Rao Shreesha, Pham Trung Hieu, Poudyal Sayuj, Cheng Li-Wu, Nazareth Sandra Celenia, Wang Pei-Chi, Chen Shih-Chu
Department of Veterinary Medicine, College of Veterinary Medicine, National Pingtung University of Science and Technology, Pingtung, Taiwan.
International Degree Program of Ornamental Fish Technology and Aquatic Animal Health, International College, National Pingtung University of Science and Technology, Pingtung, Taiwan.
Transbound Emerg Dis. 2022 May;69(3):1197-1211. doi: 10.1111/tbed.14083. Epub 2021 Apr 27.
The diseased cage-cultured cobia (Rachycentron canadum) displayed clinical signs, haemorrhagic eyes, dorsal darkness and gross pathological lesions, enlargement of spleen and liver. Haemorrhages were found in brain, heart and liver with cumulative mortality rates ranging from 20% to 50%. Extensive congestion in the heart, liver, spleen, kidney and brain was observed histopathologically. Epicarditis and meningitis were also revealed in diseased cobia. All isolates recovered from the organs (liver, spleen, head kidney, posterior kidney, brain and muscle) of cobia were found to be gram-positive, non-motile, ovoid cocci, short-chain-forming (diplococci) and α-haemolytic. The API 32 strep system together with the polymerase chain reaction assay for species-specific primers (pLG1 and pLG2) and the internal transcribed spacer (ITS) region (G1 and L1 primers) confirmed all four selected isolates as Lactococcus garvieae. Partial 16S rDNA nucleotide sequence (~1,100 bp) of one representative L. garvieae isolate AOD109191 (GenBank accession number, MW328528.1) shared 99.9% identities with the 16S rDNA nucleotide sequence of L. garvieae (GenBank accession numbers: MT604790.1). Transmission electron microscopy (TEM) evaluation of one representative L. garvieae isolate (AOD109191) and the results of multiplex PCR did not reveal the presence of the capsular gene cluster (CGC), thus categorizing the isolate as the KG+ phenotype. Capsule staining and TEM observations confirmed the presence of a hyaluronic acid-like capsule, a possible virulence factor in KG+ phenotype L. garvieae isolates. The pathogenic potential of the representative isolate (AOD109191) was assessed through intraperitoneal injection challenges in cobia. The gross lesions and histopathological changes found in experimentally infected cobia were similar to those seen in naturally infected fish. This is the first report that confirms L. garvieae-induced 'warm water lactococcsis' can cause outbreaks of diseases in cage-cultured cobia.
患病的网箱养殖军曹鱼（Rachycentron canadum）出现了临床症状，眼睛出血、背部颜色变深以及明显的病理损伤，脾脏和肝脏肿大。在脑、心脏和肝脏中发现出血，累计死亡率在20%至50%之间。组织病理学观察发现心脏、肝脏、脾脏、肾脏和脑有广泛充血。患病军曹鱼还出现了心外膜炎和脑膜炎。从患病军曹鱼的器官（肝脏、脾脏、头肾、后肾、脑和肌肉）中分离出的所有菌株均为革兰氏阳性、不运动、卵形球菌、形成短链（双球菌）且α溶血。API 32链球菌系统以及针对种特异性引物（pLG1和pLG2）和内转录间隔区（ITS）区域（G1和L1引物）的聚合酶链反应分析证实，所选的4株分离株均为加氏乳球菌（Lactococcus garvieae）。一株代表性的加氏乳球菌分离株AOD109191（GenBank登录号MW328528.1）的部分16S rDNA核苷酸序列（约1100 bp）与加氏乳球菌的16S rDNA核苷酸序列（GenBank登录号：MT604790.1）有99.9%的同源性。对一株代表性的加氏乳球菌分离株（AOD109191）进行的透射电子显微镜（TEM）评估以及多重PCR结果未显示存在荚膜基因簇（CGC），因此将该分离株归类为KG+表型。荚膜染色和TEM观察证实存在一种透明质酸样荚膜，这可能是KG+表型加氏乳球菌分离株的一种毒力因子。通过对军曹鱼进行腹腔注射攻毒试验评估了代表性分离株（AOD109191）的致病潜力。在实验感染的军曹鱼中发现的大体病变和组织病理学变化与自然感染鱼中所见相似。这是首次证实加氏乳球菌引起的“温水乳球菌病”可导致网箱养殖军曹鱼疾病暴发的报告。
