Reimschuessel R, Gieseker C M, Driscoll C, Baya A, Kane A S, Blazer V S, Evans J J, Kent M L, Moran J D W, Poynton S L
US Food and Drug Administration, Center for Veterinary Medicine, Office of Research, Laurel, Maryland 20708, USA.
Dis Aquat Organ. 2003 Feb 13;53(2):143-66. doi: 10.3354/dao053143.
Ulcers in Atlantic menhaden Brevoortia tyrannus (Latrobe) (Clupeidae), observed along the USA east coast, have been attributed to diverse etiologies including bacterial, fungal and, recently, harmful algal blooms. To understand the early pathogenesis of these lesions, we examined juvenile Atlantic menhaden collected during their seasonal presence in Chesapeake Bay tributaries from April to October 1999 and from March to August 2000. We conducted histopathological examinations of young-of-the-year fish from the Pocomoke River tributary, which has a history of fish mortalities and high lesion prevalence. Kudoa clupeidae (Myxozoa: Myxosporea) spores were present in the muscles of fish collected in both years. Of the fish assessed by histology in April, 5 to 14% were infected, while in May 90 to 96% were infected. Infection rates remained high during the summer. Mature spores were primarily located within myomeres and caused little or no observable pathological changes. Ultrastructure showed spores with capsulogenic cells bearing filamentous projections, and a basal crescentic nucleus with mottled nucleoplasm containing cleaved, condensed chromatin. Also, a highly invasive plasmodial stage of a myxozoan was found in the lesions of juvenile Atlantic menhaden. The plasmodia were observed in fish collected between May and July, with the maximum occurrence in late June 1999 and late May 2000. Plasmodia penetrated and surrounded muscle bundles, causing grossly observable raised lesions in 73% of all fish infected with this invasive stage. Plasmodia were also detected in the visceral organs, branchial arches, and interocular muscles of some fish. Some of the invasive extrasporogonic plasmodial lesions were associated with ulcers and chronic inflammatory infiltrates. The plasmodial stage appeared to slough out of the tissue with subsequent evidence of wound healing. Ultrastructure showed plasmodia with an elaborate irregular surface, divided into distinct ectoplasm and endoplasm; the latter contained numerous spherical vegetative nuclei, secondary generative cells, and occasional cell doublets. Our ultrastructural studies indicate that the plasmodial organisms, which are important in the etiology of the skin lesions, are myxozoans, and they may represent early stages of K. clupeidae.
在美国东海岸观察到的大西洋油鲱（Brevoortia tyrannus (Latrobe)，鲱科）溃疡，其病因多种多样，包括细菌、真菌，以及最近发现的有害藻华。为了解这些损伤的早期发病机制，我们检查了1999年4月至10月以及2000年3月至8月在切萨皮克湾支流季节性出现期间采集的幼年大西洋油鲱。我们对波科莫克河支流当年幼鱼进行了组织病理学检查，该支流有鱼类死亡和高损伤发生率的历史。两年采集的鱼的肌肉中均存在库多黏体虫（Kudoa clupeidae，粘孢子虫纲：粘孢子目）孢子。4月经组织学评估的鱼中，5%至14%受到感染，而5月感染率为90%至96%。夏季感染率仍然很高。成熟孢子主要位于肌节内，几乎没有或没有引起明显的病理变化。超微结构显示孢子带有具丝状突起的成囊细胞，以及一个基部新月形细胞核，核质斑驳且含有裂解、浓缩的染色质。此外，在幼年大西洋油鲱的损伤部位发现了粘孢子虫的一个高度侵袭性的变形体阶段。在5月至7月采集的鱼中观察到了变形体，1999年6月下旬和2000年5月下旬出现的数量最多。变形体穿透并包围肌束，在所有感染此侵袭阶段的鱼中，73%出现了肉眼可见的隆起损伤。在一些鱼的内脏器官、鳃弓和眼间肌中也检测到了变形体。一些侵袭性的孢子外发育变形体损伤与溃疡和慢性炎症浸润有关。变形体阶段似乎从组织中脱落，随后有伤口愈合的迹象。超微结构显示变形体表面精细不规则，分为明显的外质和内质；内质包含许多球形营养核、次生生殖细胞和偶尔出现的细胞双联体。我们的超微结构研究表明，在皮肤损伤病因中起重要作用的变形体生物是粘孢子虫，它们可能代表库多黏体虫的早期阶段。
