Species Of Bulinus Research Articles

Species diversity and distribution of schistosome intermediate snail hosts in The Gambia.

There is a need for recent information on intermediate snail hosts of schistosomes in The Gambia; the previous studies were conducted over three decades ago. This study assessed the incidence, species diversity, distribution and infection status of schistosome intermediate snail hosts in the country. Malacological surveys were conducted in all 5 regions of The Gambia: Central River Region (CRR), Upper River Region (URR), Western Region (WR), Lower River Region (LRR) and North Bank Region (NBR). Sampling of snails was undertaken at 114 sites that included permanent water bodies such as streams (bolongs), rice fields, irrigation canals and swamps; and temporal (seasonal) laterite pools. Ecological and physicochemical factors of sites were recorded. Snails were identified morphologically and screened for schistosome infections using molecular techniques. Freshwater snails were found at more than 50% (60/114) of sites sampled. While three species of Bulinus were collected, no Biomphalaria snails were found in any of the sites sampled. Of the total 2877 Bulinus snails collected, 75.9% were identified as Bulinus senegalensis, 20.9% as Bulinus forskalii and 3.2% as Bulinus truncatus. Seasonal pools produced the largest number of snails, and CRR was the region with the largest number of snails. Bulinus senegalensis was found more in seasonal pools as opposed to permanent sites, where B. forskalii and B. truncatus were observed to thrive. Bulinus snails were more common in seasonal sites where aquatic vegetation was present. In permanent sites, the abundance of snails increased with increase in water temperature and decrease in water pH. Bulinus senegalensis was found infected with both S. haematobium and S. bovis, while B. forskalii and B. truncatus had only S. bovis infection. While the human parasite S. haematobium was restricted to just four sites, the livestock parasite S. bovis had a much more widespread geographical distribution across both CRR and URR. This new information on the distribution of intermediate snail hosts of schistosomes in The Gambia will be vital for the national schistosomiasis control initiative.

Mitochondrial genome of Bulinus truncatus (Gastropoda: Lymnaeoidea): Implications for snail systematics and schistosome epidemiology

Many freshwater snails of the genus Bulinus act as intermediate hosts in the life-cycles of schistosomes in Africa and adjacent regions. Currently, 37 species of Bulinus representing four groups are recognised. The mitochondrial cytochrome c oxidase subunit 1 (cox1) gene has shown utility for identifying and differentiating Bulinus species and groups, but taxonomic relationships based on genetic data are not entirely consistent with those inferred using morphological and biological features. To underpin future systematic studies of members of the genus, we characterised here the mitochondrial genome of Bulinus truncatus (from a defined laboratory strain) using a combined second- and third-generation sequencing and informatics approach, enabling taxonomic comparisons with other planorbid snails for which mitochondrial (mt) genomes were available. Analyses showed consistency in gene order and length among mitochondrial genomes of representative planorbid snails, with the lowest and highest nucleotide diversities being in the cytochrome c oxidase and nicotinamide dehydrogenase subunit genes, respectively. This first mt genome for a representative of the genus Bulinus should provide a useful resource for future investigations of the systematics, population genetics, epidemiology and/or ecology of Bulinus and related snails. The sequencing and informatic workflow employed here should find broad applicability to a range of other snail intermediate hosts of parasitic trematodes.

Efficacy of praziquantel and reinfection patterns in single and mixed infection foci for intestinal and urogenital schistosomiasis in Cameroon

The regular administration of the anthelminthic drug praziquantel (PZQ) to school-aged children (and other high-risk groups) is the cornerstone of schistosomiasis control. Whilst the performance of PZQ against single schistosome species infections is well-known, performance against mixed species infections is less so, as are patterns of re-infection following treatment. To address this, a study using a double treatment with PZQ, administered at 40mg/kg spaced by 3 weeks, took place in two mixed intestinal-urogenital schistosomiasis foci in northern Cameroon (Bessoum and Ouro-Doukoudje) and in one single intestinal schistosomiasis infection focus (Makenene). A total of just under 1000 children were examined and the Schistosoma-infected children were re-examined at several parasitological follow-ups over a 1-year period posttreatment. Overall cure rates against Schistosoma spp. in the three settings were good, 83.3% (95% confidence interval (CI)=77.9–87.7%) in Bessoum, 89.0% (95% CI=79.1–94.6%) in Ouro Doukoudje, and 95.3% (95% CI=89.5–98.0%) in Makenene. Interestingly, no case of mixed schistosome infection was found after treatment. Cure rates for S. mansoni varied from 99.5% to 100%, while that for S. haematobium were considerably lower, varying from 82.7% to 88.0%. Across transmission settings, patterns of re-infection for each schistosome species were different such that generalizations across foci were difficult. For example, at the 6-month follow-up, re-infection rates were higher for S. haematobium than for S. mansoni with re-infection rates for S. haematobium varying from 9.5% to 66.7%, while for S. mansoni, lower rates were observed, ranging between nil and 24.5%. At the 12-month follow-up, re-infection rates varied from 9.1% to 66.7% for S. haematobium and from nil to 27.6% for S. mansoni. Alongside these parasitological studies, concurrent malacological surveys took place to monitor the presence of intermediate host snails of schistosomiasis. In the two northern settings, three species of Bulinus (intermediate host snail of S. haematobium) were collected; i.e. Bulinus truncatus, B. globosus and B. senegalensis, however, Biomphalaria pfeifferi (intermediate host snail of S. mansoni) was much rarer despite repeated and intensive searching and was suggestive of limited local transmission potential of S. mansoni during this time. While this study highlights that performance of PZQ was satisfactory in this region, with somewhat greater impact upon intestinal than urogenital schistosomiasis, the dynamics of local transmission are shown, however, to be complex.

Parasitological and malacological surveys reveal urogenital schistosomiasis on Mafia Island, Tanzania to be an imported infection

To confirm the local endemicity of Schistosoma haematobium on Mafia Island, Tanzania, conjoint parasitological and malacological surveys were undertaken in July 2006 with parasitological investigations supplemented with case-history questionnaires. A total of 238 children (125 girls and 113 boys, mean age of 13.9 years) across 9 primary schools were examined. The prevalence of micro-haematuria and egg-patent infection was 18.1% (CI95=9.6–33.6) and 4.2% (CI95=1.9–7.6), respectively but a strong female bias was observed for micro-haematuria (5.6F:1M) contrasting with a strong male bias for the presence of eggs (1F:4M). All egg-patent infections were of light-intensity (<10eggs/10ml). No clear associations between infection prevalence and local water-contact, by school, were found and all 10 of the egg-positive children had a travel history to the nearby mainland or Zanzibar. Inspection of community diagnostic registers at Kilindoni Hospital revealed a low proportion (<2%) of egg-patent infection for 20,306 samples tested in the 2000–2005 period. A total of 43 freshwater sites, a third of which were previously sampled in 1999 and 2002, were surveyed and 11 species of freshwater mollusc were found. Four species of Bulinus (B. nasutus, B. forskalii, B. barthi and B. sp.) were encountered across 13 sites with B. nasutus restricted to 3 of these towards the north of the island. No collected snail was observed to shed schistosome cercariae. Further characterisation of B. nasutus and S. haematobium included infection challenge on two occasions, with miracidia obtained from egg-patent children from Mafia and Unguja islands as well as DNA barcoding of snails and schistosomes. B. nasutus was shown refractory to infection. With the substantial travel to and from Mafia, the refractory nature of local snails and evidence from DNA barcoding in schistosomes and snails, we conclude that urogential schistosomiasis is an imported infection.

A molecular phylogenetic analysis of Bulinus (Gastropoda: Planorbidae) with conserved nuclear genes

Jørgensen, A., Madsen, H., Nalugwa, A., Nyakaana, S., Rollinson, D., Stothard, J. R. &amp; Kristensen, T. K. A molecular phylogenetic analysis of Bulinus (Gastropoda: Planorbidae) with conserved nuclear genes. —Zoologica Scripta, 40, 126–136.Mutational saturation of inspected DNA loci and topological incongruence in the phylogenetic inferences have previously confounded attempts to resolve the evolutionary relationships within the freshwater snail genus Bulinus. Traditionally, the 37 species of Bulinus are placed within the four species groups and the evolutionary divergence between groups is substantial. With an intention to shed new light on species group relationships, the present study was designed to investigate the basal divergences in the phylogeny of Bulinus using highly conserved nuclear genes. The resolved phylogeny inferred that the four species groups of Bulinus were monophyletic and Shimodaira‐Hasegawa topology tests found them to be significantly supported. The Bulinus truncatus/tropicus species complex and Bulinus wrighti (Bulinus reticulatus group) formed a well‐supported sister‐group relationship. The Bulinus africanus species group was the sister‐group to the clade (Bulinus truncatus/tropicus + B. wrighti) with the Bulinus forskalii species group as the sister‐group to these taxa. The sister‐group relationship between Indoplanorbis and Bulinus was non‐significant and the basal clade support of Bulinus improved upon exclusion of Indoplanorbis. The finding of basal long branches of Bulinus species originating from Madagascar strongly suggests the presence of additional cryptic species and an evolutionary scenario influenced by this island’s geological vicariance from the African mainland. Speciation by polyploidy was inferred to have evolved within a clade in the Bulinus truncatus/tropicus species complex. Although the monophyletic status of each species group was firmly supported, it was difficult to establish species group concepts equally across the variations and place this precisely in a specific temporal framework.

Genetic diversity of schistosomes and snails: implications for control

Molecular approaches are providing new insights into the genetic diversity of schistosomes and their intermediate snail hosts. For instance, molecular tools based on the polymerase chain reaction are being developed for the diagnosis of schistosomiasis and the detection of prepatent schistosome infections in snails at transmission sites. Robust phylogenies of the different species of Schistosoma, Bulinus and Biomphalaria have been determined and novel methods are available to identify the different and cryptic taxa involved. Microsatellite analyses and mitochondrial DNA sequencing methods have been developed and are contributing to a better understanding of the genetic structure of both schistosome and snail populations. New sampling procedures to capture DNA of eggs and larval stages of schistosomes in field situations are facilitating more detailed and ethically advantageous studies on parasite heterogeneity. Knowledge of the genetic diversity of schistosome and snail populations adds a further dimension to the monitoring and surveillance of disease, and the implementation of new molecular-based approaches will be of increasing importance in helping to assess the impact of schistosomiasis control strategies.

Microsatellites in the freshwater snail Bulinus globosus (Gastropoda: Planorbidae) from Zanzibar

AbstractSix microsatellite loci were isolated and characterized in Bulinus globosus, a freshwater snail with a wide distribution throughout sub‐Saharan Africa. Bulinus globosus is an intermediate host of Schistosoma haematobium, the causative agent of human urinary schistosomiasis. Microsatellites were tested using 32 snails from four populations collected from Pemba and Unguja islands of Zanzibar. The microsatellite loci displayed relatively low levels of variation, with between two and five alleles per locus. FST estimates indicate that gene flow is low, as has previously been suggested for other species of Bulinus.

Freshwater snails on Mafia Island, Tanzania with special emphasis upon the genus Bulinus (Gastropoda: Planorbidae)

AbstractA survey of freshwater snails on Mafia Island has been conducted that mapped the distribution and, by using a timed searching strategy, documented the relative levels of abundance of species. Twenty‐five freshwater habitats around the island were surveyed; snails were found in 15 sites (60%). From the total number of snails collected (n=240), prosobranchs (59%) outnumbered pulmonates (41%). Potential intermediate hosts of urinary schistosomiasis were encountered and these Bulinus species were further characterized by analysis of six enzyme systems (GPI, PGM, MDH, HBDH, GDH &amp; AcP), by inspection of DNA sequence variation within mitochondrial cytochrome oxidase sub‐unit I (COI) and nuclear ribosomal internal transcribed spacer (ITS). Three species of Bulinus were found: a single B. africanus group taxon, B. nasutus, and two B. forskalii group taxa, B. forskalii and a species presently identified as Bulinus sp. in this paper. The genera Pila, Lanistes and Bulinus were widespread across the island and dominated the fauna. The remaining taxa were found in lower numbers and often only at single sites. Three prosobranchs: Lanistes purpureus, Pila ovata and Melanoides tuberculata were found. In addition to Bulinus, the pulmonates included a small discoidal planorbid (?)Ceratophallus and an ancylid (a freshwater limpet). The factors that shape the dispersal and distribution of molluscs on Mafia were considered. Water chemistry could be an important variable as both pH (mean 6.37±0.99 SD) and conductivity (mean μS=149±135 SD) were significantly different from similar habitats on neighbouring Zanzibar Island (P&lt;0.001). The Mafian fauna is clearly associated with that of mainland Africa and Madagascar.

Bulinus species on Madagascar: molecular evolution, genetic markers and compatibility with Schistosoma haematobium.

Of the four species of Bulinus found on Madagascar, three species: B. obtusispira, B. liratus and B. bavayi are endemic while the fourth, B. forskalii, is probably a recent introduction from the African mainland. The evolutionary relationships of these species with Bulinus species from Africa were studied by phylogenetic analysis of DNA sequence variation at two mitochondrial loci: cytochrome oxidase subunit I (COI) and large ribosomal subunit (LSU) or 16S. The observed levels of nucleotide divergence within Bulinus were substantial but may underestimate the true levels as there was evidence of 'saturation' of transitional substitutions at both loci. A putative secondary structure model for the sequenced segment of the 16S was developed. Subsequent phylogenetic analysis using transversional changes only for both loci, showed that there were contrasting levels of divergence within the four species groups. B. obtusispira was consistently placed within the B. africanus group, appearing ancestral to this group and was closest to the basal node within Bulinus. Together with B. bavayi, the two species appear to have been isolated on Madagascar for a long time, contrasting with both B. liratus and B. forskalii that appear more recent colonisers; however, estimate of exact times of divergence is problematic. A PCR-RFLP assay was developed to enable identification and discrimination of B. obtusispira and B. liratus using discriminatory variation within the COI. To enable population genetic analysis within B. obtusispira, microsatellite markers were developed using an enrichment method and 8 primer pairs are reported. Laboratory infection experiments using Madasgacan S. haematobium from the Mahabo area showed that certain populations of B. obtusispira, B. liratus and B. bavayi were compatible.

Conserved sequence patterns in the non-coding ribosomal ITS-1 of distantly related snail taxa

The ensuing contribution gives an insight into the evolution of non-coding ribosomal DNA of two distantly related groups of snails. The non-coding sequences of the ribosomal DNA comprise the First Internal Transcribed Spacer (ITS-1), the Second Internal Transcribed Spacer (ITS-2), and the NonTranscribed Spacer (NTS). These spacers are known to evolve faster than the coding 18S, 5.8S and 28S ribosomal DNA1,2,3. The fast evolution of the spacers can be used to investigate the genetic relationships of closely related genera, species and other lower taxonomic units with a divergence time of less than 50 million years3,4,5. The focus of our analysis is on the evolution of the ITS-1 of land snails (Stylommatophora) and of freshwater snails (Basommatophora). These two snail groups have their origin in the Mesozoic. Consequently, we expected their ITS-1 sequences to show strong differences. However, the ITS-1 of stylommatophoran and basommatophoran gastropods is consecutively divided into conserved and variable regions. The detection of conserved ITS-1 regions among distantly related animals gives further insight into the functional significance of non-coding ribosomal RNA. In the analysis, all published ITS-1 sequences of stylommatophoran and basommatophoran gastropods are taken into consideration. These include the sequences of two species of Albinaria, two species of Isabellaria (Stylommatophora; Clausiliidae)6, three species of Bulinus (Basommatophora; Planorbidae)7, and four species of Stagnicola (Basommatophora; Lymnaeidae)8. In addition, we sequenced the ITS-1 of the following five species (protocols are available on request): three species of Cochlicopa (Stylommatophora; Cochlicopidae), Azeca goodalli (Stylommatophora; Cochlicopidae), and two specimens of Arianta arbustorum (Stylommatophora; Helicidae) (accession numbers: Y16755–Y16765; AF124052–AF124053). The sequences were aligned with the program CLUSTAL W, version 1.5, in order to find homologous regions in all taxa see 9. The sequence alignment clearly shows that conserved sequence regions and variable regions occur inthe ITS-1 of stylommatophoran and basommatophoran gastropods. Only a few alignment positions had to be corrected manually. Six conserved blocks, I to VI, ranging in size from 15 to 28 nucleotides were found. Both the relative position (Figure 1) and the respective sequences are highly similar among the taxa (over 80 percent sequence similarity in pairwise RESEARCH NOTES

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.

Intraspecific diversity of Schistosoma haematobium in West Africa: chronobiology of cercarial emergence

Cercarial emergence patterns were used to analyse the intraspecific variability within and between nine populations of Schistosoma haematobium collected along a transect line from the North to the South of the Ivory Coast (Africa) and using Bulinus truncatus or Bulinus globosus as intermediate snail hosts. Statistical comparison demonstrated the existence of a chronobiological polymorphism and the existence of three homogenous groups of S. haematobium isolates with mean shedding times of the cercariae decreasing from the North to the South. The chronobiological variability observed was not correlated with the species of Bulinus ( B. truncatus vs. B. globosus) implicated in the parasite transmission but with the climatic and vegetal features of the transmission areas. S. haematobium from shaded sites of the forest zone (South) showed cercarial emergence patterns significantly earliest than that of S. haematobium from open sites of the savanna zone (North). Differences in sensitivity to light intensity could characterize the existence of eco-geographical races of S. haematobium one of the forest, the other from the savanna.

AN EVALUATION OF RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) FOR THE IDENTIFICATION AND PHYLOGENY OF FRESHWATER SNAILS OF THE GENUS BULINUS (GASTROPODA: PLANORBIDAE)

The Random Amplified Polymorphic DNA (RAPD) assay was used to study genetic variation within and between 9 species of the genus Bulinus and to determine whether RAPD profiles could be used as markers for identification purposes. RAPDs were generated with 8 primers of two different sizes (lOmers & 15mers) and were visualised using both polyacrylamide gel electrophoresis (PAGE) with silver staining and agarose gel electrophoresis with ethidium bromide staining. The species groups of Bulinus had few similarities in their RAPD profiles and there was interspecific variation within groups. Intrapopulation variation was observed, with all primers, for B globosus collected from a single site in Zimbabwe PAGE/silver staining methods visualised a greater number of RAPDs in comparison with agarose/ethidium bromide methods. Phenetic analysis indicated that distance estimates between taxa were sometimes non-additive and the phylogenetic analysis of such non-metnc data is discussed. The resultant phenograms, constructed using a least squares method, were constrained almost into a polytomy with topologies often differing between data sets. It was concluded that this phenomenon was most likely attributable to large nucleotide divergences between the species groups which go beyond the phylogenetic scope of RAPD analysis. RAPD profiles, when used in conjunction with other taxonomic methods, may contribute to the identification of species of Buhnus on a regional basis, but the observed variability in a natural population suggests that a diagnostic RAPD profile for each species throughout its geographic range is unlikely.

Schistosomiasis in the Republic of São Tomé and Principe: characterization of Schistosoma intercalatum

This paper reports the morphological and biochemical characterization of the species of Schistosoma infecting humans in the Republic of São Tomé and Principe. The eggs are typical in shape and size of S. intercalatum, measuring on average between 174·5 μm and 189·1 μm. The eggs are voided in the faeces and not the urine of infected people. The parasite experimentally develops in several different species of Bulinus belonging to the B. forskalii group, including B. forskalii, with a minimum prepatent period of 25 d, and also in snails of the B. reticulatus group ( B. wrighti); it is incompatible with snails of the B. africanus and B. truncatus/B. tropicus complex. A survey of 5 different habitats at intervals of 2 weeks over a period of one year showed that populations of B. forskalii increased during the dry period of June, July and August in 1988, and in 3 of the habitats snails were present throughout the year. Hence transmission may take place in these habitats throughout the year. Preliminary evidence suggests that water velocity is a limiting factor confining Bulinus to the north-east of the island where the terrain is less mountainous. Development of schistosomes from São Tomé was followed in experimentally infected hamsters. The cross-over point (the point at which the paired male and female worms are of the same average length) occurred at about 49 d after infection: eggs were first seen in the uteri of the female worms 48 d after infection. The parasite from São Tomé developed in sheep and produced viable eggs. Analysis of restriction fragments of the rRNA gene clearly differentiated the São Tomé parasite from S. haematobium. Comparative scanning electron microscopy studies of the surface of the male worms of isolates from São Tomé revealed tubercles with spines, but with some variation in the degree of spination. A study of 9 different enzymes using isoelectric focusing indicated that hexokinase, acid phosphatase, and glucose-6-phosphate dehydrogenase were monomorphic in the São Tomé schistosome. Intra-specific variation was noted for phosphoglucomutase, glucose phosphate isomerase, α-glycerophosphate dehydrogenase, adenylate kinase, lactate dehydrogenase, and malate dehydrogenase. These observations confirm the identity of the human schistosome in São Tomé as S. intercalatum.

The sugar chemoreception niches of Bulinus (physopsis) globosus (morelet) and Bulinus rohlfsi (clessin), the two most important snail hosts of Schistosoma haematobium (Bilharz) in West Africa

1. 1.The behavioural responses of two species of freshwater pulmonate snails Bulinus (P.) globosus and Bulinus rohlfsi] to sugar gradients were investigated by means of diffusion olfactometers. 2. 2.Both snail species proved to be very discriminating in their responses. Of the 17 sugars tested, 35.3%, namely d(−)glucuronic, maltotriose, maltose, cellobiose, d(−)arabinose, d(+)mannose proved to be statistically significant attractants or arrestants to B. rohlfsi. Only 23.5% of these sugars (maltotriose, maltose), d(+) mannose and d(+) xylose were significant attraetants or arrestants to B. (P.) globosus. 3. 3.Glucuronic acid was a significant repellent to B. rohlfsi but none of the sugars was a repellent to B. (P.) globosus. 4. 4.The results are compared with those obtained for other snail species and their relevance to the ecology and control of the snails are discussed.

Cytogenetics and Biology of the Intermediate Host of Human Bilharziasis, Bulinus truncatus Common in Upper Egypt.

Species of the qenus Bulinus occur as a polyploid series which is of interest because of the rarity of polyploidy in the animal kingdom and because it appears that there is some kind of relationship between polyploidy and the ability of this genus to transmit schistosomiasis, a parasitic disease of a major public health importance in most developing coutries. Chromosome analyses were performed in preparations of gonads, gills and embryos, from a hunded specimens of Bulinus truncatus which were collected from different localities around Qena City. The diploid chromosome number was determined to be seventy two (2n=72). The karyotype was made up of seventeen metacentric, thirteen submetacentric, three subtelocentric and three telocentric chromosome pairs. Considering previously reported cytogenetic data in the genus Bulinus, the present specimene appear to represent a tetraploid form and this is the first report in which detailed karyotype for Bulinus truncatus is presented. Habitat, morphological characters and shell measurements for this species are also described in detail in this paper.

FRESHWATER SNAILS OF THE BULINUS TRUNCATUS/TROPICUS COMPLEX (BASOMMATOPHORA: PLANORBIDAE) IN KENYA: DIPLOID POPULATIONS

Freshwater snails of the Bulinustruncatus/tropicus complex occur in Kenya as diploid and tetraploid forms which may not noticeably differ in the shell. This account provides data for diploid snails, on geographical distribution, inter-population variation, taxonomy and identification. Observations were made for 65 populations (40 newly reported) on egg proteins, body surface mucus, enzymes (5 systems), shell (10 variables), male genital system (normal or aphallic) and radula (1st lateral tooth; size and meso-cone shape). Two snail populations sampled were known to carry the trematode parasites Schistosoma bovis and Calicophoron microbothrium. All the diploid populations sampled appeared con-specific from their overall continuity in morphological variation and its lack of geographical pattern, and the observation of interbreeding between snails of contrasting morphology. On the other hand, there were considerable interpopulation differences in shell form, mesocone shape and enzymes. A distinct shell form (corresponding to Physa rumrutiensis Preston) is associated with seasonal rainpools. Some Kenyan populations have the mesocone commonly angular in shape, in this respect resembling B. natalensis. The entire range of forms is here classified as B. tropicus, but future subdividing of this taxon is not unlikely. Reasons are advanced for regarding as diploid, taxa of Bulinus named by Dautzenberg (alluaudi) and by Preston either validly (exserta, laikipiaensis, rumrutiensis, syngenes) or in manuscript(baringoensis, congener). The status of the taxa B. natalensis and B. zanzebaricus is discussed. Morphometry did not reveal any clear difference by which all forms of B. tropicus could be separated from both the tetraploid species B. truncatus and B. permembranaceus. Each species does have characteristic enzyme types (AcP, HBDH, MDH and GPI). B. tropicus is widely distributed in Kenya and is common in some areas where other species of Bulinus are rare or absent, but it is surprisingly not found in the coastal region.

The potential role of various species of intermediate hosts of Schistosoma haematobium in Saudi Arabia

The potential role of 3 species of Bulinus in the transmission of Schistosoma haematobium in Saudi Arabia was assessed on the basis of their susceptibility to experimental infection, their geographical distribution and numbers, and die type of habitats in which they were found. B. truncatus, distributed mainly in the mid- and south-western regions, showed extremely low susceptibility to strains of S. haematobium from Yemen, Egypt and Sudan. The same species from one area in the north-west was refractory to a strain of die parasite from Yemen. In contrast, B. wrighti was very susceptible to infection but is found only in a few habitats far from human settlements, thus probably playing little part in the transmission of die disease. As B. beccarii is highly susceptible to the infection and is distributed widely, this snail is probably the main intermediate host of schistosomiasis in Saudi Arabia.

Schistosoma bovis: Variability of cercarial production as related to the snail hosts: Bulinus truncatus, B. wrighti and Planorbarius metidjensis

Development of Schistosoma bovis from Spain in different species or genus of intermediate hosts ( Bulinus truncatus, B. wrighti and Planorbarius metidjensis) modifies cercarial productivity and its dynamics. From B. truncatus to B. wrighti and to P. metidjensis, cercarial productivity decreases while the length of the production period is increased. Variations in the dynamics are less obvious between the two species of Bulinus than between Bulinus spp. and P. metidjensis. In the latter the emission pattern is characterized by a 45–48-day production rhythm. These differences are explained in terms of larval demographic strategies and biotic capacities of the hosts. The validity of employing cercarial production as an indicator of host-parasite compatibility is discussed.

Experimental taxonomy of Bulinus (Gastropoda: Planorbidae): the West and North African species reconsidered, based upon an electrophoretic study of several enzymes per individual

Horizontal starch gel electrophoresis was used to score mobilities of seven different enzymes in species of Bulinus from North and West Africa. An account of the intra- and inter-population variation observed was given. Based on the data obtained it was suggested that enzymic data should be used as taxonomic characters in parallel with morphological and anatomical characters. It is suggested that enzymic characters could be used to place taxa into synonymy if the data are collected in such a way that one can write up an enzyme profile for the single individual. The nine taxa of Bulinus known to occur in North and West Africa were revised, the taxon B. jousseaumei was synonymized with B. globosus, and the two taxa B. guernei and B. rohlfsi were synonymized with B. truncatus. As a result of the revision only six species could be recognized as valid from the area, these being B. forskalii, B. globosus, B. senegalensis, B. truncatus, B. ugandae and B. umbilicatus. Finally, some enzymic characters are suggested that may be used for a reliable identification of these morphologically very difficult taxa.