Ultrastructure and histochemistry of the metacercarial cyst of Spelotrema nicolli (Microphallidae: Trematoda)

Studies on the chemical nature of the cyst wall ofMicrophallus madrasensis

The cyst wall ofMicrophallus madrasensisresisted 6 N and 11·3 N hydrochloric acids (HCL) 36 N concentrated sulphuric acid (H2S04) and 0·35 M sodium hypochlorite. It was partially dissolved in 0·6 M sodium azide and completely dissolved in 16 N nitric acid (HNO3). An HCl hydrolysate of the cyst wall contained 10 amino acids viz. alanine, leucine, aspartic acid, glutamic acid, lysine, histidine. phenylalanine. tyrosine. cystine and proline. Polyacrylamide gel electrophoresis revealed the presence of a fast moving fraction which stained with periodic acid-Schiffs (PAS) reagent and toluidine blue was noticed in tris-glycine buffer soluble and methanol water soluble substances present in the cyst wall. Triton X-100 soluble substances present in the cyst wall revealed the presence of two slow-moving fractions stained only with PAS, and also a fast-moving fraction stained only with toluidine blue. Sodium dodecyl sulphate (SDS) soluble substances in the cyst wall revealed the presence of two fast-moving fractions which stained with PAS and toluidine blue. The slow-moving fractions are protein-bound carbohydrates. The fast-moving fractions obtained after fractionation with SDS are acid mucopolysaccharides or nucleoproteins whereas the single fraction (Triton X-100 soluble substances) which stained with toluidine blue appears to be a carbohydrate-free protein. The cyst wall ofM. madrasensisalso consisted of phospholipids and neutral lipids.

Histochemical characteristics of the metacercarial cyst wall ofGynaecotyla adunca

The cyst wall of the metacercaria ofGynaecotyla adunca(Microphallidae: Digenea) was subjected to comprehensive histochemical analysis. At the light microscope level, a uniformly thick, bipartite cyst wall, probably wholly of parasite origin, was evident. Structural modification of the cyst wall to provide an escape aperture was not apparent. The thicker, inner layer was comprised of phospholipid and glyco- and/or mucoproteins, possibly similar in structure to collagen. The outer layer was highly proteinaceous and contained additional amounts of acidic and neutral mucosubstances. The results are discussed in the context of previous observations regarding the excystment requirements of this microphallid species.

Developmental changes in the tegument of four microphallid metacercariae in their second (crustacean) intermediate hosts

The morphology of the tegument of four microphallid metacercariae from the stage of invasive cercariae to their maturation as encysted metacercariae inside their crustacean second intermediate hosts is described. The tegument of the metacercariae developed surface lamellae and projections which, along with coated vesicles in the surface syncytium, indicated that the tegument had an absorptive function. The disappearance of secretory granules from the tegument at the same time as the appearance of the first cyst wall suggested that the tegument had a role in primary cyst production. Following this, the metacercariae continued to grow and seemingly retained their absorptive ability. The tegument was also involved in the transport of material into the perimetacercarial lumen prior to its eventual inclusion in the developing inner cyst layers. It appeared that this material originated in tegumental cells located amongst the parenchymal cells beneath the tegumental syncytial layer. On completion of the secondary cyst layers there was a gradual degeneration of structures associated with absorption and a progressive accumulation of dense discoid granules traceable to underlying tegumental cells. All four microphallid species (Maritrema arenaria,M. subdolum,Levinseniella brachysomaandMicrophallus claviformis) demonstrated the same developmental pattern but the period spent in each stage differed depending on the time spent migrating to encystment sites. The pattern of tegumental development described is thought to be applicable to all microphallid metacercariae and possibly to other metacercariae which undergo growth and development in their second intermediate hosts.

The structure and formation of metacercarial cysts in the trematode family Microphallidae travassos 1920

This study deals with the formation of the metacercarial cysts of four microphallid trematodes, Maritrema subdolum, M. arenaria, Levinseniella brachysoma and Microphallus claviformis. The first observable cyst was present around Maritrema arenaria 18 h p.i. (post-infection). The other species had not developed a cyst by day 8 p.i. but their cysts were apparent by day 16 p.i. These were bi-layered and that of M. subdolum was thicker than those of L. brachysoma and Microphallus claviformis of the same age. The structure of older cysts varied substantially between the four species. Microphallus claviformis and Maritrema subdolum cysts were fully formed at 30 days p.i. Like those of M. arenaria they were bi-layered, the outer layer (up to 3 microm thick) being electron-dense and the inner one (up to 7 microm thick) being less electron-dense. The cysts of fully formed L. brachysoma metacercariae were much more complex, composed of four layers, one of which was divisible into three sub-layers. It was concluded that the outer cyst layer was the product of secretory granules which were previously identified in cercarial tegument. The inner, thicker layer was derived from several sources. These included small tegument vesicles produced over the entire surface of the metacercariae, larger fragments of tegument released from the anterio-ventral region and material liberated from the metacercarial excretory bladder. This heterogeneous material accumulated in the cyst lumen for some time before becoming polymerized to form the thick inner layer or layers of the metacercarial cysts.

A comparative ultrastructural and histochemical study of the metacercarial cyst walls of four species of Paragonimus (Troglotrematidae: Trematoda)

The metacercarial cyst walls of Paragonimus westermani, P. miyazakii, P. ohirai, and P. iloktsuenensis were examined using ultrastructural and histochemical techniques. The cyst walls of P. westermani, P. miyazakii, and P. ohirai were found to have five distinct layers, whereas the wall of P. iloktsuenensis had only two. The so-called outer cyst wall recognized on light microscopy by Miyazaki (1961) was composed of layers I-III and the so-called inner cyst wall comprised layers IV and V. The outermost layer (I) consisted of collagen fibers and probably originated from the host. Layer III detached easily from layer IV on removal of the cysts from the host tissues. Layer IV was composed of proteoglycans, and layer V consisted of protein alone. A regular hexagonal pattern in layer V appeared to be characteristic of P. westermani. Although the basic morphological patterns observed in the layers constituting the cyst walls were similar in all species examined, the thickness of each layer was apparently different. This characteristic seems to be a suitable criterion for the identification of metacercarial cysts of Paragonimus species.