Neutral lipids in cercariae, encysted metacercariae, and rediae of Echinostoma caproni

Alterations in Lipids and Minerals in Relation To Larval Trematode Infections of Nerita Polita Marine Snails

Marine snails provide an important source of vitamins, proteins, minerals, and essential fatty acids, and their mucus has a therapeutic significance. Parasitic infection of larval trematodes in these snails affects their nutritional value. The present study aimed to screen Nerita polita marine snails for the prevalence of cercarial infections and to evaluate the changes in lipids and some minerals in the infected as well as non-infected ones. Snails were collected randomly from February 2018 to January 2019 from the Red Sea Obhor bay, Jeddah city, Saudi Arabia. The amount of triglycerides, cholesterol, and phospholipids in the Digestive Gland Gonad Complex (DGG), hemolymph, and Snail Conditioned Water (SCW) of non-infected and infected Nerita polita snail was estimated using a spectrophotometer. Minerals content such as Ca, Zn, Pb, Na, Mn, Mg, K, Fe, Cu, and Cd, in the DGG and shell in the infected and non-infected snails were analyzed using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). Two types of cercariae were detected, ocellate furcocercus cercaria (Trichobilharzia regent) and xiphidiocercaria (Litorina saxatilis VII). The study showed that there is a fl uctuation in the concentration of lipids and minerals between increase and decrease in DGG, hemolymph, shell, and SCW in infected snails. The nutritive value of the snails is affected with infection through the decrease of some lipids and minerals in infected snails. Further qualitative studies are needed.

Parasite infectious stages provide essential fatty acids and lipid-rich resources to freshwater consumers

Free-living parasite infectious stages, such as motile cercariae of trematodes (flatworms), can constitute substantial biomass within aquatic ecosystems and are frequently eaten by various consumers, potentially serving as an important source of nutrients and energy. However, quantitative data on their nutritional value (e.g., essential fatty acids [EFA]) are largely lacking. As EFA are leading indicators of nutritional quality and underpin aquatic ecosystem productivity, we performed fatty acid (FA) analysis on an aggregate of ~ 30,000 cercariae of the freshwater trematode, Ribeiroia ondatrae. Individual cercariae contained 15 ng of total FA, and considerable quantities of EFA, including eicosapentaenoic (EPA, at 0.79 ng cercaria^-1) and docosahexaenoic (DHA, at 0.01 ng cercaria^-1) acids. We estimated annual EFA production by R. ondatrae cercariae for a series of ponds in California to be 40.4-337.0 μg m^-2 yr^-1 for EPA and 0.7-6.2 μg m^-2 yr^-1 for DHA. To investigate viability of cercariae as prey, we also compared growth and FA profiles of dragonfly larvae (naiads of Leucorrhinia intacta) fed equivalent masses of either R. ondatrae or zooplankton (Daphnia spp.) for 5 weeks. Naiads raised on the two diets grew equally well, with no significant differences found in their EFA profiles. While zooplankton are widely recognized as a vital source of energy, and an important conduit for the movement of EFA between algae and higher trophic levels, we suggest a similar role for trematode cercariae by 'unlocking' EFA from the benthic environment, highlighting their potential importance as a nutrient source that supports animal health.

Free-living parasite infectious stages promote zooplankton abundance under the risk of predation

Free-living parasite infectious stages, such as the cercariae of trematodes (flatworms), can represent substantial biomass in aquatic ecosystems, yet their interactions with other planktonic fauna are poorly understood. Given that cercariae are consumed by various aquatic predators, sometimes even preferentially over zooplankton, their presence may decrease predation pressure on free-living organisms within similar trophic niches by serving as alternate prey. Here, we experimentally examined how the presence of cercariae (Plagiorchis sp.) affected the population dynamics of common freshwater zooplankton (Daphnia sp.) in the presence of a predator (the larval dragonfly, Leucorrhinia intacta) known to consume both. After seeding 48 mesocosms with starting populations of Daphnia, we used four treatments (12 replicates each) representing a factorial combination of the absence/presence of both cercariae and dragonfly larvae and tracked Daphnia populations over 4 weeks. We found a significant interaction between the presence of cercariae and predators on Daphnia population size. When faced with predation pressure, Daphnia reached ~ 50% higher numbers when accompanied by cercariae than without, suggesting a "protective" effect of the latter by acting as substitute prey. Within aquatic ecosystems, an abundance of trematodes may prove advantageous for zooplankton communities that share common predators, but further studies will be needed to determine how this varies depending on the predator, trematode, and zooplankton taxa involved.

The use of echinostomes to study host-parasite relationships between larval trematodes and invertebrate and cold-blooded vertebrate hosts

Echinostomes are intestinal trematodes with life cycles that are easy and inexpensive to maintain in the laboratory. For this reason, echinostomes have served for years as experimental models in different areas of parasitology. However, the usefulness of these trematodes in experimental parasitology has been under estimated. In this paper, we discuss the life cycles of echinostomes and the techniques used to maintain them in the laboratory. We further examine the characteristics of these trematodes that make them useful models for the analysis of larval parasite-host relationships. Echinostomes are useful for studies on the immunobiology of snails, host-finding processes of free-living larval stages, effects of larval trematode infections on anuran populations, and studies on analytes in the larval trematodes and their snail intermediate hosts.

High-performance thin-layer chromatographic analysis of neutral lipids and phospholipids in Biomphalaria glabrata patently infected with Echinostoma caproni

This study examined the effects of larval trematode infection on the neutral lipid and phospholipid content of Biomphalaria glabrata patently infected with the daughter rediae of Echinostoma caproni. Uninfected snails were used as matched controls. As determined by qualitative high-performance silica gel thin-layer chromatography (HPTLC), the major neutral lipids present in the whole bodies and digestive gland-gonad complexes in both snail populations were free sterols, free fatty acids, and triacylglycerols, and the major polar lipids were phosphatidylcholine and phosphatidylethanolamine. Quantitative analysis by HPTLC with visible and UV scanning reflectance densitometry showed no significant differences in the concentrations of these lipids in whole bodies of infected snails vs the controls, but the concentration of triacylglycerols in the infected digestive gland-gonad complex was significantly less than that of the uninfected. No qualitative differences in neutral lipids and phospholipids in shell or plasma samples were found between infected vs uninfected snails.

Effects of tonicity on the release of neutral lipids in Echinostoma caproni adults and observations on lipids in excysted metacercariae

High performance thin layer chromatography was used to analyze neutral lipids in worm incubates isotonic, hypotonic, and hypertonic to the intestinal habitat of adult Echinostoma caproni. Qualitative analysis revealed the presence of free sterols, free fatty acids, triacylglycerols, and a steryl ester/hydrocarbon fraction in all incubate samples. The most abundant neutral lipid fraction released into the incubation medium was the triacylglycerol fraction. This fraction was quantified after worms were maintained for 2 h at 37.5 degrees C in hypertonic (Locke's 2x solution), isotonic (Locke's 0.5x solution) and hypotonic (deionized water) media. Percentages of triacylglycerols on a wet-weight basis found in Locke's 2x, 0.5x, and deionized water were 0.369, 3.23, and 0.242, respectively, suggesting that the optimal medium to obtain maximal excretory-secretory products is the Locke's 0.5x solution. Histochemical staining of whole excysted metacercariae with oil red O did not detect neutral lipids. Analysis of 500 excysted metacercariae incubated for 2 h at 37.5 degrees C revealed that free sterols, free fatty acids, and triacylglycerols were released in amounts of 16.2, 1.59, and 5.34 ng/organism, respectively. Our results were compared with previous studies on neutral lipids in excysted metacercariae and adults of E. trivolvis. Variations in the results of our study compared with others reflect intrinsic differences in the species of echinostome used.

Recent Advances in the Biology of Echinostoma species in the “revolutum” Group

This review examines the significant literature on the biology of Echinostoma species in the "revolutum" group. We have considered 10 species belonging to this group. There is a considerable body of literature for four of the species, i.e. Echinostoma caproni, E. trivolvis, E. paraensei and E. revolutum. For these species we have arranged coverage to include the following headings: (1) systematic and descriptive studies; (2) experimental, manipulative and ecological studies; (3) physiological and biochemical studies; (4) immunological and molecular studies. For the remaining six species, i.e. E. friedi, E. miyagawai, E. echinatum, E. parvocirris, E. luisyrei and E. jurini, the literature is not very extensive, and headings were not used. Considerable information in various areas of modern parasitology can be obtained from species in the "revolutum" complex for which the entire life cycle is maintained in the laboratory. The review includes a list of researchers and their addresses who currently maintain such life cycles.

Emergence of cercariae of Echinostoma caproni and Schistosoma mansoni from Biomphalaria glabrata under different laboratory conditions

Release of Echinostoma caproni cercariae and Schistosoma mansoni from experimentally infected Biomphalaria glabrata snails maintained under different laboratory conditions was studied. Infected snails were isolated individually for 1 h in Stender dishes containing 5 ml of artificial spring water and the number of cercariae released during this time was recorded. Of numerous conditions tested, the addition of lettuce, the use of water conditioned by B. glabrata snails and a temperature of 35 degrees C significantly increased the release of E. caproni cercariae. A significant increase in cercarial release of S. mansoni was seen only in cultures fed lettuce. A temperature of 12 degrees C caused a significant decrease in cercarial release of both E. caproni and S. mansoni. Increased snail activity associated with feeding behaviour was probably responsible for the enhanced cercarial sheds observed in this study.