鲑鱼隐鞭虫病及其防治策略(英文)

Salmonid cryptobiosis and strategies against the disease

鲑鱼隐鞭虫病的病原为Cryptobiasalmositica。据报道,北美西海岸的所有大西洋鲑(Oncorhynchusspp.)均有该虫的寄生。该病除了通常情况下经河流中的水蛭传播外,在特定的条件下可直接经鱼类传播。鲑隐鞭虫病的临床症状包括贫血、食欲减退、脾脏肿大、全身性水肿、腹水性腹胀。被感染的鱼类需要付出巨大的能量代价,表现出明显的新陈代谢及游泳功能的衰退。鱼体对缺氧相当敏感,免疫系统也受到抑制。鱼类对隐鞭虫病的感染严重程度和死亡率可因鱼种而存在差异。预防感染的有效策略包括选育抗隐鞭虫的新品种,“抗隐鞭虫感染”在遗传上是孟德尔显性遗传。在抗隐鞭虫的鱼体内,虫体可被宿主免疫系统的“补体旁路途径”所裂解。在“隐鞭虫耐受性鱼”(处于感染状态但未发病)的血液中存在一种天然的抗蛋白酶———α2巨球蛋白,可以中和分泌的金属蛋白酶(毒力因子)。因此,繁殖转基因“隐鞭虫耐受性”鲑鱼是一种很好的选择,而无需通过疫苗和药物来治疗隐鞭虫病。康复后的鱼体具有对该病的免疫保护力,因而,利用这一特点采取疫苗免疫也是防治隐鞭虫病的另一种策略。我们所研制的致弱疫苗单一剂量免疫鱼体可获得至少两年的免疫保护。免疫保护机制包括产生“抗体结合补体”、强化吞噬作用及细胞介导的细胞毒作用。氯化氮氨菲啶是防治隐鞭虫病的有效药物,它通过溶解虫体而杀灭寄生虫,也可在线粒体中富集,显著影响有氧呼吸的顺利进行并造成线粒体的损伤。通过药物与抗体连接可以显著增强药效,这种利用“免疫化学疗法”控制鲑隐鞭虫病的策略,其优点在于减小了药物剂量,因而大大降低了化学治疗所引起的副作用。对于食用性鱼类而言。

Salmonid cryptobiosis is caused by Cryptobia salmositica. The haemoflagellate has been reported from all species of Pacific salmon （ Oncorhynchus spp. ） on the west coast of North America. It is normally transmitted by freshwater leeches in streams and rivers; however, under certain conditions direct transmission between fish can occur. Clinical signs of the disease include anaemia, anorexia, splenomegaly, general oedema, and abdominal distension with ascites. The metabolism and swimming performance of infected fish are significantly reduced and the bioenergetic cost of the disease is very considerable. Infected fish are susceptible to hypoxia and their immune system is depressed. Severity of the disease and mortality vary greatly between species and stocks of salmon. Protective strategies include selective breeding of Cryptobia-resistant fish. This is resistance to infection, and it is controlled by a dominant Mendelian locus. In resistant fish the parasite is lysed via the Alternative Pathway of Complement Activation. In Cryptobia-tolerant fish （infected with the pathogen but do not suffer from disease） the secreted metalloprotease （virulent factor） is neutralized by α2 macroglobulin, a natural anti-protease that is in the blood. Production of transgenic Cryptobia-toterant salmon is an option. This strategy has the advantage in that human intervention （e. g. , vaccination, chemotherapy） is not required once the transgenic fish is produced. Fish that have recovered from cryptobiosis are protected, consequently acquired immunity is another option. We have an attenuated life vaccine and a single dose of the vaccine protects fish for at least two years. The protective mechanism involves production of complement fixing antibodies, enhanced phagocytosis, and cell-mediated cytotoxicity. The drug isometamidium chloride, is an effective therapeutic and prophylactic agent. It lyses the parasite, and it also accumulates in its mitochondrion to significantly disrupts aerobic respiration by causing lesions in the organelle. Efficacy of the drug is significantly increased after its conjugation to antibodies. This immuno-chemotherapeutic strategy has the advantage in that it lowers the drug dosage and hence side effects of chemotherapy. It will also reduce the accumulation of the drug in fish tissues, and this is aim an important consideration in food fish [ Acta Zoologica Sinica 51 （4） ： 546-549, 2005].