Since 2016, annually occurring species‐specific die‐offs of brown trout (Salmo trutta fario) occurred in the Thur River, situated in the Eastern part of Switzerland. These events lead to drastically reduced population densities in the impacted river regions. Clinical signs in brown trout and mortality were restricted to few weeks in August/September. To characterize the syndrome and to find possible causes, from end of March to November 2018, one‐year‐old brown trout (Salmo trutta fario) and rainbow trout (Oncorhynchus mykiss) were exposed to water from Thur River, fish were sampled regularly and screened for infectious agents, including viral metagenomics, and pathology was described. Starting approximately four months post‐exposure, brown trout showed severe lymphohistiocytic pancarditis and necrotizing and haemorrhagic hepatitis. These lesions were recorded until the end of the experiment in November. Rainbow trout were not affected at any point in time. No infectious agents could be identified so far as cause of disease, especially no viral aetiology. Even if pathogenesis and pathology point in the direction of an infectious agent, a causative relationship could not be confirmed and aetiology remains unclear.

中文翻译：

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导致瑞士东部野生褐鳟鱼高死亡率的神秘综合症，病理和寻找可能的原因。

自2016年以来，位于瑞士东部的瑟河（Thur River）每年发生特定物种的褐鳟（Salmo trutta fario）死亡。这些事件导致受影响河流地区的人口密度急剧下降。在八月/九月，褐鳟和死亡率的临床症状被限制在数周之内。为了表征该综合征并找出可能的原因，从2018年3月底至2018年11月，使用一岁的褐鳟（Salmo trutta fario）和虹鳟（Oncorhynchus mykiss）暴露于瑟河（Thur River）的水中，定期对鱼进行采样，并筛选包括病毒宏基因组学在内的传染原，并描述了病理学。暴露后约四个月开始，褐鳟鱼表现出严重的淋巴组织性全心炎和坏死性出血性肝炎。记录这些病变直到11月实验结束。虹鳟鱼在任何时候都不会受到影响。就疾病原因，尤其是没有病毒病因，无法确定任何传染原。即使发病机理和病理指向传染原，也不能确定病因，病因尚不清楚。