Abstract A strain of atypical Aeromonas hydrophila (aAh) has caused issues within the channel catfish Ictalurus punctatus industry of the southeastern United States since 2009. These atypical pathotypes cause acute mortality events resulting in catastrophic losses, as opposed to more chronic mortality and lesions seen in typical infections of motile aeromonas septicemia (MAS). This study provides a basic framework for rapid field sampling negating the need for re-isolation or enrichment culture, thereby reducing the time between sampling and detection. Rapid and accurate quantitative PCR based methods for detection of aAh have been described and are important confirmative tools in research and diagnostic settings. These methods also have application in epidemiological surveys investigating the spread of disease and elucidating pathogen dynamics that may lead to outbreaks. To date, no field-based sampling technique for rapid aAh detection in resident pond populations has been explored. In this study, culture swabs taken from the gills and lower intestine of pond-raised catfish were assessed for their suitability as rapid field-based collection methods for downstream applications. Results showed the state of the pond has a significant effect on which swab location yields the highest proportion of PCR positive results. During an active outbreak, gill swabs identified more fish as aAh-positive; however, in apparently healthy populations, swabs taken from the lower intestine identified significantly more aAh-positive fish than gill swabs, despite no statistical difference in the concentration of aAh cell equivalents between swab sites. Naive prevalence estimates from the two swab types were compared to estimates provided by a hierarchical occupancy model. Prevalence estimates from gill swabs was 0.95% while vent swabs showed a prevalence of 2.2%; however, estimates based on the occupancy model were 6.6% and 9.8%, respectively. This multi-fold increase in prevalence estimates highlights the importance of accounting for imperfect detection in epidemiological studies and in assessing potential outbreak risk. Furthermore, occupancy models based on these data indicate resident fish can be aAh-positive carriers with no gross signs of infection, providing evidence aAh can reside in catfish ponds in the absence of disease. The presence of a carrier state indicates the pathogen may pose minimal risk to the host is compromised or a mechanical portal of entry into the blood stream is available. This provides an important direction for future research in understanding the mechanisms of aAh outbreaks in catfish aquaculture ponds.

中文翻译：

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使用定量聚合酶链反应 (qPCR) 和占用模型来估计鲶鱼中非典型嗜水气单胞菌 (aAh) 的流行率

摘要 自 2009 年以来，一种非典型嗜水气单胞菌 (aAh) 菌株在美国东南部的鲶鱼 Ictalurus punctatus 产业中引起了问题。运动性气单胞菌败血症（MAS）的典型感染。这项研究为快速现场采样提供了一个基本框架，无需重新隔离或富集培养，从而减少了采样和检测之间的时间。已经描述了基于快速准确定量 PCR 的检测 aAh 的方法，并且是研究和诊断环境中的重要确认工具。这些方法也可用于调查疾病传播和阐明可能导致爆发的病原体动态的流行病学调查。迄今为止，尚未探索用于在常驻池塘种群中快速检测 aAh 的基于现场的采样技术。在这项研究中，评估了从池塘饲养的鲶鱼的鳃和下肠中取出的培养拭子作为下游应用的基于现场的快速收集方法的适用性。结果表明，池塘的状态对哪个拭子位置产生最高比例的 PCR 阳性结果有显着影响。在活跃爆发期间，鳃拭子鉴定出更多的鱼为 aAh 阳性；然而，在明显健康的人群中，从下肠采集的拭子比鳃拭子识别出更多的 aAh 阳性鱼，尽管拭子位点之间的 aAh 细胞当量浓度没有统计学差异。将两种拭子类型的朴素流行率估计值与分层占用模型提供的估计值进行比较。鳃拭子的流行率为 0.95%，而排气拭子的流行率为 2.2%；然而，基于入住率模型的估计分别为 6.6% 和 9.8%。流行率估计数的多倍增长凸显了在流行病学研究和评估潜在爆发风险中考虑不完善检测的重要性。此外，基于这些数据的占用模型表明，常驻鱼可能是 aAh 阳性携带者，没有明显的感染迹象，这提供了 aAh 可以在没有疾病的情况下留在鲶鱼池塘中的证据。携带者状态的存在表明病原体可能对宿主造成的风险最小，或者进入血流的机械入口是可用的。这为未来研究鲶鱼养殖池塘aAh爆发的机制提供了重要方向。