Molluscicidal effect of nicotinanilide and its intermediate compounds against a freshwater snail Lymnaea luteola, the vector of animal schistosomiasis

The molluscicidal effect of nicotinanilide was evaluated and compared with niclosamide (2',5-dichloro-4'-nitrosalicylanilide, ethanolamide salt) against different stages of the freshwater snail Lymnaea luteola i.e., eggs, immature, young mature, and adults. Calculated values of lethal concentrations (LC50 and LC90) showed that both nicotinanilide and niclosamide as toxic against eggs, immature, and adults. The young mature stage of the snails was comparatively more tolerant to both molluscicides than the other stages. The toxicity of the intermediate compounds of nicotinanilide against the young mature stage of the snails showed them as ineffective. The mortality pattern of the snails exposed to LC90 concentration of these molluscicides showed niclosamide to kill faster (within 8 to 9 h) than nicotinanilide (26 to 28 h). In view of the above studies it may be concluded that both molluscicides are toxic against all the stages of the L. luteola snails.     

Usnic Acid Potassium Salt: An Alternative for the Control of Biomphalaria glabrata (Say, 1818)

In Brazil, the snail Biomphalaria glabrata is the most important vector of schistosomiasis due to its wide geographical distribution, high infection rate and efficient disease transmission. Among the methods of schistosomiasis control, the World Health Organization recommends the use of synthetic molluscicides, such as niclosamide. However, different substances of natural origin have been tested as alternatives for the control or eradication of mollusks. The literature describes the antitumor, antimicrobial and antiviral properties of usnic acid as well as other important activities of common interest between medicine and the environment. However, usnic acid has a low degree of water solubility, which can be a limiting factor for its use, especially in aquatic environments, since the organic solvents commonly used to solubilize this substance can have toxic effects on aquatic biota. Thus, the aim of the present study was to test the potassium salt of usnic acid (potassium usnate) with regard to molluscicidal activity and toxicity to brine shrimp (Artemia salina). To obtain potassium usnate, usnic acid was extracted with diethyl ether isolated and purified from the lichen Cladonia substellata. Biological assays were performed with embryos and adult snails of B. glabrata exposed for 24 h to the usnate solution solubilized in dechlorinated water at 2.5; 5 and 10 µg/ml for embryos, 0.5; 0.9; 1;5 and 10 µg/ml for mollusks and 0.5; 1; 5; 10 µg/ml for A. salina. The lowest lethal concentration for the embryos and adult snails was 10 and 1 µg/ml, respectively. No toxicity to A. salina was found. The results show that modified usnic acid has increased solubility (100%) without losing its biological activity and may be a viable alternative for the control of B. glabrata.     

Histopathological Changes in Tissues of Bithynia siamensis goniomphalos Incubated in Crude Extracts of Camellia Seed and Mangosteen Pericarp

The present study was performed to observe histopathological changes in tissues of Bithynia siamensis goniomphalos (Gastropoda, Bithyniidae) incubated in crude extract solutions of camellia (Camellia oleifera) seed and mangosteen (Garcinia mangostana) pericarp, and furthermore to estimate the molluscicidal effects of 2 plant substances. Substantial numbers of bithyniid snails were incubated in various concentrations of 2 plant solution for 24 hr. As the positive control, snails incubated in various concentrations of niclosamide, a chemical molluscicide, were used. The histopathological findings were observed in sectioned snail specimens of each experimental and control groups. The results showed that both camellia and mangosteen extracts had molluscicidal effects at 24 hr with 50% lethal concentration (LC₅₀) at concentrations of 0.003 and 0.002 g/ml, respectively, while niclosamide had LC₅₀ at concentrations 0.599 ppm. B. siamensis goniomphalos snail tissues (foot, gill, and digestive system) showed disruption of columnar muscle fibers of the foot, reduction of the length and number of gill cilia, numerous mucous vacuoles, and irregularly shaped of epithelial cells. Irregular apical and calciferous cells, dilatation of the digestive gland tubule, and large hemolymphatic spaces, and irregular apical surfaces, detachment of cilia, and enlargement of lysosomal vacuoles of epidermis were also shown in all groups. By the present study, it is confirmed that 2 plants, camellia and mangosteen, are keeping some substance having molluscicidal effects, and histopathological findings obtained in this study will provide some clues in further studies on their action mechanisms to use them as natural molluscicides.     

Larval excretory-secretory products from the parasite <Emphasis Type="Italic">Schistosoma mansoni</Emphasis> modulate HSP70 protein expression in defence cells of its snail host, <Emphasis Type="Italic">Biomphalaria glabrata</Emphasis>

Synthesis of heat shock proteins (HSPs) following cellular stress is a response shared by many organisms. Amongst the HSP family, the ∼70 kDa HSPs are the most evolutionarily conserved with intracellular chaperone and extracellular immunoregulatory functions. This study focused on the effects of larval excretory-secretory products (ESPs) from the parasite Schistosoma mansoni on HSP70 protein expression levels in haemocytes (defence cells) from its snail intermediate host Biomphalaria glabrata. S. mansoni larval stage ESPs are known to interfere with haemocyte physiology and behaviour. Haemocytes from two different B. glabrata strains, one which is susceptible to S. mansoni infection and one which is resistant, both showed reduced HSP70 protein levels following 1 h challenge with S. mansoni ESPs when compared to unchallenged controls; however, the reduction observed in the resistant strain was less marked. The decline in intracellular HSP70 protein persisted for at least 5 h in resistant snail haemocytes only. Furthermore, in schistosome-susceptible snails infected by S. mansoni for 35 days, haemocytes possessed approximately 70% less HSP70. The proteasome inhibitor, MG132, partially restored HSP70 protein levels in ESP-challenged haemocytes, demonstrating that the decrease in HSP70 was in part due to intracellular degradation. The extracellular signal-regulated kinase (ERK) signalling pathway appears to regulate HSP70 protein expression in these cells, as the mitogen-activated protein-ERK kinase 1/2 (MEK1/2) inhibitor, U0126, significantly reduced HSP70 protein levels. Disruption of intracellular HSP70 protein expression in B. glabrata haemocytes by S. mansoni ESPs may be a strategy employed by the parasite to manipulate the immune response of the intermediate snail host.     

Schistosoma mansoni: Cytotoxicity of hemocytes from susceptible snail hosts for sporocysts in plasma from resistant Biomphalaria glabrata

Sporocysts of Schistosoma mansoni (PR1 strain) survive and grow in Biomphalaria glabrata PR albino strain snails, whereas they are encapsulated and die in B. glabrata 10R2 strain snails. These processes also occur in an in vitro system in which the only living cells are those of sporocysts and snail hemolymph. Hemocytes of the susceptible snail are normally not effective in damaging sporocysts. However, when the encounter occurred in the presence of cell-free plasma from resistant snails, previously impotent hemocytes severely damaged sporocysts in 24 hr. The cytotoxic capacity of resistant strain hemocytes was not altered by plasma from susceptible snails. Furthermore, it was retained even when plasma was replaced by culture medium free of snail components. The nature of the plasma factor(s) which facilitated damage by otherwise impotent hemocytes is discussed, and evidence is evaluated for the hypothesis that snail resistance is dependent upon the specificity of cytophilic factors present both in the plasma and on the hemocyte plasma membranes.     

Distribution and variation of hemagglutinating activity in the hemolymph of Biomphalaria glabrata

A sensitive hemagglutination assay utilizing glutaraldehyde-fixed trypsinized calf erythrocytes (GTC) is described to test for agglutinin levels in hemolymph and albumen gland extracts from nine populations of Biomphalaria glabrata, and from B. straminea and B. obstructa. High levels of GTC-reactive hemagglutinin were found in all snail populations. There was no correlation between hemagglutinin titer and innate resistance of B. glabrata strains to Schistosoma mansoni. However, an increase in hemagglutinin titer occurs in B. glabrata M-RLc snails infected with Echinostoma lindoense and in snails sensitized and reexposed to this parasite.     

14C uptake by Schistosoma mansoni from Biomphalaria glabrata exposed to 14C-glucose

Exposure of Biomphalaria glabrata infected with Schistosoma mansoni to ¹⁴C-glucose results in a greater uptake of original total snail label by the parasitized digestive gland-gonad, site of the developing daughter sporocysts and cercariae, than by the digestive gland-gonad of control animals. As a consequence of this greater uptake by the infected digestive gland-gonad, the albumen gland and remainder of the carcass of parasitized snails receive less label than do those areas in normal snails. Emergence of cercariae from the snail and daughter sporocyst mass account for a diversion of 12.6% of original total label from the infected snail itself. This diversion of label from the snail to the parasite may explain carbohydrate depletion in parasitized snails.     

Impact of the age of Biomphalaria alexandrina snails on Schistosoma mansoni transmission: modulation of the genetic outcome and the internal defence system of the snail

Of the approximately 34 identified Biomphalaria species,Biomphalaria alexandrina represents the intermediate host of Schistosoma mansoni in Egypt. Using parasitological and SOD1 enzyme assay, this study aimed to elucidate the impact of the age of B. alexandrina snails on their genetic variability and internal defence against S. mansoni infection. Susceptible and resistant snails were reared individually for self-reproduction; four subgroups of their progeny were used in experiment. The young susceptible subgroup showed the highest infection rate, the shortest pre-patent period, the highest total cercarial production, the highest mortality rate and the lowest SOD1 activity. Among the young and adult susceptible subgroups, 8% and 26% were found to be resistant, indicating the inheritance of resistance alleles from parents. The adult resistant subgroup, however, contained only resistant snails and showed the highest enzyme activity. The complex interaction between snail age, genetic background and internal defence resulted in great variability in compatibility patterns, with the highest significant difference between young susceptible and adult resistant snails. The results demonstrate that resistance alleles function to a greater degree in adults, with higher SOD1 activity and provide potential implications for Biomphalaria control. The identification of the most susceptible snail age enables determination of the best timing for applying molluscicides. Moreover, adult resistant snails could be beneficial in biological snail control.     

Field studies on the bionomics of the free-living stages of St. Lucian Schistosoma mansoni.

Densities of Schistosoma mansoni miracidia and cercariae in natural habitats in three St. Lucian valleys were monitored over a 3-year period by exposure of sentinel snails, Biomphalaria glabrata, and a cercariometric technique, supplemented by sampling of field snails. Separate measures for control of S. mansoni transmission were under evaluation in two of the valleys. Sentinel snails became infected sporadically and their infection rates per valley ranged from 0·12% to 4·99%. S. mansoni miracidial inoculation rates ranged from 1 to over 4 per infected sentinel snail. Combined rainfall of more than 3 in on the day before any day of sentinel snail exposure interfered with miracidium-snail interaction. Densities of S. mansoni cercariae ranged from 0·05 to 21 per litre of water sampled. The number of cercariae detected in a habitat by cercariometry was directly proportional to the number of infected field snails. Sentinel snail infection rates exhibited a downward and an upward trend, respectively, in the controlled and uncontrolled areas, although the changes were not significant statistically.     

Changes in the reproductive biology of Biomphalara glabrata infected with different doses of Echinostoma paraensei miracidia

The egg-laying rate, number of egg masses, number of eggs/mass, number of eggs hatched/snail and egg viability of Biomphalaria glabrata exposed to different doses (5 and 50) of Echinostoma paraensei miracidia were analyzed as indicators of reproductive activity. Polystyrene plates were placed in aquariums containing the snails and every other day for four weeks after infection the plates were removed to count the number of egg masses and eggs laid. After this, the plates were numbered individually and placed in new aquariums free of snails and the egg masses were observed daily to determine the hatching rate. On average there was an increase in the parameters evaluated in the infected snails in relation to the controls (uninfected snails), except for egg viability, which was significantly lower in the groups infected with 50 miracidia. These findings indicate that when infected, this host snail is able to increase its reproductive activity, suggesting an ecological strategy to maintain the species.     

Echinostoma liei miracidia and Biomphalariaglabrata snails: Effect of egg age,habitat heterogeneity,water quality and volume on infectivity

Infectivity of Echinostoma liei miracidia to NIH albino Biomphalaria glabrata declines significantly from 62% with eggs incubated for 10–24 days to 3% for eggs incubated for 30–42 days. In mass exposures of 25 snails to 125 miracidia in 1 liter of water infectivity was high (54–66 %) and not affected by the presence of lettuce, plastic sheets, chalk, detritus or snail-conditioned water. In distilled water or snail-conditioned water the proportion of infected snails exposed singly to five miracidia per snail in 5 ml was not significantly different from the results of mass exposures of 25 snails in 1 liter to the same snail: miracidia ratio. Some evidence is presented suggesting that infected snails are less likely to suffer mortality than uninfected snails during the first 7–10 days post-exposure.The results suggest that Echinostoma liei miracidial searching efficiency is robust in volumes of at least 1 liter and in a heterogeneous habitat. These aspects enhance the competitive potential of echinostomes as possible biological control agents for Schistosoma mansoni.