Serial passages of larval Echinococcus granulosus from equine origin in mice. I. Infection with protoscolices

Differentiation of Spanish strains of Echinococcus granulosus using larval rostellar hook morphometry

Two multivariate statistical procedures (Principal Component Analysis and Discriminant Function Analysis) were used to analyse morphometric data from larval hooks of Spanish samples of Echinococcus granulosus previously characterized in physiological, biochemical and genetic studies. The 5 physical variables considered could be reduced to 2 functional variables ("length of hooks" and "number of hooks"). The number of hooks was found not to be a reliable character to differentiate between strains of this parasite. Three Spanish strains (sheep-cattle, pig, and horse strains) were identified; these results are compatible with those obtained using other techniques. We consider larval hook morphology as a valid criterion for identifying E. granulosus strains in Spain, with potential use for epidemiological studies.

Comparative cytotoxicity of secondary hydatid cysts, protoscoleces, and in vitro developed microcysts of Echinococcus granulosus

Infection with the metacestode of Echinococcus granulosus is characterized by a concomitant immunity. Survival of established and developing hydatid cysts in the intermediate host implies a mechanism to modulate its immunological reactions. In order to investigate this mechanism, secondary hydatid cysts were isolated from intraperitoneally infected laboratory white mice (strain NMRI) 12 months p.i. A number of hydatid cysts were freed from the surrounding host adventitial tissue. Monolayer cultures of non-stimulated peritoneal macrophages of NMRI mice were prepared and incubated in the presence of the hydatid cysts. By means of a trypan blue exclusion test and by measuring the incorporation of tritium labelled uridine, it was found that the presence of hydatid cysts reduced the viability of the macrophages in vitro. Toxic substances are probably secreted since the medium of cultured hydatid cysts also displayed cytotoxic activity. Hydatid cysts with adventitia, as well as culture medium of those cysts, were less toxic. When toxins, partially purified from hydatid cyst fluid, were previously incubated on a collagen coated surface, a reduced level of toxicity was found, suggesting that collagen of the host adventitia may play a role in controlling the liberation of toxins by the hydatid cyst. Virtually no toxicity was exerted by protoscoleces or by the medium of cultured protoscoleces, in contrast to in vitro vesiculated protoscoleces (so called microcysts). The results reveal a novel feature of hydatid cysts that may play a role in the survival of the parasite in the immunized host.

Development of larval Echinococcus granulosus confronted with chicken heart tissue in vitro

Vesiculated protoscoleces (VP) were produced by culturing freshly collected protoscoleces from Echinococcus granulosus horse liver hydatids in RPMI 1640 monophasic medium at 37 degrees C for 18 days. Half of the VP were used as such, the other half used after killing them by freeze-thawing. Nine-day-old chicken heart fragments (CHF) were cultured in MEM at 37 degrees C for 72 h. Subsequently, CHF were put together with live and dead VP, respectively, for up to 53 days, on a semisolid medium consisting of agar, Ringer's and MEM. Time-dependent histological observations revealed that dead VP were surrounded by CHF cells. Dead VP tissue was eventually internalized and disintegrated in about 1 week. Live VP penetrated into the CHF tissue and further developed into small hydatid cysts, located within the boundaries of the experimental 'host' tissue. The amorphous-looking contact region PAP-stained positively only with anti-E. granulosus serum and not with anti-CHF serum; it was considered identical to the normal laminated layer. The invasion of VP in CHF tissue proved to be different from a tumour or a bacterial invasion: it was concluded that the confrontation of VP and CHF had resulted in an 'in vitro cohabitation' rather than in an 'in vitro infection'.

Ultrastructural study of in vitro larval development of Echinococcus granulosus protoscoleces

Through ultrastructural study of the morphological forms developed in vitro during protoscolex culture, we describe larval E. granulosus histogenesis. The transformation of the spined microtriches in the protoscolex into truncated microtriches that develop within the hydatid cyst is discussed. The paper also describes the mitochondria location change that occurs during the evolution; the mitochondria pass from the most internal area of the distal cytoplasm along the cytoplasmic extensions into the cytoplasm of tegumental cells. The ultrastructures of both the vesiculated protoscolex and the posterior bladder demonstrate that each state corresponds to the initial step on one of the two paths of in vitro vesicular development.

Parthenogenesis and asexual multiplication among parasitic platyhelminths

Among flatworms with parasitic and commensal modes of existence, parthenogenesis and asexual multiplication appear to be largely confined to the Digenea and Cestoda, the only parasitic platyhelminths that routinely utilize indirect life-cycles. Parthenogenesis is apparently restricted to a minority of adult digeneans and cestodes inhabiting their final hosts, and a survey is made of the particular modes of parthenogenesis (i.e. apomictic, automictic and generative) which are employed by such adults. Asexual (amictic) multiplication, in the form of fissioning, is demonstrated by young adults of the cyclophyllidean cestode, Mesocestoides corti, but is otherwise not exhibited by adult cestodes or digeneans, other than in the perplexing phenomenon of proglottid formation in polyzoic tapeworms. Secondary multiplication is of ubiquitous occurrence in digenean life-cycles in the form of the proliferation which takes place within sporocysts and rediae (germinal sacs) located in the first intermediate host. The controversy concerning the nature of this multiplication is reconsidered in the context of recent findings which have centred on cellular aspects. On the basis of present evidence germinal sac multiplication should be regarded as an asexual rather than a parthenogenetic process. The cestode asexual multiplication which occurs in intermediate hosts is a function of the metacestode stage of development. Metacestode proliferation is only known from about 20 species and 6 families of polyzoic cestodes with approximately half the described instances occurring in the family Taeniidae. The organization of these proliferative metacestodes, findings concerning their totipotent stem cells and the ontogeny of buds and new scolices are all reviewed. Finally, the capacity for population expansion of multiplicative larval digeneans and metacestodes are compared, while the ecological roles and the genetical consequences of both parthenogenesis and amictic multiplication in the two taxa are also examined.

Serial passages of larval Echinococcus granulosus from equine origin in mice. III. Infections with sterile daughter cysts

Daughter cysts 0.2-3.0 mm in diameter from secondary Echinococcus granulosus cysts, collected from mice one year after experimental infection, were transferred to fresh mice. The metacestodes developed into larger cysts showing fertility and daughter cyst formation at autopsy 9-14 months post infection. The average total growth of all cysts per mouse expressed in log weight (mg) amounted to 0.25 +/- 0.03 per month. Thus, for the maintenance of the parasite in mice, daughter cysts can be used as successfully as protoscolices and small 'latent' cysts.