Vibrio harveyi, a recently discovered pathogenic bacterium isolated from American eels (Anguilla rostrata), poses uncertainties regarding its pathogenesis in American eel and the molecular mechanisms underlying host defense against V. harveyi infection. This study aimed to determine the LD₅₀ of V. harveyi in American eel and assess the bacterial load in the liver, spleen, and kidney post-infection with the LD50 dose. The results showed that the LD₅₀ of V. harveyi via intraperitoneal injection in American eels over a 14d period was determined to be 1.24 × 10³ cfu/g body weight (6.2 × 10⁴ cfu/fish). The peak bacterial load occurred at 36 h post-infection (hpi) in all three organs examined. Histopathology analysis revealed hepatic vein congestion and thrombi, tubular vacuolar degeneration, and splenic bleeding. Moreover, quantitative reverse transcription polymerase chain reaction (qRT-PCR) results indicated significant up or downregulation of 18 host immune- or anti-infection–related genes post 12 to 60 hpi following the infection. Additionally, RNA sequencing (RNA-seq) unveiled 7 hub differentially expressed genes (DEGs) and 11 encoded proteins play crucial roles in the anti-V. harveyi response in American eels. This study firstly represents the comprehensive report on the pathogenicity of V. harveyi to American eels and RNA-seq of host’s response to V. harveyi infection. These findings provide valuable insights into V. harveyi pathogenesis and the strategies employed by the host’s immune system at the transcriptomic level to combat V. harveyi infection.

哈维弧菌是最近从美洲鳗（ Anguilla rostrata ）中分离出来的一种致病菌，其在美洲鳗中的发病机制以及宿主防御哈维弧菌感染的分子机制尚不确定。本研究旨在确定美洲鳗中哈维弧菌的LD ₅₀，并用 LD50 剂量评估感染后肝脏、脾脏和肾脏中的细菌负荷。结果表明， 14天期间腹腔注射哈维氏弧菌对美洲鳗的LD ₅₀测定为1.24 × 10 ³  cfu/g体重（6.2 × 10 ⁴  cfu/鱼）。所有三个检查器官的细菌负荷峰值出现在感染后 36 小时 (hpi)。组织病理学分析显示肝静脉充血和血栓、管状空泡变性和脾出血。此外，定量逆转录聚合酶链反应 (qRT-PCR) 结果表明，感染后 12 至 60 hpi 后，18 个宿主免疫或抗感染相关基因显着上调或下调。此外，RNA 测序 (RNA-seq) 揭示了 7 个中心差异表达基因 (DEG) 和 11 个编码蛋白在美洲鳗的抗哈维弧菌反应中发挥着至关重要的作用。本研究首次全面报道了哈维弧菌对美洲鳗的致病性以及宿主对哈维弧菌感染反应的RNA-seq。这些发现为了解哈维氏弧菌发病机制以及宿主免疫系统在转录组水平上对抗哈维氏弧菌感染所采用的策略提供了有价值的见解。