Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California, USA.
Aquatic Animal Diseases Laboratory, Aquaculture Department, National Institute of Oceanography and Fisheries, Suez, Egypt.
Transbound Emerg Dis. 2022 Jul;69(4):2326-2343. doi: 10.1111/tbed.14250. Epub 2021 Aug 25.
Lactococcus garvieae is an emergent bacterial pathogen of salmonid fish in North America that causes acute infections particularly at water temperatures above 15°C. During 2020, L. garvieae was detected in rainbow trout, Onchorhyncus mykiss, cultured in Southern California and the Eastern Sierras. Infected fish exhibited high mortalities and nonspecific clinical signs of lethargy, erratic swimming, dark skin pigmentation, and exophthalmia. Macroscopic changes included external and internal hemorrhages, mainly in the eyes, liver, coelomic fat, intestine, and brain. Histological examination revealed splenitis, branchitis, panophthalmitis, hepatitis, enteritis, and coelomitis, with variable degrees of tissue damage among evaluated fish. Pure colonies of L. garvieae were isolated from infected trout and specific PCR primers for L. garvieae confirmed the preliminary diagnosis. Multilocus sequence analysis showed that the strains recovered from diseased trout represent a novel genetic group. Isolates were able to form biofilms within 24 h that increased their resistance to disinfection by hydrogen peroxide. Laboratory challenge methods for inducing lactococcosis in steelhead trout, O. mykiss, were evaluated by intracoelomic injection with serial dilutions of L. garvieae. The median lethal dose 21 days post challenge was ∼20 colony-forming units/fish. Experimentally infected trout presented similar clinical signs, gross changes, and microscopic lesions as those with natural disease, fulfilling Koch's postulates and demonstrating the high virulence of the recovered strains.
海鱼利斯特氏菌是一种新兴的北美鲑鱼细菌性病原体，尤其在水温高于 15°C 时会引起急性感染。2020 年，在加利福尼亚南部和东内华达养殖的虹鳟鱼中检测到海鱼利斯特氏菌。患病鱼表现出高死亡率和昏睡、游动异常、皮肤色素沉着和眼球突出等非特异性临床症状。宏观变化包括眼睛、肝脏、体腔脂肪、肠道和大脑的外部和内部出血。组织学检查显示脾炎、枝节炎、全眼球炎、肝炎、肠炎和体腔炎，评估的鱼之间存在不同程度的组织损伤。从感染的鳟鱼中分离出纯海鱼利斯特氏菌菌落，并使用海鱼利斯特氏菌的特异性 PCR 引物确认了初步诊断。多位点序列分析表明，从患病鳟鱼中回收的菌株代表了一个新的遗传群。分离株能够在 24 小时内形成生物膜，从而提高了对过氧化氢消毒的抵抗力。通过腹腔内注射海鱼利斯特氏菌的系列稀释液，评估了在虹鳟鱼（Onchorhyncus mykiss）中诱导利斯特氏菌病的实验室挑战方法。攻毒后 21 天的中位致死剂量约为 20 个集落形成单位/鱼。实验感染的鳟鱼表现出与自然疾病相似的临床症状、大体变化和显微镜下病变，满足科赫假设，证明了回收菌株的高毒力。
