Genus Bulinus Research Articles

Exploring the genome-wide transcriptomic responses of Bulinus truncatus to Schistosoma haematobium infection: An important host-parasite system involved in the transmission of human urogenital schistosomiasis

Freshwater snails of the genus Bulinus are critical hosts for Schistosoma haematobium, the causative agent of urogenital schistosomiasis. Among the 37 recognized Bulinus species, B. truncatus is a key vector. Using RNA sequencing (RNAseq), we investigated the genome-wide transcriptional responses of B. truncatus to S. haematobium infection. Our findings suggest that snails employ a complex defense strategy against the parasites by up-regulating genes involved in immune response, stress reaction, structural integrity, metabolism, and detoxification. In response, schistosome parasites appear to manipulate the snail’s defense system, as evidenced by the suppression of immune-related genes such as ficolin, peptidoglycan recognition protein, and C-type lectin domain-containing protein genes. The down-regulation of biomphalysin 9, compared to its function in Biomphalaria glabrata, indicates divergent immune strategies among snail hosts. Additionally, we compared transcriptome profiles between embryos and juveniles, providing insights into developmental processes. This study offers valuable genomic data for Bulinus snails, illuminating the molecular interactions between bulinids and schistosomes, and advancing our understanding of their developmental biology.

Differentiation between Bulinus truncatus and Bulinus hexaploidus by morphological characters, chromosomal study and compatibility with Schistosoma haematobium.

Schistosomiasis is a snail-born, neglected tropical disease (NTD) caused by blood flukes (trematode worms) of the genusSchistosoma. It is the second most socioeconomically devastating parasitic disease after malaria. Urogenital schistosomiasis is caused by Schistosoma haematobium which is transmitted by snail intermediate host of the genus Bulinus. This genus is a model system for the study of polyploidy in animals. This study aims to investigate ploidy levels existing among the Bulinus species and their compatibility with S. haematobium. The specimens were collected from two governorates in Egypt. Chromosomal preparation was made from gonad tissue (ovotestis). This study found two ploidy levels (tetraploid, n=36 and hexaploid, n=54) of B. truncatus/tropicus complex in Egypt. Tetraploid B. truncatus was found in El-Beheira governorate while-unexpectedly and for the first time in Egypt, the hexaploid population was found in Giza governorate. This identification focused on shell morphology, chromosomal count, and spermatozoa of each species. Afterward, all species were exposed to S. haematobium miracidia where B. hexaploidus snails were the only refractory species. The histopathological study showed early destruction and abnormal development of S. haematobium in B. hexaploidus tissues. In addition, the hematological investigation showed increasing in the total hemocyte count, the formation of vacuoles, several pseudopodia, and more dense granules in the hemocytes of infected B. hexaploidus snails. In conclusion, there were two types of snails one was refractory and the other was susceptible.

Bulinus snails in the Lake Victoria Basin in Kenya: Systematics and their role as hosts for schistosomes.

The planorbid gastropod genus Bulinus consists of 38 species that vary in their ability to vector Schistosoma haematobium (the causative agent of human urogenital schistosomiasis), other Schistosoma species, and non-schistosome trematodes. Relying on sequence-based identifications of bulinids (partial cox1 and 16S) and Schistosoma (cox1 and ITS), we examined Bulinus species in the Lake Victoria Basin in Kenya for naturally acquired infections with Schistosoma species. We collected 6,133 bulinids from 11 sites between 2014-2021, 226 (3.7%) of which harbored Schistosoma infections. We found 4 Bulinus taxa from Lake Victoria (B. truncatus, B. tropicus, B. ugandae, and B. cf. transversalis), and an additional 4 from other habitats (B. globosus, B. productus, B. forskalii, and B. scalaris). S. haematobium infections were found in B. globosus and B. productus (with infections in the former predominating) whereas S. bovis infections were identified in B. globosus, B. productus, B. forskalii, and B. ugandae. No nuclear/mitochondrial discordance potentially indicative of S. haematobium/S. bovis hybridization was detected. We highlight the presence of Bulinus ugandae as a distinct lake-dwelling taxon closely related to B. globosus yet, unlike all other members of the B. africanus species group, is likely not a vector for S. haematobium, though it does exhibit susceptibility to S. bovis. Other lake-dwelling bulinids also lacked S. haematobium infections, supporting the possibility that they all lack compatibility with local S. haematobium, thereby preventing widespread transmission of urogenital schistosomiasis in the lake's waters. We support B. productus as a distinct species from B. nasutus, B. scalaris as distinct from B. forskalii, and add further evidence for a B. globosus species complex with three lineages represented in Kenya alone. This study serves as an essential prelude for investigating why these patterns in compatibility exist and whether the underlying biological mechanisms may be exploited for the purpose of limiting schistosome transmission.

First Molecular Identification of Bulinus africanus in Lake Malawi Implicated in Transmitting Schistosoma Parasites.

The freshwater snail genus Bulinus plays a vital role in transmitting parasites of the Schistosoma haematobium group. A hybrid schistosome between S. haematobium and S. mattheei has been recently detected using DNA-based identification methods in school children along the Lake Malawi shoreline in Mangochi District. This finding raised the need for contemporary revaluation of local interactions between schistosomes and snails, with a particular focus on snail species within the Bulinus africanus group. In 2017 and 2018, malacological surveys sampled several freshwater sites in Mangochi District. Collected snails (n = 250) were characterised using cytochrome oxidase subunit 1 gene (cox1), with DNA barcoding of the ‘Folmer’ region and a rapid PCR-RFLP typing assay with double digestion with HaeIII and SacI restriction enzymes. DNA cox1 sequence analysis, with phylogenetic tree construction, suggested the presence of at least three B. africanus group taxa in Lake Malawi, B. globosus, alongside first reports of B. africanus and B. angolensis, which can be differentiated by PCR-RFLP methods. In addition, a total of 30 of the 106 B. africanus group snails (28.30%) were positive to the Schistosoma-specific screen using real-time PCR methods. This study provides new insight into the recent changes in the epidemiology of urogenital schistosomiasis as likely driven by a new diversity of B. africanus group snails within the Lake.

Models for predicting bulinids species habitats in southwestern Nigeria

BackgroundSchistosomiasis prevalence is high in southwestern Nigeria and planorbids of the genus Bulinus had been implicated in the transmission of the disease in the area. The knowledge of species distribution in relation to environmental variables will be auspicious in planning control strategies. MethodsSatellite imagery and geographic information system (GIS) were used to develop models for predicting the habitats suitable for bulinid species. Monthly snail sample collection was done in twenty-three randomly selected water contact sites using the standard method for a period of two years. Remotely sensed variables such as Land Surface Temperature (LST), Normalized Difference Vegetation Index (NDVI) were extracted from Landsat TM, ETM+; Slope and Elevation were obtained from digital elevation model (DEM) while Rainfall was retrieved from European Meteorology Research Program. These environmental factors and snail species were integrated into QGIS to predict the potential habitats of different bulinid species using an exploratory regression model. ResultsThe following environmental variables: flat-moderate slope (0.01–15.83), LST (21.1 °C-23.4 °C), NDVI (0.19–0.52), rainfall (> 1569.34 mm) and elevation (1–278 m) contributed to the model used in predicting habitat suitable for bulinids snail intermediate hosts. Exploratory regression models showed that LST, NDVI and slope were predictors of Bulinus globosus and Bulinus jousseaumei; elevation, LST, rainfall and slope were predictors of Bulinus camerunensis; rainfall, NDVI and slope were predictors of B. senegalensis while NDVI and slope were predictors of Bulinus forskalii in the area. Bulinids in the forskalii group showed clustering in middle belt and south. The predictive risk map of B. jousseaumei was similar to the pattern described for B. globosus, but with a high R-square value of 81%. ConclusionThe predictive risk models of bulinid species in this study provided a robust output for the study area which could be used as base-line for other areas in that ecological zone. It will be useful in appropriate allocation of scarces resources in the control of schistosomiasis in that environment.

Evolution and Biogeography of Freshwater Snails of the Genus Bulinus (Gastropoda) in Afromontane Extreme Environments

Mountains are considered island-like systems often characterized by exceptional biodiversity and endemism. There are many highly isolated mountain ranges in Africa that collectively have been called the Afromontane archipelago. Freshwater snails of the genus Bulinus are composed of many veterinary and biomedical important species. These intermediate hosts for schistosomiasis parasites are wide spread and some of the species are considered to be highly adapted to very harsh environmental conditions such as droughts or low temperatures. However, the extent to which the Bulinus have adapted to live in high-altitudes and factors influencing these range shifts are not well investigated. In this study, we analyzed pan-African Bulinus species from various habitats across different altitudinal ranges, focusing on the high mountains or “sky islands” to examine how the contemporary climate and historical geological factors affect species distributions and evolutionary processes. Using a fossil-calibrated multigene phylogeny composed of two mitochondrial genes (cox1, 16S) and two nuclear genes (ITS2 and H3), we tested: 1) how often and when extreme altitudes were colonized, 2) what are the biogeographical affinities and degree of isolation of high-altitude species, 3) which lineages diversified and evolved endemism in the Afromontane environments, and 4) whether the Afromontane regions represent “sky islands”. Bayesian phylogenetic inference employing a fossil-calibrated molecular clock resulted in a strongly supported phylogeny resolving the relationships between the four Bulinus groups. High-altitude colonization exists exclusively within the Bulinus truncatus/tropicus complex. Several independent colonization events occurred in the Pliocene and Pleistocene throughout Africa, mostly from nearby regions of the respective mountain ranges. Most species evolved in low to mid-altitudinal ranges. Endemism is pronounced in the Ethiopian Highlands and those of Kenya and Lesotho. A previously unknown species was found at an extreme altitude (∼4,000 m a.s.l.) on Mt. Elgon/Uganda extending the formerly known altitudinal maximum of the genus by roughly 900 m. The endemic species has already diverged in the Pliocene (∼4 myr) and is currently characterized by low genetic diversity. There is further cryptic diversity in mountain ranges of Lesotho. Our findings are discussed in a biogeographical, conservation and biomedical context.

Comparative mitogenomics of freshwater snails of the genus Bulinus, obligatory vectors of Schistosoma haematobium, causative agent of human urogenital schistosomiasis

Among the snail genera most responsible for vectoring human-infecting schistosomes, Bulinus, Biomphalaria, and Oncomelania, the former is in many respects the most important. Bulinid snails host the most common human blood fluke, Schistosoma haematobium, responsible for approximately two-thirds of the estimated 237 million cases of schistosomiasis. They also support transmission of schistosomes to millions of domestic and wild animals. Nonetheless, our basic knowledge of the 37 Bulinus species remains incomplete, especially with respect to genome information, even including mitogenome sequences. We determined complete mitogenome sequences for Bulinus truncatus, B. nasutus, and B. ugandae, and three representatives of B. globosus from eastern, central, and western Kenya. A difference of the location of tRNA-Asp was found between mitogenomes from the three species of the Bulinus africanus group and B. truncatus. Phylogenetic analysis using partial cox1 sequences suggests that B. globosus is a complex comprised of multiple species. We also highlight the status of B. ugandae as a distinct species with unusual interactions with the S. haematobium group parasites deserving of additional investigation. We provide sequence data for potential development of genetic markers for specific or intraspecific Bulinus studies, help elucidate the relationships among Bulinus species, and suggest ways in which mitogenomes may help understand the complex interactions between Schistosoma and Bulinus snails and their relatives.

Characterization of freshwater snail intermediate hosts of schistosomes in four communities from Osun State, Southwest Nigeria

Aim: Freshwater snails of the genus Bulinus act as essential intermediate hosts of Schistosoma haematobium, a trematode parasite that causes urogenital schistosomiasis. The snails are widely distributed throughout Nigerian waters. Since species identification of the Bulinus snails is important for appropriate control strategies of urogenital schistosomiasis, this study therefore aimed at identifying the Bulinus species responsible for transmission of the infection in four communities located in an endemic Local Government Area of Nigeria. It also aimed at using restriction fragment length polymorphism (RFLP) as a more affordable method than sequencing to characterize Bulinus snails from schistosomiasis endemic regions in Nigeria. Methods: In this study, 100 freshwater snails morphologically identified as Bulinus species were collected from four communities located in a previously reported schistosomiasis endemic Local Government Area (LGA), namely Olorunda LGA in Oshun State, Southwest Nigeria. All snails were screened for schistosome infection using polymerase chain reaction (PCR) targeting the DraI gene. Molecular identification of the snails was done by PCR amplification of their entire internal transcribed spacer region including the 5.8S ribosomal RNA gene and RFLP. Results: Five of the 100 snails were positive for schistosome infection. PCR-RFLP profiles showed bands of different sizes for 26 other snails including the schistosome-infected ones. RFLP analysis showed that 11 of the snails belonged to the freshwater snails of the genus Physa while 13 belonged to the freshwater snails of the genus Bulinus, including Bulinus globosus (8) and B. truncatus (5). The species of the remaining two snails could not be resolved using the reference profiles from our previous studies. Conclusion: This study confirmed previous observations that limited morphological uniqueness within the Bulinus groups hinders their identification, and RFLP is a cheaper alternative method to sequencing that can be used by laboratories with limited resources for Bulinus species identification.

"Aqueous Extracts: An Alternative in the Control of the Intermediate Host of Schistosomiasis"

Schistosomiasis is a parasitic disease caused by worms of the genus Schistosoma. Some substances are used to control the intermediate host, being a strategy to prevent the risk of infection and re-infection of the disease. According to the WHO, the recommended substance is Niclosamide; however, it presents toxicity in non-target organisms. Aqueous extracts are being increasingly studied as a potential molluscicide in combating schistosomiasis. The aqueous extract of Moringa oleifera flowers was used to evaluate the molluscicidal activity in Biomphalaria glabrata. This extract caused lethality in adult molluscs, obtaining a lethal concentration 50 = 2.37 mg/mL. In the second aqueous extract, fruits of the species Randia nilotica were used on molluscs of the species Biomphalaria pfeifferi and Bulinus truncatus. These extracts showed molluscicidal activity on both molluscs used in the experiments. In the third aqueous extract, they used leaves of the species Anagallis arvensis to test the molluscicidal action on molluscs of the species Biomphalaria alexandrina. It was possible to obtain lethal concentrations, with lethal concentration 50 = 37.9 mg/L and lethal concentration 90 = 48.3 mg/L. In the fourth aqueous extract, they used the seeds of the species Moringa oleifera to evaluate the molluscicidal activity in molluscs of the genus Bulinus. These seeds showed molluscicidal action, but they were not in accordance with what is recommended by the WHO. According to the experiments carried out with aqueous extracts, it can be seen that there are many studies using these methodologies as a form of control for schistosomiasis. Some criteria are essential to obtain a low-cost aqueous extract. It is essential to emphasize that this methodology could be used by the government to control the intermediate host of schistosomiasis in less favored areas, where the population itself would have access to inputs using accessible technological resources.

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.

Immunology of Schistosomiasis

Background: Immunology studies include three main areas: infection, re-infection resistance to re-infection of schistosomiasis, and diagnosis. Objective: In this study, the author reports a study of immunology of schistosomiasis that focused on some important issues include mammalian host, important species of schistosomes, life cycle, host’s immune response, and diagnosis as objectives of this study. Methodology: The author searched Google, Science Direct and the PubMed Database of NCBI for articles on immunology of schistotomiasis published between 2009 and 2021. Articles were unrestricted open access, articles with permissions from Elsevier if required, and in English. Other relevant publications were also included. Results: Commonly, three Schistosoma species can infect humans. These include Schistosoma haematobium, Schistosoma japonicum, and Schistosoma mansoni. Schistosoma haematobium can infect such as baboons, humans, monkeys, and rhesus monkey. Schistosoma japonicum can infect such as humans, buffalos, dogs, and wild pigs. Schistosoma mansoni can infect humans and wild primates. The genus Schistosoma has two hosts: intermediate hosts and definite hosts. Intermediate hosts of S. haematobium, S. japonicum, and S. mansoni are the genus Bulinus, genus Oncomelania and genus Biomphalaria, respectively. In humans, cercariae released by intermediate hosts reach, and penetrate human skin. When cercariae reach human, it induce type 1 (Th1) immune responses and elevates such as IL-12 and TNFα. With worms reach adults, it induces Th2 immune response and elevates such as IL-4 and IL-13, and cause Th1 decrease. Increase of Th2 causes the development of hepatic granulomatous and fibrosis. Treatment can decrease Th2 and significantly hepatic granulomatous formation and fibrosis. In addition, it can reduce schistosomiasis cases. However, re-infection can occur in people who live in endemic areas. For diagnosing schistosomiasis, there are several tools can be used. These include such as microscopic and molecular tools. Conclusion: Th1 immune responses elevate serum cytokine levels such as IL-12 and TNFα. When Th1 is decreased, it elevates Th2 immune responses and level of cytokines such as IL-4 and TGF-β. This causes the development of granulomatous and fibrosis, even diseases such as cancer. Re-infection of schistomiasis can occur in people that have been treated, especially in the endemic areas. Tools for detecting schistosomiasis infection can include such as microscope and molecular methods.

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

BackgroundThe 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.MethodsSequences 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.ResultsPhylogenies, 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.ConclusionsThe 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.

First report of extraordinary corkscrew gastropods of the genus Bulinus in Lake Malawi

Open-coiled shells are rarely observed in gastropods, but they may occur at a relative frequency ranging from a small percentage of specimens in a population up to being specific to populations or even species. The origin of such corkscrew-like shells are poorly understood, but may include developmental anomalies, ecophenotypic plasticity or genetic inheritance. Here, we report the first case of gastropods from Lake Malawi with corkscrew-like shells, and we use comparative molecular studies with two mitochondrial gene fragments (COI and 16S rRNA) to examine its origin. The specimens belong to the genus Bulinus, more specifically to one of five clades of Bulinus recovered from the Malawi Basin. Beyond being seemingly specific to one of these Bulinus clades, network analyses indicate low genetic differentiation from the other, regularly shaped specimens in this clade. Although our results do not fully discard the possibility of corkscrew-like shells being genetically inherited or being caused by growth disturbance, their restrictive occurrence in a few geographically isolated populations in sympatry with specimens displaying a regular shell shape supports the hypothesis that the corkscrew-like shell shape in Bulinus is caused by ecophenotypic plasticity. For now, it is unclear whether aspects of the physical environment, or biotic interactions, such as a release from predation, caused the corkscrew-like morphotype. The phenomenon may have been caused by the multiple environmental changes that Lake Malawi has been undergoing over recent decades.

Prevalence of Urinary Schistosomiasis among School Aged Children in Bakura Local Government Area of Zamfara State Nigeria

Urinary schistosomiasis (Bilharziasis) is a parasitic disease caused by digenic trematode called Schistosoma haematobium, it is a water based parasitic disease transmitted by water snails of the genus Bulinus that mainly affect children. A study was carried out to determine the prevalence of Urinary Schistosomiasis among School aged children of three selected communities in Bakura LGA of Zamfara State to determine the prevalence of S. haematobium from urine samples of the pupils and to relate the prevalence of infection with socio- demographic factors such as age, sex and water contact activities of the sampled subject. A total of 360 urine samples comprising of 120 each from the Yargeda, Kwanar Kalgo and Tungar Maiburtu Primary Schools were collected and examined by sedimentation technique for the presence of S. haematobium eggs. The overall percentage of infection recorded was 30.0% while percentages of infection obtained among the selected Primary Schools were 33.3%, 16.7% and 40.0% in Yargeda, Kwanar Kalgo and Tungar Maiburtu respectively. Male pupils recorded the highest rate of infection (44.9%) than female pupils (23.6%). Age group 8-11 years old had highest infection rate (35.7%), while the age group 12-15 years had the least prevalence rate (23.5%). In relation to sources of drinking water, pupils with rivers/streams as their main sources of drinking water recorded the highest rate of infection (38.7%), whereas those using tap/bore-hole water had the least prevalence of infection (18.2%). Based on water contact activity, pupils whose water contact activity was mostly fishing had the highest rate (41.4%), while lowest rate of infection of 18.0% was observed among pupils swimming in rivers. In all the cases, chi-square analysis showed no significant association between the rate of infection and water contact activities (P<0.01). Since infection with S. haematobium had been established in the study area, there is therefore a need for public health campaign among pupils to adapt preventive measures with control programs for snails’ intermediate host.

Amphistome infections in domestic and wild ruminants in East and Southern Africa: A review.

In this article, the main amphistome species infecting domestic and wild ruminants in East and Southern Africa, their snail intermediate hosts and epidemiological features are reviewed and discussed. Twenty-six amphistome species belonging to nine genera from three families occur in domestic and wild ruminants in the region under review and over 70% of them belong to the genera Calicophoron, Carmyerius and Cotylophoron. Of the amphistome species, 76.9% are shared between domestic and wild ruminant hosts – an important observation when considering the different options for control. Seven freshwater snail species belonging to four genera from two families act as intermediate hosts of the identified amphistome species, with the genus Bulinus contributing 57% of the snail species. Some of the snails are intermediate hosts of amphistome species belonging to the same genus or to different genera; a phenomenon not yet fully elucidated as some snails are reported to be naturally infected with amphistome cercariae of unidentified species. Only nine (34.6%, 9/26) of the amphistome species have known snail intermediate hosts, while most (65.4%, 17/26) have unknown hosts. Species of intermediate hosts and the potential of the flukes to infect these hosts, the biological potential of the snail hosts, the definitive hosts management systems and their grazing habits are considered to be the main factors influencing the epidemiology of amphistomosis. Based on the epidemiological features of amphistome infections, various practical control options are discussed. Further research is necessary to determine amphistome–snail associations, develop diagnostic tests that can detect prepatent infections in the definitive host, determine the burden and economic importance of amphistomosis in domestic and wild ruminants and the efficacy of different anthelmintics in the treatment of patent infections.

The substructure of three repetitive DNA regions of Schistosoma haematobium group species as a potential marker for species recognition and interbreeding detection

BackgroundSchistosoma haematobium is the causative agent of human urogenital schistosomiasis affecting ~112 million people in Africa and the Middle East. The parasite is transmitted by snails of the genus Bulinus, which also transmit other closely related human and animal schistosomes. The accurate discrimination of S. haematobium from species infecting animals will aid effective control and elimination programs. Previously we have shown the utility of different repetitive nuclear DNA sequences (DraI, sh73bp, and sh77bp) for the identification of S. haematobium-group species and inter-repeat sequences for discriminating S. haematobium from S. bovis.ResultsIn this current study we clarify the structural arrangement and association between the three repetitive sequences (DraI, sh73bp, and sh77bp) in both S. haematobium and S. bovis, with a unique repeat linker being found in S. haematobium (Sh64bp repeat linker) and in S. bovis (Sb30bp repeat linker). Sequence data showed that the 3′-end of the repeat linker was connected to the DraI repetitive sequence array, and at the 5′-end of the repeat linker sh73bp and sh77bp were arranged in an alternating manner. Species-specific oligonucleotides were designed targeting the species-specific repeat linkers and used in a reverse line blot (RLB) hybridization assay enabling differentiation between S. haematobium and S. bovis. The assay was used to discriminate natural infections in wild caught Bulinus globosus.ConclusionThis research enabled the characterisation of species-specific DNA regions that enabled the design of species-specific oligonucleotides that can be used to rapidly differentiate between S. haematobium and S. bovis and also have the potential to aid the detection of natural hybridization between these two species.

The Schistosoma indicum species group in Nepal: presence of a new lineage of schistosome and use of the Indoplanorbis exustus species complex of snail hosts

From 2007–2014, 19,360 freshwater snails from the Terai and Hilly regions of Nepal were screened for cercariae of mammalian schistosomes. Based on analysis of mitochondrial cytochrome oxidase I, 12S, 16S and 28S sequences (3,675bp) of the cercariae recovered, we provide, to our knowledge, the first report of the Schistosoma indicum species group in Nepal. Five samples of Schistosoma nasale, nine of Schistosoma spindale and 17 of Schistosoma sp. were recovered, all from the snail Indoplanorbis exustus. The last-mentioned lineage failed to group in any of our analyses with S. nasale, S. spindale or S. indicum. It diverged in cox1 sequence from them by 16%, 13% and 13%, respectively, levels of difference comparable to well-studied species pairs of Schistosoma. Analysis of cox1, 16S and internal transcribed spacer 1 sequences (1,874bp) for Nepalese specimens of I. exustus was also surprising in revealing the presence of four genetically distinct clades. They diverged from one another at levels comparable to those noted for species pairs in the sister genus Bulinus. There was no obvious pattern of use by Nepalese Schistosoma of the Indoplanorbis clades. We found high support for a close relationship between S. indicum and Schistosoma haematobium groups, but failed to retrieve support for a clean separation of the two, with a tendency for S. nasale to fall as the most basal representative. If this pattern holds, hypotheses for the origin of the Asian Indoplanorbis-transmitted S. indicum group from the Bulinus-transmitted S. haematobium group may require modification, including consideration of more contemporaneous origins of the two groups. The Indian subcontinent is under-studied with respect to schistosome diversity and our current knowledge of the S. indicum and I. exustus species groups is inadequate. Further study is warranted given the ability of indicum group species to cause veterinary problems and cercarial dermatitis, with a worrisome potential in the future to establish infections in humans.

Molecular characterisation of Bulinus snails – intermediate hosts of schistosomes in Ogun State, South-western Nigeria

Freshwater snails of the genus Bulinus O. F. Muller, 1781 are intermediate hosts for schistosomes, trematode parasites which cause schistosomiasis. The genus includes closely related species complexes with restricted gene flow between populations of each taxon. Despite their importance as intermediate hosts, unambiguous identification of these snails remains challenging. We applied molecular approach to their identification to achieve a better understanding of the epidemiology of schistosomiasis in an endemic region, south-western Nigeria. A total of 149 snails were collected and their genomic DNA was screened for schistosome infection using PCR amplification of schistosome DraI repeat sequence. The snails were identified by PCR-RFLP and/or sequencing of an amplicon of their entire ITS region including the 5.8S ribosomal RNA (rRNA) gene. Four Bulinus species, namely B. globosus (Morelet, 1866), B. forskalii (Ehrenberg, 1831), B. camerunensis Mandahl-Barth, 1957 and B. senegalensis O. F. Muller, 1781 were identified, and 34.9% (n = 52) of the 149 snails were infected: B. globosus 25.5% (n = 38), B. forskalii 5.4% (n = 8), B. camerunensis 2.7% (n = 4) and B. senegalensis 1.3% (n = 2). Restriction fragment profiles of the ribosomal ITS region for B. globosus closely matched those obtained in our previous study thus confirming the view that ribosomal ITS region of these snails could be well suited for taxonomic studies. The use of sequencing for species identification was costly and time-consuming, but it was effective in resolving true identities of snails whose restriction profiles were similar and inconclusive. key wOrds: species identification, Bulinus, ITS, rRNA gene, schistosome, schistosomiasis, Nigeria

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

BackgroundSnails 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).ResultsThe 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.ConclusionThe 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.

The ITS2 of the genus Bulinus: Novel secondary structure among freshwater snails and potential new taxonomic markers

The freshwater snail genus Bulinus has been intensively investigated due to its role as intermediate host for trematode blood flukes that cause the debilitating disease schistosomiasis in man and livestock. Owing to taxonomic ambiguities within Bulinus, attention has often focused upon species delineation and several molecular methods have recently been used for identification and characterization purposes. Inspection of compensatory base changes (CBCs) in the secondary structure of the nuclear ribosomal internal transcribed spacer (ITS) has been used to differentiate species in other genera, and here we present a study investigating the presence of CBCs between species in the species groups within Bulinus. CBCs were present within B. forskalii and B. globosus indicating that these widely distributed taxa might constitute cryptic species complexes. However, other currently recognized species could not be distinguished by CBC analysis. The putative secondary structure of the very long ITS2 sequence of the B. reticulatus species group had an additional helix (DIIa) between DII and DIII not seen in other species groups of Bulinus. The accumulation and inspection of further ITS2 sequences will no doubt reveal additional variation between Bulinus populations, and CBCs should be incorporated in future taxonomic work in this group.