Phylogeny of seven Bulinus species originating from endemic areas in three African countries, in relation to the human blood fluke Schistosoma haematobium.

BACKGROUND: Snails species belonging to the genus Bulinus (Planorbidae) serve as intermediate host for flukes belonging to the genus Schistosoma (Digenea, Platyhelminthes). Despite its importance in the transmission of these parasites, the evolutionary history of this genus is still obscure. In the present study, we used the partial mitochondrial cytochrome oxidase subunit I (cox1) gene, and the nuclear ribosomal ITS, 18S and 28S genes to investigate the haplotype diversity and phylogeny of seven Bulinus species originating from three endemic countries in Africa (Cameroon, Senegal and Egypt). RESULTS: The cox1 region showed much more variation than the ribosomal markers within Bulinus sequences. High levels of genetic diversity were detected at all loci in the seven studied species, with clear segregation between individuals and appearance of different haplotypes, even within same species from the same locality. Sequences clustered into two lineages; (A) groups Bulinus truncatus, B. tropicus, B. globosus and B. umbilicatus; while (B) groups B. forskalii, B. senegalensis and B. camerunensis. Interesting patterns emerge regarding schistosome susceptibility: Bulinus species with lower genetic diversity are predicted to have higher infection prevalence than those with greater diversity in host susceptibility. CONCLUSION: The results reported in this study are very important since a detailed understanding of the population genetic structure of Bulinus is essential to understand the epidemiology of many schistosome parasites.

Molecular approaches to the identification of Bulinus species in south-west Nigeria and observations on natural snail infections with schistosomes.

The current study considers the distribution of a small sample of 138 Bulinus snails, across 28 localities within eight Nigerian states. Snails were identified using a combination of molecular methods involving both DNA sequencing of a partial cytochrome oxidase subunit 1 (cox1) fragment and restriction profiles obtained from ribosomal internal transcribed spacer (its) amplicons. The results showed that the majority of Bulinus samples tested belonged to the species Bulinus truncatus while only two were Bulinus globosus. The use of RsaI restriction endonuclease to cleave the ribosomal its of Bulinus, as a method of species identification, was adopted for the majority of samples, this being a quicker and cheaper method better suited to small laboratory environments. Polymerase chain reaction (PCR) amplification of the schistosome Dra1 repeat within each of the collected Bulinus samples was employed to determine the extent and distribution of infected snails within the sample areas. Successful amplification of the Dra1 repeat demonstrated that 29.7% of snails were infected with schistosomes. Sequencing of the partial schistosome its from a small subset of snail samples suggested that some snails were either penetrated by both Schistosoma haematobium and Schistosoma bovis miracidia or hybrid miracidia formed from the two species.

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.

Assessing the diversity and distribution of potential intermediate hosts snails for urogenital schistosomiasis: Bulinus spp. (Gastropoda: Planorbidae) of Lake Victoria.

BACKGROUND: The Lake Victoria basin is one of the most persistent hotspots of schistosomiasis in Africa, the intestinal form of the disease being studied more often than the urogenital form. Most schistosomiasis studies have been directed to Schistosoma mansoni and their corresponding intermediate snail hosts of the genus Biomphalaria, while neglecting S. haematobium and their intermediate snail hosts of the genus Bulinus. In the present study, we used DNA sequences from part of the cytochrome c oxidase subunit 1 (cox1) gene and the internal transcribed spacer 2 (ITS2) region to investigate Bulinus populations obtained from a longitudinal survey in Lake Victoria and neighbouring systems during 2010-2019. METHODS: Sequences were obtained to (i) determine specimen identities, diversity and phylogenetic positions, (ii) reconstruct phylogeographical affinities, and (iii) determine the population structure to discuss the results and their implications for the transmission and epidemiology of urogenital schistosomiasis in Lake Victoria. RESULTS: Phylogenies, species delimitation methods (SDMs) and statistical parsimony networks revealed the presence of two main groups of Bulinus species occurring in Lake Victoria; B. truncatus/B. tropicus complex with three species (B. truncatus, B. tropicus and Bulinus sp. 1), dominating the lake proper, and a B. africanus group, prevalent in banks and marshes. Although a total of 47 cox1 haplotypes, were detected within and outside Lake Victoria, there was limited haplotype sharing (only Haplotype 6 was shared between populations from Lake Victoria open waters and neighbouring aquatic systems) - an indication that haplotypes are specific to habitats. CONCLUSIONS: The Bulinus fauna of Lake Victoria consists of at least B. truncatus, B. tropicus, Bulinus sp. 1 (B. trigonus?) and B. ugandae. The occurrence and wide distribution of Bulinus species in Lake Victoria potentially implies the occurrence of urogenital schistosomiasis in communities living along the shores and on islands of the lake who depend solely on the lake for their livelihood. More in-depth studies are needed to obtain a better picture of the extent of the disease in the Lake Victoria basin.

Molecular identification of Bulinus spp. intermediate host snails of Schistosoma spp. in crater lakes of western Uganda with implications for the transmission of the Schistosoma haematobium group parasites.

BACKGROUND: Human schistosomiasis is the second most important tropical disease and occurs in two forms in Africa (intestinal and urogenital) caused by the digenetic trematodes Schistosoma mansoni and Schistosoma haematobium, respectively. A proposed recent shift of schistosomiasis above a previously established altitudinal threshold of 1400 m above sea level in western Ugandan crater lakes has triggered more research interest there. METHODS: Based on extensive field sampling in western Uganda and beyond and employing an approach using sequences of the mitochondrial barcoding gene cytochrome c oxidase subunit 1 (cox1) this study aims were: (i) identification and establishment of the phylogenetic affinities of Bulinus species as potential hosts for Schistosoma spp.; (ii) determining diversity, frequency and distribution patterns of Bulinus spp.; and (iii) establishing genetic variability and phylogeographical patterns using Bayesian inference and parsimony network analyses. RESULTS: Out of the 58 crater lakes surveyed, three species of Bulinus snails were found in 34 crater lakes. Bulinus tropicus was dominating, Bulinus forskalii was found in two lakes and Bulinus truncatus in one. The latter two species are unconfirmed potential hosts for S. haematobium in this region. However, Bulinus tropicus is an important species for schistosomiasis transmission in ruminants. Bulinus tropicus comprised 31 haplotypes while both B. forskalii and B. truncatus exhibited only a single haplotype in the crater lakes. All species clustered with most of the haplotypes from surrounding lake systems forming source regions for the colonization of the crater lakes. CONCLUSIONS: This first detailed malacological study of the crater lakes systems in western Uganda revealed presence of Bulinus species that are either not known or not regionally known to be hosts for S. haematobium, the causing agent of human urogenital schistosomiasis. Though this disease risk is almost negligible, the observed dominance of B. tropicus in the crater lakes shows that there is a likelihood of a high risk of infections with Schistosoma bovis. Thus, extra attention should be accorded to safeguard wild and domestic ruminants in this region as the population benefits from these animals.

Molecular phylogeny of diploid Bulinus sp. (Gastropoda: Planorbidae) populations in Cameroon crater lakes.

Bulinus sp. (2n=36) is a diploid freshwater snail found in Cameroon crater lakes; it belongs to a group of medically important freshwater snails. Some members (Bulinus truncatus, Bulinus tropicus) of this group had been reported to be involved in the transmission of parasites (Schistosoma sp. and Calicophoron microbothrium) to human and livestock in tropical Africa. Yet, understanding of the evolutionary identity of the diploid snail such as its phylogenetic position and the genetic divergence among populations, remains limited. In this study, we constructed the molecular phylogeny of Bulinus sp. using sequences of mitochondrial cytochrome oxydase subunit 1 (CO-1, 365 nucleotides). Partial sequences of CO-1 were obtained and genetic divergences between populations estimated after the alignment of 365 nucleotides from each studied population. The lack of deep molecular divergences between populations of Bulinus sp. from western Cameroon crater lakes may indicate that they belong to the same lineage; therefore, it implies that diploid B. truncatus/tropicus complex snail-like in Cameroon share a common ancestor. The CO-1 of the three studied populations of Bulinus sp., clustered together with other diploid pan-African representatives of the B. truncatus/tropicus complex, showed little evidence of genetic similarities.

Mapping freshwater snails in north-western Angola: distribution, identity and molecular diversity of medically important taxa.

BACKGROUND: This study was designed to determine the distribution and identity of potential intermediate snail hosts of Schistosoma spp. in Bengo, Luanda, Kwanza Norte and Malanje Provinces in north-western Angola. This is an area where infection with Schistosoma haematobium, causing urogenital schistosomiasis, is common but little is yet known about transmission of the disease. Angola has had a varied past with regard to disease control and is revitalising efforts to combat neglected tropical diseases. METHODS: Snails were sampled from 60 water-contact points. Specimens of the genera Bulinus, Biomphalaria or Lymnaea were screened for trematode infections by inducing cercarial shedding. Snails were initially identified using shell morphology; subsequently a cytochrome c oxidase subunit 1 (cox1) gene fragment was amplified from a subset of snails from each site, for molecular identification. Cercariae were captured onto FTA cards for molecular analysis. Specimens of Bulinus angolensis collected from the original locality of the type specimen have been characterised and comparisons made with snails collected in 1957 held at the Natural History Museum, London, UK. RESULTS: In total snails of nine genera were identified using morphological characteristics: Biomphalaria, Bulinus, Gyraulus, Lanistes, Lentorbis, Lymnaea, Melanoides, Physa and Succinea. Significant for schistosomiasis transmission, was the discovery of Bulinus globosus, B. canescens, B. angolensis, B. crystallinus and Biomphalaria salinarum in their type-localities and elsewhere. Bulinus globosus and B. angolensis occurred in two distinct geographical areas. The cox1 sequence for B. globosus differed markedly from those from specimens of this species collected from other countries. Bulinus angolensis is more closely related to B. globosus than originally documented and should be included in the B. africanus group. Schistosoma haematobium cercariae were recovered from B. globosus from two locations: Cabungo, Bengo (20 snails) and Calandula, Malanje (5 snails). Schistosoma haematobium cercariae were identified as group 1 cox1 corresponding to the type common throughout the African mainland. CONCLUSIONS: Various freshwater bodies in north-western Angola harbour potential intermediate snail hosts for urogenital schistosomiasis, highlighting the need to map the rest of the country to identify areas where transmission can occur and where control efforts should be targeted. The molecular phylogeny generated from the samples confirmed that considerable variation exists in B. globosus, which is the primary snail host for S. haematobium in many regions of Africa.

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.

Population genetic structure of the freshwater snail, Bulinus globosus, (Gastropoda: Planorbidae) from selected habitats of KwaZulu-Natal, South Africa.

The freshwater snail Bulinus globosus is an important intermediate host of Schistosoma haematobium, the causative agent of urinary schistosomiasis. This disease is of major health concern, especially in Africa where the majority of cases have been reported. In this study the inter- and intra-genetic diversity and population genetic structure of B. globosus from nine locations in the KwaZulu-Natal province of South Africa was studied using four polymorphic microsatellite loci (BgZ1-BgZ4). Moderate genetic diversity was detected within populations with a mean diversity (HE) of 0.49±0.09. The majority of populations significantly deviated from Hardy-Weinberg equilibrium (p<0.05), due to a deficit of heterozygotes. Such deviations may be due to founder events that were caused by bottlenecks that occurred as a result of frequent droughts and flooding that these snails' habitats are exposed to. Overall, the populations studied seem to be partially inbreeders/selfers with mean estimates of 0.24/0.38. A discernable genetic structure was elucidated among populations as evident by the mean pairwise FST of 0.58±0.13. There was no significant association between genetic and geographical distance among populations, an indication of limited gene flow. This increases the chances of populations losing alleles due to genetic drift. Populations in close proximity demonstrated high genetic differentiation (58.77% total variation) due to allelic differences between them. The sample populations fell into 12 clusters, however, the populations from uMkhanyakude and uThungulu exhibited no discernable genetic structure. Genetically, the Bhobhoyi site found within the uGu district was equidistant to the two main sampling regions.

Enzyme analyses of Bulinus africanus group snails (Mollusca: Planorbidae) from Tanzania.

38 population samples of snails of the Bulinus africanus group, collected from three separate areas of Tanzania, have been examined. Enzymes in crude digestive gland extracts of individual snails have been analysed by isoelectric focusing in polyacrylamide gels. The enzymes studied were: malate dehydrogenase (MDH); phosphoglucomutase (PGM); glucosephosphate isomerase (GPI); acid phosphatase (AcP) and hydroxybutyrate dehydrogenase (HBDH). Samples of B. nasutus were clearly differentiated from other species and enzyme differences were apparent between samples from the lake and coastal areas. Similarly, although clear distinctions could not always be made, samples of B. africanus, B. globosus and B. ugandae were characterized by their enzyme types. Individual variation was detected within populations and the significance of enzyme polymorphisms in relation to identification has been considered. No correlation was found between snail enzyme type and susceptibility to Schistosoma haematobium or S. bovis.

A comparison of Bulinus africanus group species (Planorbidae; Gastropoda) by use of the internal transcribed spacer 1 region combined by morphological and anatomical characters.

The morphological and anatomical characters applied to determine species identity in the Bulinus africanus group species are insufficient to unambiguously discriminate between arbitrary species of given populations. In order to solve this problem, four snail populations from Kenya have been investigated morphologically and anatomically, and the species status compared with the result of molecular methods. We have amplified the entire ITS region and found that the investigated populations showed intra-specific genetic polymorphism, thereby giving the taxa an identity which were indistinct when the region was cut with restriction enzymes. Instead, an amplification of the sub-region ITS 1 revealed an unambiguous identification. because the amplification revealed only one single fragment. We also found that the observed heterogeneity of the entire ITS region could be confined to the sub-region ITS 2. Furthermore, the micro-sculpture of the shell and penis to preputium proportion, which are normally applied as morphological characters, might be considered as inadequate, because of the lack of a significant difference in those characters between the two well established species, namely B. africanus and B. nasutus in the Kisumu area. Instead, these two taxa were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to be one single species with a highly variable morphology. This result was further confirmed by random amplified polymorphic DNA (RAPD) data and the mitochondrial cytochome oxidase subunit I (COI).

Miracidia of an Egyptian strain of Schistosoma mansoni differentiate between sympatric snail species.

The host-finding behavior of miracidia of 2 strains of Schistosoma mansoni from Egypt and Brazil was studied by recording their responses to snail-conditioned water (SCW) from the Egyptian sympatric snails, Biomphalaria alexandrina, Physa acuta, Lymnaea cailliudi, and Balinus truncatus, as well as from Biomphalaria arabica and Biomphalaria glabrata. Miracidia of the Egyptian strain significantly preferred SCW from their compatible hosts B. alexandrina and B. arabica and showed no or a weak response to SCW from the other sympatric species, whereas miracidia of the Brazilian strain did not differentiate between SCW from different snail species.

[Mollusc vectors of schistosomiasis in Sardinia and in the Mediterranean area: taxonomy and epidemiology]. / Ricerche sui molluschi vettori di schistosomiasi in Sardegna e nell'area Mediterranea: problemi tassonomici ed epidemiologici.

The present classification of molluscs, intermediate hosts of Schistosoma in the Mediterranean area (subfamily Bulininae), based on morphological characters of shell, radula teeth and soft anatomy is unsatisfactory. The electrophoretical study of gene-enzyme systems of many strains of different species of genus Bulinus has enabled us in 1979 to split this genus in three well differentiated genera: Bulinus, Physopsis and Isidora (syn. Mandahlbarthia). All the populations of I. truncata at our disposal (from Sardinia, Egypt, Lybia Morocco, etc.) have been genetically studied comparing gene-enzyme systems of each one of them with those of an egyptian reference strain, collected in Giza near Cairo (Egypt). The presence of many genetically well differentiated biotypes has been observed, confirming that Isidora truncata must be regarded as a complex; only in Sardinia have been found 6 genetically differentiated biotypes. The names of the subspecies of Isidora truncata (for instance Isidora truncata, rivularis, etc) have, in our opinion, no taxonomical significance, because it is not possible to identify them morphologically, biologically, serologically, etc. To the contrary the locality of origin of every population of I. truncata complex, followed by the discriminating gene-enzyme systems gives a genetical identification of obvious epidemiological interest.

[Morphological, biological and biochemical study of a new species of Bulinus (Gastropoda: Planorbidae)]. / Studi morfologici, biologici e biochimici su una nuova specie di Bulinus (Gastropoda: Planorbidae).

A description is given of Bulinus yemenensis, a new species from Yemen belonging to the truncatus group. B. yemenensis is morphologically and biologically differenciated from B. truncatus truncatus, from which it is also electrophoretically distinguishable on the basis of the following enzyme loci: Est-2, Est-3, Pgm-2 and 6-Pgdh among the 26 analysed.

[Schistosoma species in Senegal with special reference to the biology, epidemiology and pathology of Schistosoma curassoni Brumpt, 1931]. / De Schistosoma-soorten in Senegal met een speciale verwijzing naar de biologie, epidemiologie en pathologie van Schistosoma curassoni Brumpt, 1931.

By combining field and experimental investigations, we were able to study several new aspects of fundamental problems concerning human and animal schistosomiasis in Senegal. Because of the controversy about the identity of Schistosoma curassoni and the possibly connected zoonosis, this parasite has been described once more. A great variety of experimental techniques were used. The eggs of S. curassoni are significantly smaller than those of the two other African species of Schistosoma we know of in ruminants (S. bovis and S. mattheei). But eggs of S. curassoni cannot be distinguished from those of the human, pathogenic S. haematobium. The study of the tegument of adult male worms shows a clear difference between S. bovis on one hand, and S. curassoni and S. haematobium on the other hand. S. bovis' tubercles are well formed, but have no stings at all. The tubercles of S. haematobium and of S. curassoni definitely possess stings. S. curassoni, S. haematobium and S. bovis are also clearly different as to their development in hamsters (Mesocricetus auratus). S. curassoni develops more rapidly and gets bigger than S. bovis and S. haematobium. Finally, different enzymatic systems allow us to distinguish S. curassoni from other schistosoma's of the haematobium group. S. curassoni has a typical pattern for phosphoglucomutase and hexokinase, differing from S. haematobium's patterns. In S. bovis, it differs by the patterns of phosphoglucomutase, glucosephosphate-isomerase, hexokinase and acid phosphatase. Epidemiological studies proved that, in Senegal, Bulinus guernei is the main vector of S. bovis, Bulinus senegalensis of S. haematobium (Northern Senegal) and Bulinus umbilicatus of S. curassoni and S. haematobium (Southern Senegal). There is no indication to consider S. curassoni as a zoonosis. When ruminants are infested by S. curassoni, the symptoms are light and the most important lesions can be found in the liver, the intestines and, in a lesser degree, in the bladder. S. curassoni develops easily in laboratory animals, giving severe lesions in liver and bowels. That makes it an interesting new model for studying the pathogenesis of schistosomes of the haematobium group and the action of new anthelmintics to be used against them.

Susceptibility of Ethiopian bulinid snails to Schistosoma haematobium from Somalia.

Susceptibility of four Ethiopian bulinid snails to a Somalian strain of S. haematobium was tested. Bulinus abyssinicus was highly susceptible and lowland B. africanus was partially susceptible while B. truncatus and B. forskalii were refractory to the parasite. It is suggested that Ethiopian refugees returning from Somalia and/or Somalian refugees entering Ethiopia should be screened and treated for S. haematobium before they are allowed to work/resettle in development areas where B. abyssinicus and B. africanus are known or ecologically suspected to occur.

[Experimental study of the compatibility between Schistosoma haematobium and two species of Bulinus in Cameroon]. / Etude expérimentale de la compatibilité entre Schistosoma haematobium et deux espèces de bulins au Cameroun.

A study on the compatibility between Schistosoma haematobium from three remote localities (Mourtourwa, Gounougou and Kékem) and four populations of Bulinus truncatus (Gounougou, Ngaoundéré, Bertoua and Kékem) and four populations of B. globosus (Mourtourwa, Ouroudoukoudje, Bafia and Yaoundé) was undertaken in order to estimate the risk of extension of urinary schistosomiasis in Cameroon. First generation of offspring from wild Bulinus was exposed to miracidia liberated by schistosome eggs extracted from patient urine. Between the 25th and the 60th day post-infestation the number of snails still alive, the number emitting cercariae and the prepatent period duration were noted. Results showed that all B. truncatus samples were susceptible to the three strains of parasite whereas only B. globosus of Mourtourwa and Ouroudoukoudje were susceptible to S. haematobium from Mourtourwa. The schistosome infection rate was then significantly higher in B. truncatus and the prepatent period significantly lower than in B. globosus. The compatibility characterised by a high infection rate and a low prepatent period was significantly better in homopatric couples than in allopatric combinations. The results suggested that B. truncatus might be potentially more implicated than B. globosus to the extension of the urinary bilharziasis in Cameroon.

[The distribution of freshwater molluscs the intermediate hosts of human schistosomas in Katan, south-Kivu]. / Distribution des mollusques dulcicoles hotes intermédiairies des schistosomes humains à Katana, sud-Kivu.

In eastern Democratic Republic of Congo, the prevalence of bilharziasis due to Schistosoma mansoni is high along the Kivu lake shoreline where Biomphalaria pfeifferi, i.e. the intermediate host of Schistosoma mansoni, is the only snail that has been described until now. Although their occurrence has not been reported in the area, other schistosomas remain possible since their intermediate hosts are present. This study was carried out in 1992 to determine the distribution of intermediate host snails in freshwater systems in the region. Samples were collected according to the standardized harvest time unit method. Five species of intermediate host snails for human schistosomiasis were identified. By far the most prevalent species was Biomphalaria pfeifferi which was found in 75% of the freshwater systems studied. Given the presence of Schistosoma mansoni in the region, spread of this type of schistosome is likely. Ferrissia burnipi, the recognized intermediate host of Schistosoma haematobium, was observed in association with Biomphalaria pfeifferi. Snails of the Bulinus genus were confined to special environments. Factors preventing infestation by Schistosoma haematobium and Schistosoma intercalatum remain unclear. Control measures against snails and their larvae in fresh water systems in the region are needed to stop the spread of Schistosoma mansoni and prevent the appearance of Schistosoma haematobium and Schistosoma intercalutum.

Significant population genetic structure of the Cameroonian fresh water snail, Bulinus globosus, (Gastropoda: Planorbidae) revealed by nuclear microsatellite loci analysis.

In order to characterize the demographic traits and spatial structure of Cameroonians Bulinus globosus, intermediate host of Schistosoma haematobium, genetic structure of seven different populations, collected from the tropical zone, was studied using six polymorphic microsatellites. Intrapopulation genetic diversity ranged from 0.37 to 0.55. Interpopulation genetic diversity variation clearly illustrated their significant isolation due to distance with gene flow substantially limited to neighbouring populations. The effective population sizes (Ne) were relatively low (from 3.0 to 18.6), which supposes a high rate from which populations would lose their genetic diversity by drift. Analysis of genetic temporal variability indicated fluctuations of allelic frequencies (35 of 42 locus-population combinations, P<0.05) characteristic of stochastic demography, and this is reinforced by events of bottlenecks detected in all populations. These findings demonstrated that Cameroonian B. globosus were mixed-maters with some populations showing clear preference for outcrossing. These data also suggest that genetic drift and gene flow are the main factors shaping the genetic structure of studied populations.

Bulinus globosus (Planorbidae; Gastropoda) populations in the Lake Victoria basin and coastal Kenya show extreme nuclear genetic differentiation.

Bulinus globosus, a key intermediate host for Schistosoma haematobium that causes urinary schistosomiasis, is a hermaphroditic freshwater Planorbid snail species that inhabits patchy and transient water bodies prone to large seasonal variations in water availability. Although capable of self-fertilizing, this species has been reported to be preferentially out crossing. In this study, we characterized the population genetic structure of 19 B. globosus populations sampled across the Lake Victoria basin and coastal Kenya using four polymorphic microsatellite loci. Population genetic structure was characterized and quantified using FST statistics and Bayesian clustering algorithms. The four loci used in this study contained sufficient statistical power to detect low levels of population genetic differentiation and were highly polymorphic with the number of alleles per locus across populations ranging from 16 to 22. Average observed and expected heterozygosities across loci in each population ranged from 0.13 to 0.69 and from 0.39 to 0.79, respectively. Twenty-five of the seventy-six possible population-locus comparisons significantly deviated from Hardy-Weinberg equilibrium proportions after Bonferroni corrections, mostly due to the deficiency of heterozygotes. Significant genetic differentiation was observed between populations and Bayesian inferences identified 15 genetic clusters. The excess homozygosity, significant inbreeding and population genetic differentiation observed in B. globosus populations are likely to be due to the habitat patchiness, mating system and the proneness to cyclic extinction and recolonization in transient habitats.