寄生于两种湖泊淡水鱼的伊格诺图斯胃瘤线虫Ⅳ期幼虫PCR分析、形态结构和组织病理

PCR analysis and morphology of the fourth-stage larvae of Eustrongylides ignotus and histopathology of two infected fishes in freshwater lake

为探明寄生于翘嘴鲌(Culter alburnus Basilewsky)和花?(Hemibarbus maculatus Bleeker)腹腔内线虫的分类地位、形态特征及其寄生部位的组织损伤作用,进行了18S rDNA和ITS rDNA序列的PCR分析以及虫体和组织病理的显微观察。结果表明该线虫为伊格诺图斯胃瘤线虫(Eustrongylides ignotus)的IV期幼虫,明确了其ITS rDNA的基因序列。虫体除头部具有6个棘状突起和6个乳头状突起以及尾部具有尾斑突外,还发现其具有凹纹的体侧斑突等一些新的形态结构特征,补充了一些主要形态结构数据。根据体肌肌细胞数量和其一端伸入体腔的特点判定线虫体肌属于多肌型。食道由背侧腺和下腹腺组成,食道腔横切面呈三放射形。依据组成肠道的单层柱状上皮细胞数量,判定该线虫肠道属于多胞型。卵巢、输卵管、精巢和输精管外层均由以纤维细胞为主要成分的结缔组织构成。病理观察显示部分线虫以包囊形式寄生于肝脏、肠系膜和脾脏的腹腔组织器官,形成由纤维细胞和血管组成的包囊和大量嗜酸性白细胞浸润的主要炎症反应,包囊经历了形成、增大、壁增厚和后期包囊壁中细胞坏死而破裂的过程,严重感染的个体出现肝脏充血、细胞坏死和含铁血黄素沉着,脾脏缺血和含铁血黄素沉着以及肠系膜中的胰腺细胞分泌颗粒增多等病理变化。结果表明,该IV期幼虫对寄主内脏组织器官具有不同程度的组织病理损伤作用。

To determine the taxonomic status,characteristics,and histopathology of nematodes infecting the intraperitoneal tissues and organs of Culter alburnus Basilewsky and Hemibarbus maculatus Bleeker,PCR analysis were used to evaluate 18S rDNA and ITS rDNA sequences and microscopic observations were used to evaluate nematode morphology and histopathology.Nematodes were identified as the fourth-stage larvae of Eustrongylides ignotus and their ITS rDNA sequences were confirmed.Six spinous papilla and six papillary papilla were identified in the cephalic extremity and caudal plaques in the posterior of E.ignotus.In addition,data were supplemented,and new characteristics of morphological structures,including lateral plaques with grooves,were identified.Their body muscles were of the polymyarian type according to the number of muscle cells and their characteristics at one end of the body,which stretched into the coelom.The esophagus consisted of a dorsal gland,ventral glands,and a three-radiate esophageal lumen.The intestine was more cell type according to the number of monolayer columnar epithelial cells in the intestine.The outer layers of the ovary,oviduct,testis,and spermaduct were composed of connective tissue mainly with fibrocytes.Histopathological observations revealed that some nematodes infected the liver,mesentery,and spleen,with the formation of cysts in the abdominal cavity of fish.The main inflammatory responses were the formation of cysts,which were mainly composed of fibrocytes,blood vessels,and many infiltrated eosinophilic leukocytes.The cyst underwent formation,wall thickening,enlargement,cell wall necrosis,and rupture in the late stage.Severely infected livers appeared congested,with cell necrosis and hemosiderosis.The spleen presented ischemia and hemosiderosis.Secretory granules of pancreatic cells in the mesentery were increased.Thus,infection with the fourth-stage larvae of E.ignotus induces different degrees of histopathological changes in the internal organs of host fish.