The penetration of Fascioloides magna miracidia into the snail host Fossaria bulimoides. A scanning electron microscope study

In Vitro Effects of Mucus from the Mantle of Compatible (Lymnaea elodes) and Incompatible (Helisoma trivolvis) Snail Hosts on Fascioloides magna Miracidia

The epidermal mucus covering the surface of a snail represents an important barrier to trematode larvae attempting to penetrate the snail and may play a role in mediating snail-trematode compatibility. In this study, Facioloides magna miracidia were exposed to mucus harvested from a compatible snail host, Lymnaea elodes (palustris), and from an incompatible snail, Helisoma trivolvis . In vitro treatment of freshly hatched miracidia with snail-derived mucus exerted dramatically different effects on larvae depending on snail species. At the lowest dilution of mucus tested (1:3) mean damage rates (tegumental damage and/or larval lysis and death) were as high as 100% for miracidia exposed to H. trivolvis mucus, while none of F. magna miracidia were damaged in L. elodes mucus. A dilution series for each snail species, and treatments with heat and proteinase K were performed to characterize the component(s) of mucus inducing the observed morphological changes. The damaging effects of H. trivolvis mucus were concentration dependent and completely abrogated by heat (65 C, 30 min) and proteinase treatment, strongly implicating a heat-labile protein(s) in mucus as the active cytotoxic agent(s). In contrast to our prediction that miracidial contact with mucus of compatible L. elodes would trigger larval transformation, mucus from either snail species tested exhibited little to no activity. Overall these data demonstrate the presence of a potent cytotoxic protein-like factor in the mucus of F. magna -incompatible H. trivolvis , and its absence in the mucus of the compatible snail, L. elodes . This finding supports the notion that the epidermal mucus layer may be serving as an important determinant of larval trematode-snail compatibility.

A deep exploration of the transcriptome and "excretory/secretory" proteome of adult Fascioloides magna

Parasitic liver flukes of the family Fasciolidae are responsible for major socioeconomic losses worldwide. However, at present, knowledge of the fundamental molecular biology of these organisms is scant. Here, we characterize, for the first time, the transcriptome and secreted proteome of the adult stage of the "giant liver fluke," Fascioloides magna, using Illumina sequencing technology and one-dimensional SDS-PAGE and OFFGEL protein electrophoresis, respectively. A total of ∼54,000,000 reads were generated and assembled into ∼39,000 contiguous sequences (contigs); ∼20,000 peptides were predicted and classified based on homology searches, protein motifs, gene ontology, and biological pathway mapping. From the predicted proteome, 48.1% of proteins could be assigned to 384 biological pathway terms, including "spliceosome," "RNA transport," and "endocytosis." Putative proteins involved in amino acid degradation were most abundant. Of the 835 secreted proteins predicted from the transcriptome of F. magna, 80 were identified in the excretory/secretory products from this parasite. Highly represented were antioxidant proteins, followed by peptidases (particularly cathepsins) and proteins involved in carbohydrate metabolism. The integration of transcriptomic and proteomic datasets generated herein sets the scene for future studies aimed at exploring the potential role(s) that molecules might play at the host-parasite interface and for establishing novel strategies for the treatment or control of parasitic fluke infections.

Morphological characterization of adult Fascioloides magna (Trematoda: Fasciolidae): first SEM report

Five adult Fascioloides magna specimens were recovered from the livers of naturally infected calves from Texas, USA. Scanning electron microscopy was used to study the morphological characteristics of the trematodes. These mature flukes measured 35-100 mm in length by 15-25 mm in width and had an oval dorsoventrally flattened body, with no anterior cone. The tegument was armed with sharp spines. Around the oral and ventral suckers, some of the spines were small, with a sharp point, while others had serrated edges with 15-22 sharp points. The surface of the oral sucker was covered by an interesting pattern of tegument, small dome-shaped and ciliated papillae. The ventral sucker showed a smooth surface and two unknown spine-like structures. There were fewer spines at the base of the genital pore than on other parts of the anterior end of the worm. At the anterior end of the ventral side, well-developed spines were observed, while at the posterior end of the ventral side, the spines were small, mostly with one or three points and blunted edges. At the posterior end of the dorsal side, the spines became progressively fewer, smaller, and shorter. Around the excretory pore, the tegument was folded, with no spines, and small groups of dome-shaped and ciliated papillae were present. The cirrus organ showed a smooth surface, with small pores on the dorsal side and small groups of tiny spines between the folds. The eggs measured 168 × 101 μm and had a protoplasmic appendage at the pole opposite the operculum. At the posterior end of the dorsal side, and toward the right, a pore with a very thin rim was present, which could be the terminus of Laurer's canal.

Miracidial penetration in Fascioloides magna (Trematoda)

The penetration of the miracidium of Fascioloides magna into the snail host Fossaria bulimoides is followed by examining the process at certain, timed intervals during the course of penetration. The cilia are lost early, but the epithelial cells may detach or they may be carried into the snail body. The apical gland releases vesicles which lose their outer coat in the snail tissue; similarly the vesiculated gland cells release vesicles which lose their coating in the snail tissue where there is a concomitant destruction of snail collagen fibers. Evidence is presented to support the concept of both a mechanical and an enzymatic penetration of snail tissues. Both transmission and scanning electron micrographs are used.

The penetration of Fasciola hepatica miracidia into the snail host Fossaria bulimoides. A scanning electron microscope study

Snails of the species Fossaria bullimoides were exposed to miracidia of Fasciola hepatica for given periods of time. The course of penetration was followed by means of scanning electron microscopy. Topographical features of miracidial morphology were studied with emphasis on epidermal plates and body shape. Comparisons are made on the rate of penetration into this snail host.