Effects of diet on the development of Schistosoma mansoni in Biomphalaria glabrata and on the neutral lipid content of the digestive gland-gonad complex of the snail

Resistance of Biomphalaria alexandrina to Schistosoma mansoni and Bulinus truncatus to Schistosoma haematobium Correlates with Unsaturated Fatty Acid Levels in the Snail Soft Tissue

Only a fraction of the Biomphalaria and Bulinus snail community shows patent infection with schistosomes despite continuous exposure to the parasite, indicating that a substantial proportion of snails may resist infection. Accordingly, exterminating the schistosome intermediate snail hosts in transmission foci in habitats that may extend to kilometres is cost-prohibitive and damaging to the ecological equilibrium and quality of water and may be superfluous. It may be more cost effective with risk less ecological damage to focus on discovering the parameters governing snail susceptibility and resistance to schistosome infection. Therefore, laboratory bred Biomphalaria alexandrina and Bulinus truncatus snails were exposed to miracidia of laboratory-maintained Schistosoma mansoni and S. haematobium, respectively. Snails were examined for presence or lack of infection association with soft tissue and hemolymph content of proteins, cholesterol, and triglycerides, evaluated using standard biochemical techniques and palmitic, oleic, linoleic, and arachidonic acid, assayed by ultraperformance liquid chromatography-tandem mass spectrometry. Successful schistosome infection of B. alexandrina and B. truncatus consistently and reproducibly correlated with snails showing highly significant (up to P < 0.0001) decrease in soft tissue and hemolymph content of the monounsaturated fatty acid, oleic acid, and the polyunsaturated fatty acids, linoleic, and arachidonic acids as compared to naïve snails. Snails that resisted twice infection had soft tissue content of oleic, linoleic, and arachidonic acid similar to naïve counterparts. High levels of soft tissue and hemolymph oleic, linoleic, and arachidonic acid content appear to interfere with schistosome development in snails. Diet manipulation directed to eliciting excessive increase of polyunsaturated fatty acids in snails may protect them from infection and interrupt disease transmission in a simple and effective manner.

Effects of the Environment on Developmental Plasticity and Infection Success of Schistosoma Parasites - An Epigenetic Perspective

Evidence of how environmental cues affect the phenotypes of, and compatibility between Schistosoma mansoni and their hosts come from studies in environmental parasitology and research on host diet and chemotherapeutic treatment. Schistosomes deal with a multitude of signals from the water environment as well as cues that come from their hosts, particularly in response to molecules that serve to recognize and destroy them, i.e., those molecules that arise from their hosts' immune systems. These interactions shape, not only the parasite's morphology, metabolism and behavior in the short-term, but also their infection success and development into different stage-specific phenotypes later in their life cycle, through the modification of the parasite's inheritance system. Developmental phenotypic plasticity of S. mansoni is based on epigenetic mechanisms which are also sensitive to environmental cues, but are poorly understood. Here, we argue that specific cues from the environment could lead to changes in parasite development and infectivity, and consequently, environmental signals that come from environmental control measures could be used to influence S. mansoni dynamics and transmission. This approach poses a challenge since epigenetic modification can lead to unexpected and undesired outcomes. However, we suggest that a better understanding of how environmental cues are interpreted by epigenome during schistosome development and host interactions could potentially be applied to control parasite's virulence. We review evidence about the role of environmental cues on the phenotype of S. mansoni and the compatibility between this parasite and its intermediate and definitive 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 various larval digeneans on the calcium carbonate content of the shells of Helisoma trivolvis, Biomphalaria glabrata, and Physa sp

The calcium carbonate concentrations in the shells of Helisoma trivolvis and Physa sp. naturally infected with larval trematodes and Biomphalaria glabrata experimentally infected with larval trematodes were analyzed quantitatively. The larval trematode-snail relationships studied were H. trivolvis infected with larval Echinostoma trivolvis and Physa sp. infected with various larval digeneans, and B. glabrata infected with Echinostoma caproni or Schistosoma mansoni. The calcium carbonate concentrations of the shells of infected snails and uninfected cohorts and of the water in which the snails were maintained were determined by ion exchange chromatography. No significant differences in the calcium carbonate concentrations of shells of infected versus uninfected snails were found. The shells of B. glabrata infected with E. caproni contained significantly less calcium carbonate than the shells of uninfected B. glabrata. The hypercalcification hypothesis, i.e., larval trematodes induce an increase in the calcium concentrations in the shells of their snail hosts, was not upheld in any of the snail-larval digenean systems studied herein.

Effects of exogenous glucose on survival and infectivity of Schistosoma mansoni cercariae

The effects of exogenous glucose in artificial spring water (ASW) were studied on the survival and infectivity of Schistosoma mansoni cercariae. The mean percent survival of cercariae maintained in 1% glucose in ASW for 36 and 48 hr was significantly greater than that of cercariae maintained identically in ASW. Cercariae maintained in ASW with or without glucose for 24 hr, fixed in neutral buffered formalin, and stained in Oil Red O, showed an accumulation of neutral lipid in the tail. Cercariae maintained as described above and stained in periodic acid-Schiff exhibited depleted glycogen, mainly from the tail. Cercariae maintained in ASW with glucose for 24 hr did not resynthesize glycogen. Cercariae maintained in ASW with glucose for 24 hr were as capable of infecting male FVBN202 mice as were freshly emerged cercariae, and increased the percent of worm recovery. Exogeneous glucose added to ASW prolonged the survival of S. mansoni cercariae and increased infectivity in terms of worm recovery.