Integument of the tapeworm scolex. 1. Freeze-fracture of the syncytial layer, microvilli and discoid bodies

Biochemical and ultrastructural changes in Raillietina echinobothrida in vitro exposed to extract of Lysimachia ramosa

Lysimachia ramosa (Primulaceae) is a traditionally used medicinal plant, leaves extract of which is being widely used by the Jaintia tribes of Meghalaya, India for controlling helminthiasis. Preliminary investigation carried out on helminth parasites revealed that the crude extract of the plant causes deformity in the surface topography leading to death of the parasites. Therefore, the present study was conducted to identify the specific fraction of the crude leaf extract of the plant responsible for cestocidal efficacy, through biochemical and ultrastructural studies in Raillietina echinobothrida exposed to crude extract and its different fractions namely hexane, chloroform, ethyl acetate and n-butanol. A dose dependent efficacy, with highest rate of mortality among n-butanol exposed parasites was recorded. The treated parasites exhibited complete erosion of microtriches from the tegument, disintegration of muscle bundles, cellular organelles, plasma membrane, nuclear membrane, nucleolus and vacuolization of mitochondria was also observed. Observations on histochemical distribution of some important tegumental enzymes like adenosine triphosphatase (ATPase), alkaline phosphatase (AlkPase), acid phosphatase (AcPase) and 5'Nucleotidase (5'-Nu) revealed a marked diminished stain intensity in the tegument of R. echinobothrida exposed to the crude extract and n-butanol fraction of the crude extract compared to the control. Highest reduction (77.93%) in the activity of ATPase was observed when the parasites exposed to 6 mg n-butanol fraction/ml of PBS. The results suggest that these enzymes act as target for anthelmintic stress caused by the phytochemicals present in the plant.

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.

Ultrastructure of oncosphere and early stages of metacestode development of Echinococcus granulosus

The ultrastructure of the oncospheres and developing metacestodes in vitro of Echinococcus granulosus was studied with emphasis on the origin of the laminated layer. The activated oncospheres measured 28 microns (S.D. = 1.83), and by day 5 of in vitro culture the metacestodes attained diameters up to 52 microns (S.D. = 2.66). The oncospheral plasma membrane of the tegument appeared to be formed by a microtubular cytoskeleton arranged in a predetermined pattern. By day 2 there were three main types of vesicles in the perikaryon: Vd, Vg1 and Vg2. Vesicles appeared to be synthesized in the perikaryon and continuously transported to the periphery, where the Vd vesicles could contribute to the ground substance of the syncytial tegument. We suggest that the Vg1 and Vg2 vesicles contribute to the laminated layer where, by day 5, they were seen in increased density and forming aggregations on the outer border.