The early stages of Echinococcus granulosus development.

The paper points out the essential aspects of host/parasite relationship during the development of oncospheres (ONC) of Echinococcus granulosus into an early cyst. Secretions of the penetration glands in the hatched ONC causes lysis of host tissue during penetration of the activated ONC. It also protects the parasite against the host's immune response while developing the laminated layer. The microvilli, compressed under the plasma membrane in the hatched ONC, are uplifted in the activated larvae; they increase in number and size and are substituted by short and truncated microtriches in metacestodes 3 days old. At that time appears the first lamination of the laminated layer that surrounds the metacestodes as an electron-dense matrix composed of fine microfibrillated material and remnants of sloughed microvilli. The second lamination appears by day 6-8 and is more electron-dense than the first one. The laminated layer is of parasite origin, formed of a series that emanates from the germinal membrane. It is suggested that Vg secretory vesicles, that are elaborated in the perikaryon of the germinal zone and continuously carried to the syncytium via the microtubular-cytoskeleton, are responsible for the laminated layer formation and are involved in initial evasion of the immune response of the host. The cyclical production of laminations could be necessary to create layers that can ultimately be sloughed off as the cyst grows and serve to divert the host cellular response to the parasite.