Studies on the environmental adaptation of Echinococcus (Cyclophyllidea : Taeniidae) and its control

I.棘球绦虫对环境变化的适应性)棘球绦虫的分子进化：用Bootstrap分析方法检测了从不同宿主和地区分离的棘球绦虫和其他带绦虫的线粒体DNA的遗传多样性。从北海道自然感染的野生动物中分离到的多房棘球藻与阿拉斯加圣劳伦斯岛的多房棘球藻线粒体细胞色素C氧化酶亚基1(CO1)的核苷酸序列变异没有差异。这可能反映了多房棘球绦虫最近从阿拉斯加传播到北海道的情况。然而，不同地区分离的细粒棘球绦虫的co1核苷酸序列存在显著差异，遗传多样性很大，可能正在进行尾虫的物种形成。b)最终宿主的系统发育：棘球绦虫的进化适应性可以是char…更具特色的是它的主机切换策略。这在实验感染中得到了说明，以产生多房棘球绦虫的另一种最终宿主模型。在北美的啮齿动物中，属于异形菌科的Perogna osus被发现非常允许棘球绦虫在肠道内发育到绦虫期。这一观察结果与我们的假设一致，即啮齿动物可能是祖先带绦虫的最终宿主。c)棘球绦虫在中间宿主中的适应性：通过使用缺乏功能T和B淋巴细胞的严重联合免疫缺陷(SCID)小鼠，观察到脾细胞和胸腺细胞在这些动物中重建对多房棘球绦虫继发感染具有抵抗力。然而，与B细胞重建导致了更好的囊性发育。因此，免疫系统在中间宿主的多房棘球绦虫感染中可能以任何一种方式起作用。II.控制棘球绦虫在乌拉圭的细粒棘球绦虫控制程序：由细粒棘球绦虫引起的囊型包虫病在乌拉圭的流行率被认为在人口中高达3%。在接受检查的639只绵羊中，42%被发现感染了包虫病。然而，在这些感染的绵羊中，只有5%的绵羊有可育的包囊，其中含有原头节。在农村地区，绵羊每天都是由农民自己宰杀的，狗接触到受感染内脏的机会非常大。这实际上有助于延续乌拉圭细粒棘球绦虫的生命周期。对感染绵羊年龄的分析表明，感染率随着年龄的增长而成比例地增加，只有3岁及以上的绵羊才会发现含有原头节的包囊。除了继续对狗进行驱虫外，控制程序还应考虑绵羊在维持细粒棘球绦虫生活史中的重要性。b)简化狗的诊断：建立了一种基于ELISA的灵敏方法，用于检测感染细粒棘球绦虫的狗粪中的辅原抗原。该诊断可以安全地进行，不会对人类健康造成危害。辅原抗原的鉴定目前正在进行中。此外，这种蠕虫的免疫排泄机制也在调查中，最终目标是开发一种用于狗的疫苗。继这一思路之后，还在乌拉圭建立了一个由日本国际协力事业团赞助的海外合作项目。较少

I. ADAPTABILITY OF ECHINOCOCCUS TO ENVIRONMENTAL CHANGESa) Molecular evolution of Echinococcus : Mitochondrial DNA of Echinococcus as well as other taeniids, which were isolated from different hosts and regions, were examined for their genetic diversity by using the Bootstrap analysis. No difference in nuclotide sequence variation in the mitochondrial cytochrome C oxidase subunit 1 (CO1, containing about 350 base pairs) was observed between E. multilocularis which were isolated from naturally infected wildlife from Hokkaido as compared to those from St.Lawrence Island in Alaska. This may reflect the recent spread of E. multilocularis from Alaska to Hokkaido. However, significant difference in the CO1 nucleotide sequence was observed among E. granulosus which were isolated from different regions and the genetic diversity was so great that speciation of the cestode is thought to be in progress.b) Phylogeny of the definitive host : The evolutionary adaptability of Echinococcus can be char … More acterized by its strategy of host-switching. This is illustrated in experimental infections to produce an alternative definitive host model for E. multilocularis. Among the North American rodents, Perognathus, which belongs to the family Heteromydae, was found to be quite permissive to Echinococcus development to the tapeworm stage in the intestine. This observation is consistent with our hypothesis that rodents might be the definitive host of ancestral taeniids.c) Adaptability of Echinococcus in its intermediate host : By using Severe Combined Immunodeficient (SCID) mouse which lack functional T and B lymphocytes, it was observed that reconstitution with splenocytes and thymocytes invest resistance against E. multilocularia secondary infection in these animals. However, reconstitution with B cells resulted in better development of the cyst. Thus the immune system may work either way in E. multilocularis infection in its intermediate host.II. CONTROL OF ECHINOCOCCUSa) E. granulosus control program in Uruguay : The prevalence of cystic hydatid disease, which is caused by E. granulosus, in Uruguay is thought to be as high as 3% in the human population. Of the 639 sheep examined, 42% were found to be infected with hydatid cysts. However, only 5% of these infected sheep had fertile cysts which contain protoscoleces. In rural areas, sheep are slaughtered everyday by the farmers themselves and the chances of dogs having access to the infected offal is very great. This actually helps to perpetuate the life cycle of E. granulosus in Uruguay. Analysis of the age of the infected sheep shows that the infection rate proportionately increase with age, with protoscoleces-containing cysts being found only in sheep of 3 years of age and above. In addition to the continuation of the deworming of dogs, the importance of sheep in the maintenance of life cycle of E. granulosus should be also considered in the control program.b) Simplification of diagnosis in dogs : A sensitive method based on ELISA was developed for the detection of coproantigen in Echinococcus-infected dog feces. The diagnosis can be performed safely without health hazard to human. Characterization of coproantigen is presently in progress. Moreover, the mechanism of immune expulsion of the worm is also under investigation with the final objective of developing a vaccine for dogs. This line of thought is being followed up with the establishment of an oversea cooperation project sponsored by Japan International Cooperation Agency(JICA) in Uruguay. Less