Biological activity of artemisinin-naphthoquine phosphate on Schistosoma haematobium stages and the vector Bulinus truncatus.

BACKGROUND: Schistosoma haematobium infection is a major public health problem in most of Africa and the Middle East and praziquantel remains the only drug used for schistosomiasis control, therefore emergence of drug resistance is unavoidable. The antimalarial artemisinin-naphthoquine phosphate combination (co-ArNp) was recently documented to have promising effects on Schistosoma mansoni and its snail host. METHODS: We conducted this in vitro study to assess the bioactivity of co-ArNp on S. haematobium and its snail vector Bulinus truncatus. RESULTS: Treatment of S. haematobium worms with 1 µg/ml co-ArNp for 24 h reduced worm motility, while 20 µg/ml resulted in 25-100% mortality of adult flukes within 48-72 h. Incubation of S. haematobium miracidia and cercariae with the molluscicidal co-ArNp (50% lethal concentration 7.5 µg/ml) killed all the free larval stages within 40 and 15 min, respectively. Also, exposure of B. truncatus adult snails to 20 ppm of the combined regimen caused a mortality rate of 100% within 24 h. CONCLUSIONS: Co-ArNp therapy has also shown encouraging activity against the other major human schistosome, S. haematobium, as well as its vector.

Systematic Review and Meta-analysis of the Impact of Chemical-Based Mollusciciding for Control of Schistosoma mansoni and S. haematobium Transmission.

BACKGROUND: Programs for schistosomiasis control are advancing worldwide, with many benefits noted in terms of disease reduction. Yet risk of reinfection and recurrent disease remain, even in areas with high treatment coverage. In the search for means to better prevent new Schistosoma infections, attention has returned to an older strategy for transmission control, i.e., chemical mollusciciding, to suppress intermediate host snail species responsible for S. mansoni and S. haematobium transmission. The objective of this systematic review and meta-analysis was to summarize prior experience in molluscicide-based control of Bulinus and Biomphalaria spp. snails, and estimate its impact on local human Schistosoma infection. METHODOLOGY/PRINCIPAL FINDINGS: The review was registered at inception with PROSPERO (CRD42013006869). Studies were identified by online database searches and hand searches of private archives. Eligible studies included published or unpublished mollusciciding field trials performed before January 2014 involving host snails for S. mansoni or S. haematobium, with a primary focus on the use of niclosamide. Among 63 included papers, there was large variability in terms of molluscicide dosing, and treatment intervals varied from 3-52 weeks depending on location, water source, and type of application. Among 35 studies reporting on prevalence, random effects meta-analysis indicated that, on average, odds of infection were reduced 77% (OR 0.23, CI95% 0.17, 0.31) during the course of mollusciciding, with increased impact if combined with drug therapy, and progressively greater impact over time. In 17 studies reporting local incidence, risk of new infection was reduced 64% (RR 0.36 CI95% 0.25, 0.5), but additional drug treatment did not appear to influence incidence effects. CONCLUSION/SIGNIFICANCE: While there are hurdles to implementing molluscicide control, its impact on local transmission is typically strong, albeit incomplete. Based on past experience, regular focal mollusciciding is likely to contribute significantly to the move toward elimination of schistosomiasis in high risk areas.

RETRACTED: Glyphosate herbicide induces genotoxic effect and physiological disturbances in Bulinus truncatus snails.

Herbicides are being used in agriculture for controlling noxious weed. Glyphosate is a herbicide that is widely applied to cereal crops in Egypt and is used in controlling a very broad spectrum of weeds. The present study was designed to investigate the response of the snail Bulinus truncatus as a bioindicator for physiological and molecular aspects of B. truncatus snails after exposure to sublethal concentrations of glyphosate for two weeks. In treating snails, glucose concentration (GL) in the haemolymph as well as lactate (LT) in soft tissues of treated snails increased, while glycogen (GN), pyruvate (PV), total protein (TP), nucleic acids (DNA and RNA) levels in snail's tissues decreased. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR), thioredoxin reductase (TrxR), glycogen phosphorylase (GP), glucose-6-phosphatase (G-6-Pase), succinic dehydrogenase (SDH) and lactic dehydrogenase (LDH) enzymes in homogenate of snail's tissues were reduced in response to the treatment with the herbicide, while lipid peroxide (LP), sorbitol dehydrogenase (SDH) and transaminases (GOT and GPT) activity increased (P < 0.001). The changes in the number, position and intensity of DNA bands induced by glyphosate herbicide may be attributed to the fact that the herbicide can induce genotoxicity through DNA damage. Thus, the present result indicated that the genotoxicity products at low concentration and for long time treatment showed the hazard of herbicide addiction on man's life.

Age-dependent susceptibilities of Bulinus truncatus snails to an aqueous extract of Pulicaria crispa (Forssk.) Oliv. (Asteraceae) leaves.

This study was carried out to investigate the potential use of the herb Pulicaria crispa in the biological control of different developmental stages of Bulinus truncatus, a major snail intermediate host of urinary schistosomiasis. Age-dependent susceptibilities of mature adult snails, immature snails, juveniles, and one-day old egg masses to aqueous extracts of Pulicaria crispa leaves collected from Khartoum (Sudan) and Riyadh (Saudi Arabia) was determined and compared. The results show the juvenile snails are the most susceptible, followed in descending order by one-day old egg masses, immature snails, and mature adult snails. The P. crispa sample collected from Riyadh was significantly more potent against B. truncatus than that collected from Khartoum, as indicated by the least (LC50) and (LC90) values for all B. truncatus ages.

Molluscicidal and schistosomicidal activities of a steroidal saponin containing fraction from Dracaena fragrans (L.).

The steroidal saponin-containing fraction from methanolic extract of Dracaena fragrans (Family: Agavaceae) was tested for molluscicidal and ovicidal activities against Biomphalaria alexandrina and Bulinus truncatus, the snail vectors of Schistosoma mansoni and S. haematobium in Egypt, respectively. It was also tested for schistosemicidal activity in vitro on adult S. mansoni and against the free-living miracidia and cercariae of the parasite. The homogenated soft body of B. alexandrina was used to determine the effect of the saponin fraction on total protein, albumen, aminotransferase enzymes and acetylcholin esterase. The results showed that the saponin fraction had considerable molluscicidal activity; LC50 & LC90 were 2.7 ppm & 3.7 ppm for B. alexandrina and 2 ppm & 2.5 ppm for B. truncatus, respectively. Snail eggs did not hatch in concentration as low as half molluscicidal LC50 (1.35 ppm). The LC50 killed all miracidia and cercariae in 30 seconds and after 22 & 40 minutes at a very low concentration (0.165 ppm) respectively, and had in vitro lethal effect on adults with LC50 18.4 microg/ml 4 days post-exposure. The snail tissue homogenate showed significant increase in total protein content & albumen, in aminotransferases and acetylcholinesterase activities.

Electrophoretic patterns of protein fractionations in hemolymph and tissues of Biomphalaria alexandrina and Bulinus truncatus during course of schistosome infection.

Electrophoresis of plasma protein of B. alexandrina (uninfected & infected with S. mansoni) showed that the major dominant bands had molecular weights of 20, 44, 96, 139 & 205 KD in both types of snails. The 1day & 1 week post miracidial exposure (PME) groups were characterized by band 54 KD. All groups except a day PME were characterized by a common band of MW 65 KD. Three days PME group had. three bands of 123 KD, 150 &177 KD, not found in other groups. The highest similarity index in 2 weeks PME & 5 weeks PME groups (during cercarial shedding) was 0.667 and the lowest one was in 3-days PME (0.5). The 3-days PME had a unique band of MW 177.04 KD, not found in other groups. Similar electrophoretic pattern of B. alexandrina tissue protein was seen. The major dominant bands had molecular weights of 14, 21, 80 and 140 KD in both non-infected and infected snails. The 1day PME had a band of 48.483 KD, 3-days PME had a band of 87.985 KD, one-week PME group characterized by two bands 61.761 KD and 70.338 KD. The two-weeks PME had a band 91.111 KD. While, the 5 week PME (during cercarial production) was the only group that shared the common band of MW 115 KD with controls. The highest similarity index in 5 weeks PME (during cercarial shedding) group was 0.545 and the lowest one was in 1 week & 2 weeks PME (0.43). The electrophoresis of plasma protein of B. truncatus (uninfected & infected with S. haematobium) showed that the major dominant bands had molecular weights of 20, 30, 65, 80, 106, 117 & 170 KD in both type of snails. The 1day PME group was characterized by three bands of MWs 26.539, 51.891 & 91.509 KD. All experimental groups, except 5 weeks PME (during cercarial shedding) and control, had a common band of MW 45 KD. Three days PME group had a characteristic band of 113.72 KD which was not found in any other group. The highest similarity index was in one week PME group was 0.857 and the lowest one in 1-day PME (0.5). In B. truncatus tissue protein, the major dominant bands by electrophoretic pattern had molecular weights of 20, 45, 54, 80, 97 & 171 KD in both type of snails. A day PME had a band of 73.544 KD and a week PME had a band of MW 60.813 KD. Two and 5 weeks PME groups had 2 bands of MWs 27 & 62 KD. All experimental groups had a characteristic band not found in control of MW 141 KD. The highest similarity index in 3-days PME was 0.8 and the lowest one was in 5 weeks PME during cercarial shedding(0.545).

Field trials of low dose Bayluscide on snail hosts of schistosome and selected non-target organisms in sahelian Cameroon.

More than 85% of all cases of schistosomiasis in Cameroon occur in the northern sahelian half of the country representing 20% of the population. Several workers have advocated the integrated approach to schistosomiasis control, including snail control, but the death and decay of aquatic organisms, and fish kill that often follows Bayluscide application at the dose of 1 g/m3 decrease its acceptability. The present study was designed to assess the effect of lower Bayluscide doses on snail host and non-target fish, frog, the tadpole kill. Bayluscide was applied to study ponds at concentrations of 0, 0.25, 0.5, and 1 g/m3 (ppm). Pre and post application assessment of snails hosts of schistosomes, fish, frog, and tadpole kill were carried out. All 0.25, 0.5, and 1 g/m3 Bayluscide concentrations reduced snail population significantly. Bayluscide concentration of 0.50 g/m3 applied in two rounds of 0.25 g/m3 resulted in high snail mortality and low lethality to fish, frogs, and tadpoles. Further studies are needed to assess the cost-effectiveness of Bayluscide in the control of schistosomiasis following the simplified approach.

Molluscicidal activities of aqueous extract of the sea anemone Parasicyonis actinostoloides against vector snails Bulinus truncatus and Lymnaea natalensis.

The aqueous extract of the sea anemone Parasicyonis actinostoloides showed molluscicidal effect against vector snails of Schistosoma hacematobium and Fasciola gigantica after 24 hours of exposure. LC50) and LC90 values for P. actinostoloides were 40 & 78.6 ppm for B. runcatus and 46.6 & 86.5 ppm for L. natalensis respectively. The effect of continuously exposure of B. truncatits and L. naltlensis to sublethal aqueous extract concentrations (LC0, LC10 & LC25) on survival rate, egg production and on infectivity of miracidia to infection with S. haematobium and F. gigantica were studied. The data showed that no B. truncatus survived more than 42, 32 & 27 days after exposure with a mean life span of 18.5, 13.3 & 11.1 days respectively. The death rate of B. truncatus with LC0 was highly significant as compared to treatment with LC10 & LC25 (p < 0.01). L. natalensis were more susceptible to the effect of aqueous extract than B. truncatus. LC0, LC10 & LC25, extract killed all L. natalensis through 32, 27 & 22 days. The mean life span of those exposed to LC0 was 12.37 days, high significant when compared with treated LC10 & LC25 ones (p < 0.01). The cumulative mortality rates of B. truncatus and L. natalensis in controls during the experimental study (52 days) was 60% & 75%, respectively. Egg production of B. truncatius and L. natalensis was not affected by sublethal concentrations. Control snails layed significantly higher no. of eggs than treated ones. B. truncatus stopped egg laying 17 days after exposure to LC25. those treated with LC10 & LC0 ceased to deposit eggs after 22 & 27 days respectively. The percent reduction in egg laying capacity of B. truncatus treated with LC0, LC10 & LC25 compared to controls was 77.1%, 93.2% & 92.8% respectively (p < 0.01). Similar reduction in egg production of treated L. natalensis cornpared to controls occurred, the percent reduction in egg production of snails treated with LC0, LC10 & LC25 in relation to controls was 78.4%, 92.4% & 94.7% respectively. Sublethal concentrations of aqueous extract of P. actinostoloides affected hatchability of B. truncatus and L. natalensis eggs. The data showed that eggs of B. truncatus and L. natalensis can hatch in all tested concentrations but with different rates. The eggs' hatchability in snails exposed to LC0, LCIo & LC25 extract at 5 days old was 44%, 38% & 30% in B. truncatus respectively. In L. natalensis eggs, the corresponding rates were lower 28%, 24% & 18% respectively. The infection of B. truncatuts and L. natalensis with S. haematobium n and F. giganlica miracidia was greatly reduced by the sublethal concentrations of aqueous extract of P. actinostoloides. The reduction of infection rate increased with the increased of sublethal concentrations. In B. truncatus the reduction was 43.2%, 57.6% & 76.6% compared to controls and in L. natalensis was 56.3%, 70.2% & 77.4%, respectively.

Molluscicidal activity against Bulinus truncatus of Croton campestris.

The bark of Croton campestris provided three furano-clerodane named, respectively, velamone, velamolone acetate and velamolone. Fractions containing these diterpenoids were investigated for their molluscicidal activity against Bulinus truncatus, one of the aquatic snail vectors of schistosomiasis. A dichloromethanic extract of root barks, rich in furano-clerodane and molluscicidal at 20ppm was promising as natural molluscicide. Enriched fraction with velamone gave 80% mortality from 25ppm, while its LD(100) was at 50ppm. The LD(80) was ca. at 45ppm, while LD(100) was at 60ppm for the enriched fraction containing velamolone acetate. The velamolone-enriched fraction was less efficient and gave a mortality of 90% at 90ppm. The pure compounds, velamone and velamolone acetate were active at 100% at 3 and 6ppm, respectively. Velamolone showed a molluscicidal activity at 20ppm.

Molluscicidal activity of some Cameroonian plants on Bulinus species.

OBJECTIVE: To evaluate some locally available plants for their molluscicidal activity on Bulinus camerunensis and B. truncatus (slender form). DESIGN: Experimental studies. SETTING: Ndongo stream near the University of Buea and the University of Buea Life Sciences Laboratory. SUBJECTS: Evaluation of molluscicidal activity on snails of Bulinus camerunensis and B. truncatus (slender form). MAIN OUTCOME MEASURES: Plant extracts with molluscicidal activity determined. Determination of LC50, LC90 and LC100 of the potent plant extracts. Application of the extracts on aquaria-reared snails. Semi-field application of extracts. RESULTS: A preliminary screening test using 10,000 ppm solution of the water extracts of thirteen plants revealed that 61.5% (8/13) of the plants investigated had molluscicidal properties, with snail mortality rates above 90%. Extracts of Nicotiana tabacum, Aframomum citratum, A. melegueta, Curcuma domestica and Solanum scabrum killed 100% of the snails after twenty four hours exposure. B. camerunensis was more susceptible to the water extracts than B. truncatus. The LC50, LC90 and LC100 of the different plant extracts against B. camerunensis were generally lower than those against B. truncatus. The concentrations that produced 50%, 90% and 100% snail mortalities were lower with the methanol extracts than with water extracts, indicating that the methanol extracts were more toxic. to the snails than the water extracts. Generally, the eggs were more susceptible to the extracts than the young and adult snails. Application of the water extracts at LC 100 on snails reared in aquaria and under semi-field conditions revealed that N. tabacum could kill up to 100% of the snails in aquaria and 61.25% under semi-field conditions. CONCLUSION: Eight plant species with molluscicidal activity were identified, among which Nicotiana tabacum, Aframomum citratum, A. melegueta, Solanum scabrum and Curcuma domestica presented the highest activity. B. camerunensis was more susceptible to all the plant extracts tested than B. truncatus, and the methanol extracts proved more toxic than the water extracts. Semi-field testing of potent extracts showed promise, with N. tabacum having the highest effects on the snails.

Field trials of low dose Bayluscide on snail hosts of schistosome and selected non-target organisms in sahelian Cameroon

More than 85 percent of all cases of schistosomiasis in Cameroon occur in the northern sahelian half of the country representing 20 percent of the population. Several workers have advocated the integrated approach to schistosomiasis control, including snail control, but the death and decay of aquatic organisms, and fish kill that often follows Bayluscide application at the dose of 1g/m³ decrease its acceptability. The present study was designed to assess the effect of lower Bayluscide doses on snail host and non-target fish, frog, the tadpole kill. Bayluscide was applied to study ponds at concentrations of 0, 0.25, 0.5, and 1 g/m³ (ppm). Pre and post application assessment of snails hosts of schistosomes, fish, frog, and tadpole kill were carried out. All 0.25, 0.5, and 1 g/m³ Bayluscide concentrations reduced snail population significantly. Bayluscide concentration of 0.50 g/m³ applied in two rounds of 0.25 g/m³ resulted in high snail mortality and low lethality to fish, frogs, and tadpoles. Further studies are needed to assess the cost-effectiveness of Bayluscide in the control of schistosomiasis following the simplified approach.

The relative susceptibilities of juvenile and adult Bulinus globosus and Bulinus truncatus to the molluscicidal activities in the fruit of Ghanaian Blighia sapida, Blighia unijugata and Balanites aegyptiaca.

The relative susceptibilities of juvenile (2- to 3-week-old) and adult (5- to 7-week-old) Bulinus globosus and Bu. truncatus to the molluscicidal activities of aqueous preparations of the powdered, dried fruits of Blighia sapida, Bl. unijugata and Balanites aegyptiaca were investigated under laboratory conditions. For the extract prepared from the freeze-dried, semi-ripe fruits of Bl. sapida, the concentrations killing 95% of the snails after an exposure for 24 h (LC95) were, respectively, 232.7 and 161.2 ppm for the juveniles and adults of Bu. globosus and 187.6 and 140.2 ppm for the juveniles and adults of Bu. truncatus. The corresponding values for Bl. unijugata were 136.9 and 98.7 ppm for Bu. globosus and 132.2 and 98.5 ppm for Bu. truncatus, respectively. Extracts of the freeze-dried, ripe fruit of Ba. aegyptiaca were much more active, however, giving LC95 of just 16.9 and 19.7 ppm for the juveniles and adults of Bu. globosus, and 14.2 and 12.0 ppm for the juveniles and adults of Bu. truncatus, respectively. In general, similar results were obtained when the fruit were oven-dried rather than freeze-dried but the potency of Balanites extracts produced from oven-dried fruit was relatively low. That the juvenile snails appeared less susceptible than the adults to the molluscicidal activity in each Blighia extract is interesting. This observation may have implications for snail control, in terms of the optimal frequency, timing and concentration of molluscicides applied in a particular habitat.

The effects of myrrh (Commiphora molmol) on the infected snails of Schistosoma sp. and their egg masses: effect on shedding of cercariae and on snail fecundity.

Myrrh has molluscicidal effect on infected Bulinus truncatus and Biomphalaria alexandrina snails at low concentrations (10 & 20 ppm respectively) after 24 hours exposure. The number of dead-snails increased with prolongation of exposure time. All Schistosoma free cercariae were killed by 2.5 ppm within 15 minutes. One day-old egg masses were more susceptible to the ovicidal effect of Myrrh than the five-day old ones. Both types of eggs were more resistant to the effect of Myrrh than the adult snails, embryogenesis began to stop at 20 ppm and eggs were all killed at 60 & 80 ppm. Shedding of cercariae of Schistosoma mansoni from infected B. alexandrina stopped at 1 ppm and was suppressed at 0.8 ppm. Snail fecundity decreased at 1 ppm.

Screening of Malian medicinal plants for antifungal, larvicidal, molluscicidal, antioxidant and radical scavenging activities.

A total of 78 different extracts from 20 medicinal plants belonging to 14 plant families from Mali were tested for their antifungal, larvicidal, molluscicidal, antioxidant and radical scavenging activities. Dichloromethane, methanol, water and ethanol extracts were used. TLC autobiography for antifungal activity was run with Cladosporium cucumerinum and Candida albicans. Extracts were also tested on the larvae of the mosquitoes Aedes aegypti, Anopheles gambiae and Culex quinquefasciatus. Molluscicidal activities were established with the snails Biomphalaria glabrata, Biomphalaria pfeifferi and Bulinus truncatus. beta-Carotene and DPPH solutions sprayed on TLC plates were used for antioxidant and radical scavenging assays. Of the extracts investigated, 20% were antioxidant and radical scavengers, 19% fungicidal, 30% were larvicidal and 11% were molluscicidal. Three of the plant extracts, from Cussonia barteri (Araliaceae), Glinus oppositifolius (Aïzoaceae) and Lannea velutina (Anacardiaceae) gave positive responses in all four tests.

Laboratory assessment of the molluscicidal activity of Commiphora molmol (Myrrh) on Biomphalaria alexandrina, Bulinus truncatus and Lymnaea cailliaudi.

The molluscicidal properties of the oil extract of Commiphora molmol (Myrrh) were tested against Egyptian snail species: Biomphalaria alexandrina, Bulinus truncatus and Limnaea cailliaudi. The impact of the extract on the egg cluches of B. alexandrina and L. cailliaudi was also evaluated. Snails and their eggs were exposed for 24 and 48 hr at 22-26 degrees C to various concentrations of the extract. The results showed different susceptibilities B. alexandrina showed higher LD50 and LD90 (155, 195 ppm) than B. truncatus (50, 95 ppm) and L. cailliaudi (50, 85 ppm) after 24 hr exposure. 100% mortality was obtained for the egg cluches of B. alexandrina and L. cailliaudi at concentrations of 100 ppm and 75 ppm respectively. Lower concentrations were needed to obtain the same results after 48 hr. The present laboratory studies demonstrated that Myrrh has a molluscicidal effect on the snail intermediate hosts, particularly on their eggs. Field studies are recommended.

Antibacterial and molluscicidal activities of the essential oil of Chrysanthemum viscidehirtum.

The volatile fraction of Chrysanthemum viscidehirtum aerial parts, consisting mainly of limonene, beta-farnesene and many oxygenated sesquiterpenes, was screened for activity against 21 microbial strains. This essential oil exhibited activity against all germs tested, in particular Salmonella typhi and Proteus mirabilis. It also showed molluscicidal activity against Bulinus truncatus.

The molluscicidal properties of Apodytes dimidiata (Icacinaceae): geographical variation in molluscicidal potency.

Synthetic molluscicides have proved too expensive for most countries wanting to include snail control in their anti-schistosomiasis programmes. An alternative, which is not only cheaper but also promotes self-reliance and empowerment of the affected communities, is the use of molluscicidal plants. An often-cited limitation to using such natural products is the geographical variation in the toxicity of candidate species. The geographical variation in the molluscicidal activity of Apodytes dimidiata was investigated in South Africa. Leaves of this plant were collected from six, widely separate localities within the areas of the country where schistosomiasis is endemic. The results of bio-assays using the intermediate host snail, Bulinus africanus, clearly showed that variation in toxicity did exist and appeared to be correlated with the range in mean annual temperatures and altitude where the plants grew. Whether the variation was a phenoplastic response to the environment or genetically determined still has to be investigated. Nevertheless, a thorough knowledge of the geographical variation in the level of the active compound(s) in the candidate plants in endemic areas will be needed prior to the implementation of plant-propagation and snail-control programmes.

Gross histopathological effects of an extract of Agave attenuata on the epithelium of the digestive tract of Bulinus africanus.

A lethal concentration of a crude, aqueous extract of Agave attenuata was applied as a contact poison to Bulinus africanus, the intermediate host of Schistosoma haematobium, for a 24-h period. The gross histopathological effects of the extract on the epithelium of the digestive tract were then studied. A graded series of cellular injuries to the epithelial layer was observed along the length of the tract. These included the loss of cilia and brush border, disruption of the epithelial layer, cellular vacuolation, swelling and rupture, and the discharge of secretory products from mucous gland cells. The results of the microscopy show that epithelial tissue is probably a primary target of the molluscicide. The cytological injuries induced by extracts of A. attenuata indicate that the molluscicide acts by disrupting the osmoregulatory mechanisms of the epithelial cells, but further, detailed studies are required to confirm this.

Evaluation of three methods to control Bulinus truncatus, the intermediate host of Schistosoma haematobium in an irrigation scheme, Tessaout-Amont, Morocco.

In Morocco, the implementation of new irrigation schemes resulted in the introduction of schistosomiasis haematobium to new areas. Canal structures (especially syphon boxes) were found to be favourable habitats for Bulinus truncatus and they constitute important transmission sites. Three methods for snail control in these syphon boxes were assessed in the Tessaout-Amont irrigation scheme. Molluscicide (niclosamide) application resulted in a pronounced reduction in the snail population density, but snails started to recolonise the sites a few months later. Regular brushing of the inner sides of the syphon boxes and covering the syphon boxes, so as to exclude light, resulted in significant reductions in snail numbers. However, the latter methods were not as efficient as the molluscicide.

The molluscicidal activity of Crown of Christ (Euphorbia splendens var. hislopii) latex on snails acting as intermediate hosts of Schistosoma mansoni and Schistosoma haematobium.

The present study describes the action of the latex of Euphorbia splendens var. hislopii (E. milli) on species of the genus Bulinus and on Biomphalaria pfeifferi, intermediate hosts of schistosomiasis in Africa, and the Brazilian snails B. glabrata, B. tenagophila, and B. straminea, intermediate hosts of schistosomiasis in Brazil. The impact of the latex on the egg masses and embryos of B. glabrata was also evaluated. Using the standardized methodology of the World Health Organization for testing plant-derived molluscicides, we obtained a 90% lethal dose (LD90) ranging from 0.13 ppm for B. glabrata subjected to lyophilized latex to 4.0 ppm for B. pfeifferi tested with the natural latex. This material has proved to be one of the most potent and specific plant molluscicides discovered thus far, presenting advantages in terms of application so that it could be used in programs involving community participation in endemic areas in both Brazil and Africa.