Echinococcus spp

Fernandez, V., Zavala, A. and Musto, H. (2001) Evidence for translational selection in codon usage in Echinococcus spp. Parasitology 123, 203-209. 

A feature of the research carried out on the physiology of the group is the relatively small number of species investigated - most experiments being carried out on Hymenolepis spp., Taenia spp., Moniezia spp., Echinococcus spp. and Mesocestoides spp. amongst the Cyclophyllidea, and various species of Diphyllobothriidae amongst the Pseudophyllidea. 

Some useful, general studies on intermediary metabolism include those on Monieziaexpansa (59-61,664) H. diminuta (400,531,590,612,667) H. microstoma (665, 666) Echinococcus spp. (488, 498, 500) Mesocestoides corti (399) Cotugnia digonopora (618, 619) Schistocephalus solidus (406) and Ligula intestinalis (502). 

The phenomenon of biochemical strain variation in helminths is proving of increasing interest to parasite biochemists and the area has been comprehensively reviewed by Bryant Flockhart (104). Probably the most remarkable examples of strain variation in cestodes occur in the hydatid organisms, Echinococcus spp. Accounts of the biochemistry and physiology (492) and the extent and significance of strain variation (501, 865) are available for this group. 

Fig. 5.8. Respiratory pathways in Echinococcus spp., sites of ATP synthesis (ox) oxidative, and (red) reductive processes PK, pyruvate kinase OAA, oxaloacetate ME(c), ME(m), malic enzyme (cytosolic) or (mitochondrial) FR, fumarate reductase PDH, pyruvate dehydrogenase complex. (After McManus Bryant, 1986.)...

It has been purified (445) and shares some properties in common with malic enzymes from mammals and birds in being NADP-dependent, heat-stable and able to decarboxylate oxaloacetate. The malic enzyme of H. microstoma also has a marked specificity for NADP (216), contrasting with that of Spirometra mansonoides, which appears to be both NAD- and NADP-linked (220). Malic enzyme has been demonstrated in a range of other cestodes including Mesocestoides corti (399), Schistocephalus solidus (406), Moniezia expansa (60), Echinococcus spp. (500) and L. intestinalis (502). 

In general it is difficult to assess experimentally the importance of the TCA cycle to the energy budget of cestodes, since, as we have seen, partly oxidised metabolites are excreted as end-products even under aerobic conditions. Notwithstanding, there is increasing evidence that, under aerobic conditions, certain cestodes such as Schistocephalus solidus (406) and Echinococcus spp. (500) are capable of catabolising substantial... 

The total protein content of cestodes is lower than that of most invertebrates being generally between 20% and 40% of the dry weight (796), although values of over 60% have been reported for Echinococcus spp. (488, 498) (Table 4.1). 

Most work on protein polymorphism in cestodes has undoubtedly been performed with the hydatid organisms Echinococcus spp., because their identification presents a number of challenging problems. The life cycles involve various hosts while much inter- and intra-specific variation occurs and this has important implications for the epidemiology of hydatid disease (495, 501, 865). 

These are normally embryonated when laid so that embryonation is not affected by external environmental factors. On account of their important role in the epidemiology of cestodiasis, the effect of environmental factors has been much studied. In particular, the effect of various physico-chemical factors on the viability of eggs of Echinococcus spp. and Taenia spp. in soil, on pastures or in sewage has been extensively reviewed (82,106, 252, 253, 638,825,963,968,969). Results of some of these studies are summarised in Tables 7.7 and 7.8). 

Echinococcus spp. culture of asexual (cystic) and sexual (strobilar)... 

ECHINOCOCCUS SPP. DEVELOPMENT OF MONOZOIC AND OTHER ABNORMAL FORMS IN CULTURE... 

It is beyond the scope of this text to consider the immunodiagnosis of adult and larval cestode infections. Various aspects of this topic have been extensively reviewed by Flisser et al. (226), Fox et al. (228), Draper Lillywhite (183), Houba (337), Gottstein et al. (261), Rickard Lightowlers (690) and Walls Schantz (928). A major breakthrough in diagnosis has been the development of an anti-oncospheral monoclonal antibody for the unequivocal identification of eggs of Echinococcus spp. by immunofluorescence (154). 

McManus, D. P., Knight, M. Simpson, A. J. G. (1985). Isolation and characterisation of nucleic acids from the hydatid organisms Echinococcus spp. (Cestoda). Molecular and Biochemical Parasitology, 16 251-66. 

Echinococcus spp., Diphyllobothrium latum and Spirometra erinacei (cats, dogs) and Raillietina spp., Hymenolepis spp., Dicranotaenia spp. and Choanofaenia infundibulum (birds). A few tapeworms such as Stilesia hepatica and Thysanosoma actinioides are found in the bile duct of cattle. 

Praziquantel stimulates the movement of Hymenolepis and Echinococcus spp. at low concentrations (1 ng/ ml). Higher concentrations of the drug causes rapid contraction of the worms. At a concentration of 1-10 pg/ml of praziquantel, the helminths were found to be immobilized and contracted within 10-30 seconds [26,122,123]. The tetanic contraction of the worm s musculature results in its paralysis. Fetterer and coworkers [124] have shown that the drug is capable of inducing spastic and/or paralytic effects in cestodes, trematodes and to some extent in nematodes also. 

Within each class of helminths, the best-studied organisms are described (i.e. Hymenolepis diminuta. Schistosoma mansoni, Ascaris suum) to establish general principles. Important exceptions are noted where appropriate. Comments are primarily restricted to adult stages, which generally cause the most important pathology (with some notable exceptions, e.g.. Echinococcus spp. and Onchocerca volvulus) and represent the principal targets for chemotherapy. 

Helminth parasites are the most complex infectious disease agents infecting mammals, and hence the host s antibody responses to them are the most diverse. Unlike other infectious diseases, most helminths do not divide in the body of the final host, and therefore the antigenic load is dependent on the infective dose. Exceptions to this are Echinococcus spp. and Strongyloides spp. Antibodies are produced against antigens present within helminths (somatic... 

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