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

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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