鲑鱼鱼立克次体的敏感性较低。最后，在所有试验中都观察到受感染鱼类出现皮肤损伤，而在肾脏中通常检测不到感染。因此，我们假设在浸泡式挑战期间，皮肤是鲑鱼鱼立克次体的主要入侵点。
