Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Camden, New South Wales, Australia.
School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Camden, New South Wales, Australia.
J Fish Dis. 2023 Jul;46(7):751-766. doi: 10.1111/jfd.13784. Epub 2023 Mar 26.
Most diseases in aquaculture are caused by opportunistic pathogens. One of them, Vibrio harveyi, is a widespread Gram-negative bacterium that has become an important pathogen of aquatic species in marine environments. Here, we propose the use of the causal pie model as a framework to conceptualize the causation of vibriosis in juvenile barramundi (Lates calcarifer) and to establish an effective challenge model. In the model, a sufficient cause, or the causal pie, is a constellation of component causes that lead to an outcome (e.g. vibriosis). In the pilot study, a high cumulative mortality (63.3% ± 10.0%, mean ± SE) was observed when V. harveyi was administered by intraperitoneal injection using a high challenge dose [10 colony-forming units (CFU) fish ], but low or no mortality was observed in fish subject to cold stress or fish with intact skin when challenged by immersion. We, therefore, tested the use of a skin lesion (induced with a 4-mm biopsy punch) combined with cold temperature stress to induce vibriosis following the causal pie model. After challenge, fish were immediately subject to cold stress (22°C) or placed at an optimal temperature of 30°C. All groups were challenged with 10 CFU mL for 60 min. A considerably higher mortality level (72.7% ± 13.9%) was observed in fish challenged with both a skin lesion and cold stress compared with mortality in fish only having a skin lesion (14.6% ± 2.8%). V. harveyi was re-isolated from all moribund fish and was detected by species-specific real-time PCR in gills, head kidney and liver, regardless of challenge treatment confirming vibriosis as the cause of disease. Parenchymal tissues had histopathological changes consistent with vibriosis. Whole-genome sequence (WGS) is provided for the Vibrio harveyi isolate examined in this study. Overall, the causal pie model was a useful framework to conceptualize the design of the experimental challenge model, in which both cold stress and skin damage were identified as component causes of vibriosis with high mortality. This conceptual framework can be applied to other opportunistic pathogens in aquaculture or to the study of co-infections in fish.
大多数水产养殖疾病是由机会性病原体引起的。其中，哈维氏弧菌是一种广泛存在的革兰氏阴性菌，已成为海洋环境中水生动物的重要病原体。在这里，我们提出使用因果饼图模型作为框架来概念化幼鱼（Lates calcarifer）弧菌病的病因，并建立有效的挑战模型。在该模型中，充分原因（或因果饼图）是导致结果（例如弧菌病）的一系列组成原因。在初步研究中，当以高挑战剂量[每尾 10 个集落形成单位（CFU）]通过腹腔注射施用哈维氏弧菌时，观察到 63.3%±10.0%（平均值±SE）的高累积死亡率，但在受到冷应激或皮肤完整的鱼中，观察到低死亡率或无死亡率。当受到浸泡挑战时。因此，我们根据因果饼图模型测试了使用皮肤损伤（用 4 毫米活检冲孔诱导）结合冷应激来诱导弧菌病的方法。挑战后，鱼立即受到冷应激（22°C）或置于最佳温度 30°C。所有组均用 10 个 CFU/mL 进行 60 分钟的挑战。与仅具有皮肤损伤的鱼类相比，同时具有皮肤损伤和冷应激的鱼类的死亡率（72.7%±13.9%）明显更高。从所有濒死鱼中重新分离出哈维氏弧菌，并通过种特异性实时 PCR 在鳃、头肾和肝脏中检测到，无论挑战处理如何，均证实弧菌病是疾病的原因。实质组织具有与弧菌病一致的组织病理学变化。提供了本研究中检查的哈维氏弧菌分离株的全基因组序列（WGS）。总体而言，因果饼图模型是一个有用的框架，可以将概念化实验挑战模型的设计，其中冷应激和皮肤损伤被确定为高死亡率弧菌病的组成原因。该概念框架可应用于水产养殖中的其他机会性病原体或鱼类的合并感染研究。
