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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., (© The Author(s) 2019. Published by Oxford University Press on behalf of Royal Society of Tropical Medicine and Hygiene. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

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 Eligible studies included published or unpublished mollusciciding field trials performed before January 2014 involving host snails for S. mansoni or S. haematobium, with a primary focus on the use of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.

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., (Copyright © 2015 Elsevier Inc. All rights reserved.)

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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., (Copyright 2001 John Wiley & Sons, Ltd.)

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.

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.

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.

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 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.

Dried leaf material of a Mexican plant, Agave attenuata, was found to be highly toxic to the target snail, Bulinus africanus, intermediate host of Schistosoma haematobium in South Africa. The molluscicidal potency of the plant underwent seasonal variation, but remained stable over a range of pH values, after exposure to sunlight and organic matter, and during dry storage. It was unstable in aqueous suspension. The toxicity of the molluscicide to crop plants, invertebrates, fish and mammals was lacking or low. Given these properties, A. attenuata may provide a substitute for niclosamide and be used safely for snail control by rural communities.

Hot water extracts of Rheum plamatum and Rheum dentatus (from China) showed molluscicidal activity against the snails Oncomelania hupensis, Biomphalaria glabrata and Bulinus globosus, which are vectors of Schistosoma japonicum, S. mansoni and S. haematobium, respectively. Activity was correlated with antraquinones which were identified by HPLC: rhein and chrysophanol-anthron were most active (> 50% dead snails after 2 days in a 0.03% solution). Molluscicidal activity was intermediate with Rheum-emodin and physcion and was not detectable with cinnamic acid or Aloe-emodin. The snail O. hupensis tended to be more sensitive for several compounds than B. glabrata. Extracts of Jatropha curcas seeds (from Mali) showed molluscicidal activity against both B. glabrata and O. hupensis, the latter being the more sensitive snail. The activity was associated with phorbol esters extracted from Jatropha oil. Of the pure phorbol esters tested, 4 beta-phorbol-13-decanoate killed both snail species at a concentration of 0.001% (10 p.p.m). As Jatropha is locally grown in Mali for other purposes, it might potentially be exploited for schistosomiasis control.

Biomphalaria alexandrina and Bulinus truncatus are the main vectors of human Bilharziasis in Egypt. The mycotic inhabitants of both control and treated snails were surveyed at 7 and 15 days intervals. The two molluscicides affected more on the mortality of Biomphalaria alexandrina than Bulinus truncatus. The highest population of zoosporic fungi was collected from Biomphalaria alexandrina, the lowest from Bulinus truncatus. Copper sulphate was more effective than Bayluscide on the fungal species of both snails. Achlya, Dictyuchus and Saprolegnia were the common genera while Leptolegnia caudata and Pythium ultimum completely missed from treated snails. The total colonies of zoosporic fungi were lowered after. 15 days of treatment. The two molluscicides inhibited the cell division of both tested snails.

A schistosomiasis research project, carried out in Southwest Nigeria, yielded data by which it was possible to relate snail recovery from potential transmission sites to the presence or absence of Tetrapleura tetraptera. A significant negative correlation with snail numbers was found for distance of T. tetraptera from transmission sites and fruiting of the trees when these variables were tested individually. There were no significant differences between individual variables such as pH, Ca2+ concentrations and temperatures for these snail habitats but these variables produced significant positive correlation with the number of snails recovered. Thus, the presence of T. tetraptera appeared to be the most important limiting factor for the presence of snails. Aqueous extracts of T. tetraptera were effective as a molluscicide against Bulinus globosus and Lymnaea natalensis. However, pollution of the environment by oils reduced or abolished the molluscicidal activity of T. tetraptera. The results indicate that the planting of T. tetraptera has potential for the local control of schistosomiasis.

The molluscicidal activity of Gnidia kraussiana Meisn leaf, stem and root was studied. Each morphological part was extracted with cold and boiling water, different organic solvent and successively with organic solvents of increasing polarity. Throughout it was found that the extracts of the root were the most potent followed by the stem. Boiling water extracts were more potent than cold water extracts, while in case of extraction with different organic solvents, the petroleum ether extracts of the root and stem were the most potent, while for the leaf, the ethanolic extract was the most potent. On successive extraction, the petroleum ether extracts of all organs were the most potent. Saponification of the petroleum ether extract of the root was carried out and the activity of the different fractions were tested. Different extract fractions were obtained from the 80 per cent ethanolic percolate of the root. Some of the physical properties and the phytochemical screening of the successive extractives of the three organs were studied.

A preliminary biological screening for molluscicidal activity of certain Sudanese plants used in Folk-medicine was carried out. 78 samples belonging to 51 species, 45 genera and 28 families were screened. The aqueous extracts of 18 samples belonging to 8 species, 6 genera and 5 families were found to be active against Bulinus truncatus and 7 of these were also found to be active against Biomphalaria pfeifferi. Successive extraction of the 18 active samples with petroleum ether, ethanol and water showed that the petroleum ether extracts of only 4 samples were active against Bulinus truncatus; while the alcoholic extracts of 16 samples were found to be active against the same snail species. Only the alcoholic extracts of 4 samples were proved to be active against Biomphalaria pfeifferi. In the successive extraction technique, only the aqueous extract of Gardenia vogelii fruit pulp was proved to be active against the two snail species tested.

Searches for Phytolacca dodecandra were conducted throughout the country in order to determine the natural distribution of the plant molluscicide and to identify the plants that produce the most toxic berries. Berries were collected from a total of 74 plants and bioassays performed against Bulinus globosus. The berries collected from eight plants were found to be lethal to 50% or more of the snails and the most toxic berries were those collected from plants found growing in the drier and hotter parts of the country. The results suggest that the toxicity of the berries depend on the geographical features of the place from which these are collected.

The authors experiment molluscicidal properties of Ambrosia maritima L. from Egypt and cultivated in Senegal. Four generations are tested. Six plants, on eight tested, had same molluscicidal activity as the strain in Egypt.

The effects of the organophosphorous insecticide, Dursban, on aerobic oxidation, glycolysis, glucose utilization and gluconeogenesis in snails tissues were determined. Dursban had a biphasic effect on the aerobic oxidation of succinate, glutamate + malate and TMPD + ascorbate while it had only an inhibitory action on pyruvate oxidation. The compound significantly inhibited glycolysis, glucose utilization and gluconeogenesis when used at high concentrations (ten times higher than its LC50). However, it had a slight effect on thepreviously mentioned process when its concentration was equal to or approximated its LC50. The relationship between the metabolic effect of Dursban and its molluscicidal activity is discussed.

The molluscicidal properties of 5-nitro- and 3-nitro2',4'-dichloro salicylanilides and their mixture 5.5 : 1 were investigated against the intermediate hosts of schistosomes Bulinus truncatus and Biomphalaria alexandrina. Unlike Bayluscide, the activity of the new mulluscicides is not affected by strong sun radiation or by acidic pH. Their activity is resistant to storage, river-bed mud and lower temperature.

Survivors of Bulinus truncatus from one exposure to niclosamide (Bayluscide) were used to establish the next generation in a five generation long laboratory selection for increased tolerance to niclosamide. In a comparison of the tolerance to the molluscicide between two original and two selected strains about 150 snails of each strain, divided into four size-groups, were exposed to aliquots of the same niclosamide solution on the same day and during the same time of the day. It was shown that five generations of relatively mild selection (30-50% survival) resulted in a significant increased tolerance to niclosamide in snails with only one exposure before start of the selection procedure. A comparison with published data indicated that the unselected strains did not change their tolerance to niclosamide during seven years of laboratory breeding. The strain exposed to niclosamide once in each of 16 generations showed an avoidance reaction to the chemical by crawling out of the water.

Although Frescon successfully controlled snails on the margins of the Barombi lakes, and although the continuation of niridazole and Frescon control reduced transmission of S. haematobium very considerably, practical difficulties, which are discussed, rendered the twin goals of snail- and parasite-eradication impossible to achieve. The "break-point" in transmission of S. haematobium appears to lie so low as to be practically synonymous with total eradication. Control operations would thus have had to be maintained indefinitely in order to avoid a rapid return to the pre-control situation. The cost of the control element in this combined chemotherapeutic and molluscicidal research project, at 2 lacustrine foci of S. haematobium transmission in the United Republic of Cameroon, was 9 to 10 U.S. dollars per year per head of population protected. This sum is about three times the country's total estimated expenditure per head of population on all health and social services for the year 1974-1975. The high cost of such operations is only likely to be acceptable where schistosomiasis causes much ill-health and reduced economic productivity, and where tangible benefits may be expected from a reduction in the intensity of infections, short of eradication.

Previous work has shown that the aerobic oxidation of certain intermediates of Krebs cycle by the snail B. alexandrina and B. truncatusis inhibited by TPT. This paper reports data on the effect of TPT on glucose utilization, glycolysis, glycogen content, and glucone ogenesis in snail tissue preparations. The compounds at its LC50 inhibited gluconeogenesis, stimulated glycolysis and markedly reduced the glycogen content and glucose utilization in both snails. However, the effects were more pronounced in B. truncatus than in B. alexandrina. Possible interpretations of these findings are discussed with reference to published arrangements for regulation of gluconeogenesis and glycolysis, coupling of electorn transport to ATP synthesis and also to our present knowledge of the chemical and biological specificity of TPT.

The use of niridazole, in conjunction with snail control, in an attempt to control the transmission of Schistosoma haematobium at 2 Cameroon crater-lake villages is described. Quantitative examinations of urines for S. haematobium eggs were made on the whole population before control began, at intervals during the maintenance of control, and again after control ceased. The methods and difficulties are described, and their accuracy is discussed. After each examination all accessible egg-passers were treated or re-treated with niridazole. The drug was well tolerated and effective. Most treated patients ceased to pass live eggs, and most of those who later became positive again were thought to represent reinfections rather than relapses. During the maintenance of snail control, niridazole treatment of the 'whole' community reduced the total load of S. haematobium eggs passed to less than 1 per cent of the pre-control figure; and repeated subsequent treatments maintained a level of the same order. Despite this, there remained at different times 0.6-50.9 per cent of persons passing small quantities of live eggs, and these were an important source of continuing transmission. The possibility that more than one strain of S. haematobium was involved is discussed. An index of transmission from man to snail is proposed and discussed in relation to determining the level of the "break-point" in transmission. Although combined niridazole/molluscicide control reduced transmission from man to snail by about 3 log cycles, the "break-point", which is thought to lie 4 or more log-cycles lower, was not reached. When control was stopped, transmission built up again, with the prevalence rate in man rising more rapidly than the intensity of infections.

Using a crop-spraying aircraft modified to give a coarse spray, the feasibility of aerial application of the molluscicide N-trityl morpholine to minor canals on the Gezira has been proved. In January 1973, seven canals were sprayed at dosages of 0-1 p.p.m., 0-2 p.p.m., 0-5 p.p.m. and 1-0 p.p.m. Chemical analysis indicated that about 70% of the chemical was present in the water 5-15 hours after the spray, and snail exposure to the sprayed canals indicated that all dosages applied were lethal to Biomphalaria snails. Bulinus snails, which are less susceptible to the molluscicide, were killed only by the 0-5 p.p.m. and 1-0 p.p.m. dosages. Sampling of the natural snail populations of the canals confirmed these results. In March 1973, an area of 464 sq km was treated by drip-feed of 0-1 p.p.m. N-trityl morpholine to kill snails in the main and major canals, and then by aerial spraying 56 of the 58 minor canals in the area. Despite the high winds which disrupted the spray timetable, the canals were successfully treated in 9-5 hours flying-time within seven days. A very high initial snail kill was indicated by both caged snail exposure and natural snail population sampling. However, in excellent snail breeding conditions the area was reinfested with snails within two months. The cost of the application was only 5% of the chemical cost, and aerial spraying in March and May will almost certainly be incorporated in an annual snail control programme.

The effect of butanol extracts of endod against Biomphalaria choanomphala, B. pfeifferi, and Bulinus (Physopsis) nasutus was tested at different concentrations and for different exposure periods. Exposure to 19-25 ppm for 6 hours or to 6-7 ppm for 24 hours caused about 100% mortality.