Population genetics of African Schistosoma species.

Blood flukes within the genus Schistosoma (schistosomes) are responsible for the major disease, schistosomiasis, in tropical and sub-tropical areas. This disease is predominantly present on the African continent with more than 85% of the human cases. Schistosomes are also parasites of veterinary importance infecting livestock and wildlife. Schistosoma population genetic structure and diversity are important characteristics that may reflect variations in selection pressures such as those induced by host (mammalian and snail) environments, habitat change, migration and also treatment/control interventions, all of which also shape speciation and evolution of the whole Schistosoma genus. Investigations into schistosome population genetic structure, diversity and evolution has been an area of important debate and research. Supported by advances in molecular techniques with capabilities for multi-locus genetic analyses for single larvae schistosome genetic investigations have greatly progressed in the last decade. This paper aims to review the genetic studies of both animal and human infecting schistosome. Population genetic structures are reviewed at different spatial scales: local, regional or continental (i.e. phylogeography). Within species genetic diversities are discussed compared and the compounding factors discussed, including the effect of mass drug administration. Finally, the ability for intra-species hybridisation questions species integrities and poses many questions in relation to the natural epidemiology of co-endemic species. Here we review molecularly confirmed hybridisation events (in relation to human disease) and discuss the possible impact for ongoing and future control and elimination.

Advancing the multi-disciplinarity of parasitology within the British Society for Parasitology: studies of host-parasite evolution in an ever-changing world.

The study of parasites typically crosses into other research disciplines and spans across diverse scales, from molecular- to populational-levels, notwithstanding promoting an understanding of parasites set within evolutionary time. Today, the 2030 Sustainable Development Goals (SDGs) help frame much of contemporary parasitological research, since parasites can be found in all ecosystems, blighting human, animal and plant health. In recognition of the multi-disciplinary nature of parasitological research, the 2017 Autumn Symposium of the British Society for Parasitology was held in London to provide a forum for novel exchange across medical, veterinary and wildlife fields of study. Whilst the meeting was devoted to the topic of parasitism, it sought to foster mutualism, the antithesis perhaps of parasitism, by forging new academic connections and social networks to exchange novel ideas. The meeting also celebrated the longstanding career of Professor David Rollinson, FLS in the award of the International Federation for Tropical Medicine Medal for his efforts spanning 40 years of parasitological research. Indeed, David has done so much to explore and promote the fascinating biology of parasitism, as exemplified by the 15 manuscripts contained within this Special Issue.

The Establishment and Function of Schistosomiasis Surveillance System Towards Elimination in The People's Republic of China.

Schistosoma japonicum is the main schistosome species in The People's Republic of China, causing intestinal schistosomiasis, a debilitating disease of public health importance. The People's Republic of China used to be heavily endemic with schistosomiasis, but great progress has been made through the vigorous efforts of the national control programmes in the last six decades. Presently, efforts are geared towards eliminating schistosomiasis from The People's Republic of China by the end of 2025 through effective schistosomiasis surveillance, an important component in the drive towards schistosomiasis elimination. Therefore, this article explicitly outlines the development and progress made in schistosomiasis surveillance since 1990 with a special focus on the new surveillance system in use. Although the surveillance system has steadily improved over the years, it is faced with many challenges. Hence, more efforts are needed to establish an effective and sensitive evaluation system for the national schistosomiasis elimination programme in The People's Republic of China.

Erratum to: Development of novel multiplex microsatellite polymerase chain reactions to enable high-throughput population genetic studies of Schistosoma haematobium.

Unfortunately, the original version of this article [1], contained a mistake. In Table 1, the primers for Sh6 and Sh9 were included incorrectly. Instead of GGGATGTATGCAGACTTG TTGTTTGGCTGCAGTAAC and GCTGAGCTTGAGATTG CTTCTGTCCCATCGATACC they should have been Sh6 Forward Primer GGTGGATTACGCAATAG, Sh6 Reverse Primer TTTAATCAACCGGGTGTC and Sh9 Forward Primer GGGATGTATGCAGACTTG, Sh9 Reverse Primer TTGTTTGGCTGCAGTAAC respectively. A corrected version of Table 1 is included below

Isothermal Recombinase Polymerase amplification (RPA) of Schistosoma haematobium DNA and oligochromatographic lateral flow detection.

BACKGROUND: Accurate diagnosis of urogenital schistosomiasis is vital for surveillance/control programs. Amplification of schistosome DNA in urine by PCR is sensitive and specific but requires infrastructure, financial resources and skilled personnel, often not available in endemic areas. Recombinase Polymerase Amplification (RPA) is an isothermal DNA amplification/detection technology that is simple, rapid, portable and needs few resources. FINDINGS: Here a Schistosoma haematobium RPA assay was developed and adapted so that DNA amplicons could be detected using oligochromatographic Lateral Flow (LF) strips. The assay successfully amplified S. haematobium DNA at 30-45 °C in 10 mins and was sensitive to a lower limit of 100 fg of DNA. The assay was also successful with the addition of crude urine, up to 5% of the total reaction volume. Cross amplification occurred with other schistosome species but not with other common urine microorganisms. CONCLUSION: The LF-RPA assay developed here can amplify and detect low levels of S. haematobium DNA. Reactions are rapid, require low temperatures and positive reactions are interpreted using lateral flow strips, reducing the need for infrastructure and resources. This together with an ability to withstand inhibitors within urine makes RPA a promising technology for further development as a molecular diagnostic tool for urogenital schistosomiasis.

Development of novel multiplex microsatellite polymerase chain reactions to enable high-throughput population genetic studies of Schistosoma haematobium.

BACKGROUND: Human urogenital schistosomiasis caused by Schistosoma haematobium is widely distributed across Africa and is increasingly targeted for control and regional elimination. The development of new high-throughput, cost-effective molecular tools and approaches are needed to monitor and evaluate the impact of control programs on the parasite populations. Microsatellite loci are genetic markers that can be used to investigate how parasite populations change over time and in relation to external influences such as control interventions. FINDINGS: Here, 18 existing S. haematobium microsatellite loci were optimised to enable simultaneous amplification across two novel multiplex microsatellite PCR's, each containing nine loci. Methods were developed for the cost effective and rapid processing and microsatellite analysis of S. haematobium larval stages stored on Whatman-FTA cards and proved robust on miracidia and cercariae collected from Zanzibar and Niger. CONCLUSION: The development of these novel and robust multiplex microsatellite assays, in combination with an improved protocol to elute gDNA from Whatman-FTA fixed schistosome larval stages, enables the high-throughput population genetic analysis of S. haematobium. The molecular resources and protocols described here advance the way researchers can perform multi locus-based population genetic analyses of S. haematobium as part of the evaluation and monitoring of schistosomiasis control programmes.

Regular treatments of praziquantel do not impact on the genetic make-up of Schistosoma mansoni in Northern Senegal.

The Senegal River Basin (SRB) experienced a major epidemic of intestinal schistosomiasis in the early nineties, after the construction of a dam for irrigation purposes. Exceptionally low cure rates following praziquantel (PZQ) treatment at the onset of the epidemic raised concerns about PZQ resistant strains of Schistosoma mansoni, although they could also be attributed to the intense transmission at that time. A field study in the same region more than 15 years later found cure rates for S. mansoni still to be low, whereas Schistosomahaematobium responded well to treatment. We collected S. mansoni miracidia from children at base-line prior to treatment, six months after two PZQ treatments and two years after the start of the study when they had received a total of five PZQ treatments. In total, 434 miracidia from 12 children were successfully genotyped with at least six out of nine DNA microsatellite loci. We found no significant differences in the genetic diversity of, and genetic differentiation between parasite populations before and after repeated treatment, suggesting that PZQ treatment does not have an impact on the neutral evolution of the parasite. This is in stark contrast with a similar study in Tanzania where a significant decrease in genetic diversity was observed in S. mansoni miracidia after a single round of PZQ treatment. We argue that PZQ resistance might play a role in our study area, although rapid re-infection cannot be excluded. It is important to monitor this situation carefully and conduct larger field studies with short-term follow-up after treatment. Since PZQ is the only general schistosomicide available, the possibility of PZQ resistance is of great concern both for disease control and for curative use in clinical practice.

Adding resolution to ordinal level relationships of tapeworms (Platyhelminthes: Cestoda) with large fragments of mtDNA.

The construction of a stable phylogeny for the Cestoda, indicating the interrelationships of recognised orders and other major lineages, has proceeded iteratively since the group first received attention from phylogenetic systematists. Molecular analyses using nuclear ribosomal RNA gene fragments from the small (ssrDNA) and large (lsrDNA) subunits have been used to test competing evolutionary scenarios based on morphological data but could not arbitrate between some key conflicting hypotheses. To the ribosomal data, we have added a contiguous fragment of mitochondrial (mt) genome data (mtDNA) of partial nad1-trnN-trnP-trnI-trnK-nad3-trnS-trnW-cox1-trnT-rrnL-trnC-partial rrnS, spanning 4034-4447 bp, where new data for this region were generated for 18 species. Bayesian analysis of mtDNA and rDNA as nucleotides, and where appropriate as amino acids, demonstrated that these two classes of genes provide complementary signal across the phylogeny. In all analyses, except when using mt amino acids only, the Gyrocotylidea is sister group to all other Cestoda (Nephroposticophora), and Amphilinidea forms the sister group to the Eucestoda. However, an earliest-diverging position of Amphilinidea is strongly supported in the mt amino acid analysis. Amphilinidea exhibit a unique tRNA arrangement (nad1-trnI-trnL2-trnP-trnK-trnV-trnA-trnN-nad3), whereas Gyrocotylidea shares that of the derived lineages, providing additional evidence of the uniqueness of amphilinid genes and genomes. The addition of mtDNA to the rDNA genes supported the Caryophyllidea as the sister group to (Spathebothriidea+remaining Eucestoda), a hypothesis consistently supported by morphology. This relationship suggests a history of step-wise evolutionary transitions from simple monozoic, unsegmented tapeworms to the more familiar polyzoic, externally segmented (strobilate) forms. All our data partitions recovered Haplobothriidea as the sister group to Diphyllobothriidae. The sister-group relationship between Diphyllidea and Trypanorhyncha, as previously established using rDNA, is not supported by the mt data, although it is supported by the combined mt and rDNA analysis. With regards to the more derived taxa, in all except the mt amino acid analysis, the following topology is supported: (Bothriocephalidea (Litobothriidea (Lecanicephalidea (Rhinebothriidea (Tetraphyllidea, (Acanthobothrium, Proteocephalidea), (Nippotaeniidea, Mesocestoididae, Tetrabothriidea, Cyclophyllidea)))))), where the Tetraphyllidea are paraphyletic. Evidence from the mt data provides strong (nucleotides) to moderate (amino acids) support for Tetraphyllidea forming a group to the inclusion of Proteocephalidea, with the latter consistently forming the sister group to Acanthobothrium. The interrelationships among Nippotaeniidea, Mesocestoididae, Tetrabothriidea and Cyclophyllidea remain ambiguous and require further systematic attention. Mitochondrial and nuclear rDNA data provide conflicting signal for certain parts of the cestode tree. In some cases mt data offer results in line with morphological evidence, such as the interrelationships of the early divergent lineages. Also, Tetraphyllidea, although remaining paraphyletic with the inclusion of the Proteocephalidea, does not include the most derived cestodes; a result which has consistently been obtained with rDNA.

Rapid diagnostic multiplex PCR (RD-PCR) to discriminate Schistosoma haematobium and S. bovis.

Schistosoma haematobium and S. bovis are widespread schistosome species causing human and cattle schistosomiasis, respectively, in Africa. The sympatric occurrence of these two species and their ability to infect the same Bulinus intermediate snail hosts necessitates precise methods of identification of the larval stages. A rapid diagnostic 'mulitplex' one-step polymerase chain reaction protocol (RD-PCR) was developed using cytochrome oxidase subunit 1 (COX1) mitochondrial DNA (mtDNA) to discriminate between S. haematobium and S. bovis. A single forward primer and two species-specific reverse primers were used to produce a polymerase chain reaction (PCR) fragment of 306 bp and 543 bp for S. bovis and S. haematobium, respectively. Serial dilutions were carried out on various lifecycle stages and species combinations to test the sensitivity and specificity of the primers. This RD-PCR proved highly sensitive, detecting a single larval stage and as little as 0.78 ng of genomic DNA (gDNA) from an adult schistosome, providing a cost-effective, rapid and robust molecular tool for high-throughput screening of S. haematobium and S. bovis populations. In areas where human and cattle schistosomiasis overlap and are transmitted in close proximity, this mitochondrial assay will be a valuable identification tool for epidemiological studies, especially when used in conjunction with other nuclear diagnostic markers.

Molecular epidemiology of Schistosoma mansoni in Uganda: DNA barcoding reveals substantial genetic diversity within Lake Albert and Lake Victoria populations.

Representative samples of Ugandan Schistosoma mansoni from Lake Albert and Lake Victoria were examined using DNA barcoding, sequence analysis of two partially overlapping regions - ASMIT (396 bp) & MORGAN (617 bp) - of the mitochondrial cytochrome oxidase subunit I (cox1). The Victorian sample exhibited greater nucleotide diversity, 1.4% vs. 1.0%, and a significant population partition appeared as barcodes did not cross-over between lakes. With one exception, Lake Albert populations were more mixed by sampled location, while those from Lake Victoria appeared more secluded. Using statistical parsimony, barcode ASMIT 1 was putatively ancestral to all others and analysis of MORGAN cox1 confirmed population diversity. All samples fell into two of five well-resolved lineages; sub-lineages therein broadly partitioning by lake. It seems that barcode ASMIT 1 (and close variants) was likely widely dispersed throughout the Nilotic environment but later diversified in situ, and in parallel, within Lake Albert and Lake Victoria. The genetic uniformity of Ugandan S. mansoni can no longer be assumed, which might better explain known epidemiological heterogeneities. While it appears plausible that locally evolved heritable traits could spread through most of the Lake Albert populations, it seems unlikely they could quickly homogenise into Lake Victoria or amongst populations therein.

The mitochondrial genome of Gyrodactylus salaris (Platyhelminthes: Monogenea), a pathogen of Atlantic salmon (Salmo salar).

In the present study, we describe the complete mitochondrial (mt) genome of the Atlantic salmon parasite Gyrodactylus salaris, the first for any monogenean species. The circular genome is 14,790 bp in size. All of the 35 genes recognized from other flatworm mitochondrial genomes were identified, and they are transcribed from the same strand. The protein-coding and ribosomal RNA (rRNA) genes share the same gene arrangement as those published previously for neodermatan mt genomes (representing cestodes and digeneans only), and the genome has an overall A+T content of 65%. Three transfer RNA (tRNA) genes overlap with other genes, whereas the secondary structure of 3 tRNA genes lack the DHU arm and 1 tRNA gene lacks the TphiC arm. Eighteen regions of non-coding DNA ranging from 4 to 112 bp in length, totalling 278 bp, were identified as well as 2 large non-coding regions (799 bp and 768 bp) that were almost identical to each other. The completion of the mt genome offers the opportunity of defining new molecular markers for studying evolutionary relationships within and among gyrodactylid species.

A single-strand conformation polymorphism (SSCP) approach for investigating genetic interactions of Schistosoma haematobium and Schistosoma guineensis in Loum, Cameroon.

Single-strand conformation polymorphism (SSCP) analysis of the second internal transcribed spacer (ITS2) of nuclear ribosomal DNA provides a molecular tool for the identification of Schistosoma haematobium, Schistosoma guineensis and the hybrids of these two species. This molecular tool was utilized to provide a detailed analysis of the interactions between S. haematobium and S. guineensis in hybrid zones of Loum, Littoral Province, Cameroon. Individual hybrid schistosomes were identified within the natural populations collected from Loum in 1990, 1999 and 2000, which would have been misidentified as S. haematobium using solely morphological and sequence criteria. This study indicates the complexities of the hybridization between S. haematobium and S. guineensis and emphasizes the importance of assessing morphological, biological and molecular data to gain insights into the interaction of these two species over time.

Development and application of an ethically and epidemiologically advantageous assay for the multi-locus microsatellite analysis of Schistosoma mansoni.

Non-availability of adult worms from living hosts remains a key problem in population genetic studies of schistosomes. Indirect sampling involving passage through laboratory animals presents significant ethical and practical drawbacks, and may result in sampling biases such as bottlenecking processes and/or host-induced selection pressures. The novel techniques reported here for sampling, storage and multi-locus microsatellite analysis of larval Schistosoma mansoni, allowing genotyping of up to 7 microsatellite loci from a single larva, circumvent these problems. The utility of these assays and the potential problems of laboratory passage, were evaluated using 7 S. mansoni population isolates collected from school-children in the Hoima district of Uganda, by comparing the associated field-collected miracidia with adult worms and miracidia obtained from a single generation in laboratory mice. Analyses of laboratory-passaged material erroneously indicated the presence of geographical structuring in the population, emphasizing the dangers of indirect sampling for population genetic studies. Bottlenecking and/or other sampling effects were demonstrated by reduced variability of adult worms compared to their parent field-collected larval samples. Patterns of heterozygote deficiency were apparent in the field-collected samples, which were not evident in laboratory-derived samples, potentially indicative of heterozygote advantage in establishment within laboratory hosts. Genetic distance between life-cycle stages in the majority of isolates revealed that adult worms and laboratory-passaged miracidia clustered together whilst segregating from field miracidia, thereby further highlighting the utility of this assay.

Robinia aurata n. g., n. sp. (Digenea: Hemiuridae) from the mugilid Liza aurata with a molecular confirmation of its position within the Hemiuroidea.

Robinia aurata n. g., n. sp. is described from Liza aurata (Mugilidae), the golden grey mullet, from the Ebro Delta, Spanish Mediterranean. The new genus differs from all other hemiurid genera in the combined possession of muscular flanges and a vestigial ecsoma. Within the Bunocotylinae, which currently accommodates 2 genera, Bunocotyle and Saturnius, the new genus exhibits a unique combination of blind caeca, Juel's organ, post-ovarian bulk of the uterus in the hind-body, and tegumental papillae surrounding the oral and ventral sucker apertures. Furthermore, Robinia n. g. differs from both Bunocotyle and Saturnius in the nature of the muscular extensions around the oral sucker, with the shape of a muscular belt in the latter and numerous muscular papillae in the former. The phylogenetic hypothesis for the Bunocotylinae developed from sequence data analyses based on partial lsrDNA and complete ssrDNA combined (22 species) and V4 domain of the ssrRNA gene (37 species) supports the erection of the new genus and confirms its position within the Hemiuroidea. Both molecular analyses confirmed the monophyly of the Hemiuroidea, its division into 2 major clades and the polyphyly of the Derogenidae, as in previous studies, and suggest that the Gonocercinae (with 2 genera, Gonocerca and Hemipera), may require a distinct familial status. Finally, there was poor support for the distinct status of the Lecithasteridae and Hemiuridae, following previous suggestions based on different sequence data sets. A key to genera of the Bunocotylinae is presented.

The interaction of Schistosoma haematobium and S. guineensis in Cameroon.

Interactions between schistosomes are complex with some different species being able to mate and hybridize. The epidemiology of schistosomiasis in specific areas of South West Cameroon has evolved remarkably over 30 years as a result of hybridization between Schistosoma guineensis and S. haematobium. Morphological and biological data suggest that S. haematobium replaced S. guineensis in areas of Cameroon through introgressive hybridization. Data are reported on the use of single stranded conformational polymorphism (SSCP) analysis of the nuclear ribosomal second internal transcribed spacer (ITS2) of individual schistosomes from hybrid zones of Cameroon. The data show that since 1990 S. haematobium has completely replaced S. guineensis in Loum, with S. haematobium and the recombinants still present in 2000. This study illustrates the complexities of the dynamics between S. haematobium and S. guineensis in South West Cameroon.

Compatibility of Schistosoma haematobium, S. intercalatum and their hybrids with Bulinus truncatus and B. forskalii.

Schistosoma haematobium and S. intercalatum readily hybridize with each other producing generations of viable hybrid offspring. Experiments were designed to investigate the infectivity and viability of the S. haematobium x S. intercalatum F1 and F2 hybrid larvae in their two intermediate snail hosts compared with the parental species. Analysis of the data obtained suggested that the S. haematobium male x S. intercalatum female F1 hybrid miracidia were more infective to Bulinus truncatus than to B.forskalii, and also more infective to B. truncatus compared with the parental S. haematobium miracidia. This hybrid was also observed to have a greater cercarial productivity from both intermediate hosts and these cercariae were shown to be more infectious and to have a longer longevity compared with the cercariae of S. haematobium, S. intercalatum and the S. haematobium female x S. intercalatum male F1 hybrid cercariae. The S. haematobium female x S. intercalatum male F1 hybrid was shown not to be very successful in all stages of the investigations. The results indicate that the S. haematobium male x S. intercalatum female F1 hybrid may have many reproductive advantages over the reciprocal hybrid and the parental schistosome species. The significance of the results is discussed in relation to the epidemiological consequences occurring in Loum, Cameroon, and other areas where S. haematobium and S. intercalatum are sympatric and able to hybridize.

Isoenzyme analysis of Schistosoma haematobium, S. intercalatum and their hybrids and occurrences of natural hybridization in Cameroon.

Isoelectric focusing of glucose-6-phosphate dehydrogenase (G6PD) produced clearly identifiable profiles for S. haematobium and S. intercalatum and their hybrids. To provide a more detailed analysis of the interactions of S. haematobium and S. intercalatum in South West Cameroon over the last 12 years, G6PD analyses were carried out on individual schistosomes collected in Kumba in 1990, Loum in 1990, 1999 and 2000 and Barombi Mbo and Barombi Kotto in 1999. Studies were also carried out on the two parental species S. haematobium Barombi Mbo, S. intercalatum Edea and subsequent generations of hybrids resulting from laboratory crosses of the two parental species. The isoenzyme analysis demonstrated that the 1990 isolate from Kumba, was a recombinant of S. intercalatum x S. haematobium, and that 30% of individual schistosomes collected in 1990 in Loum were also recombinants. The remainder gave data indicative of S. haematobium. In 1999, 12.5% of individuals from Loum showed recombination and 10% in 2000. Results from the most recent parasitological survey in October 2000 showed the persistence of the recombinant population in addition to that of S. haematobium. There was also evidence of recombination having taken place in Barombi Kotto but not Barombi Mbo. This study demonstrates how the situation has changed over the last 12 years, and emphasizes the importance of assessing morphological, biological and molecular data together to gain a true picture of the rapidly evolving situation.

Mating interactions of Schistosoma haematobium and S. intercalatum with their hybrid offspring.

Experiments were designed to study the mating behaviour between the Schistosoma haematobium male x S. intercalatumfemale hybrid and the 2 parental species S. haematobium and S. intercalatum. Individual worms were identified by electrophoretic analysis of glucose-6-phosphate dehydrogenase, which was characteristic for each isolate. Analysis of the data obtained showed that both heterospecific and homospecific pairs formed between the hybrids and S. haematobium and S. intercalatum. S. haematobium and the hybrid are better than S. intercalatum in forming pairs, and S. haematobium showed a greater homospecific mate preference compared with the hybrid. Analysis of the data using the Mantel-Haenszel test suggests that mating competition does exist between the schistosomes, with the hybrid being dominant over both the parental species and S. haematobium being dominant over S. intercalatum. The hybrid males showed a greater ability than S. intercalatum and S. haematobium males in taking away S. haematobium and S. intercalatum females from their homospecific males when introduced into a pre-established S. haematobium or S. intercalatum infection. They were able to take females from S. intercalatum homospecific pairs more easily compared with females from S. haematobium homospecific pairs. The significance of the results is discussed in relation to the epidemiological changes of schistosomiasis in Cameroon, where hybridization between S. haematobium and S. intercalatum has taken place, with S. haematobium and the hybrid managing to replace the endemic S. intercalatum over the last 30 years.

Studies on the biology of schistosomiasis with emphasis on the Senegal river basin.

The construction of the Diama dam on the Senegal river, the Manantali dam on the Bafing river, Mali and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni in Northern Senegal, associated with high intensity of infections, due to intense transmission, and the creation of new foci of S. haematobium. Data on the vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard Toll, Senegal are presented with sympatric and allopatric (Cameroon) S. mansoni. Comparisons are made on infectivity, cercarial production, chronobiology of cercarial emergence and longevity of infected snails. Recent data on the intermediate host specificity of different isolates of S. haematobium from the Lower and Middle Valley of the Senegal river basin (SRB) demonstrate the existence of at least two strains of S. haematobium. The role of Bulinus truncatus in the transmission of S. haematobium in the Lower and Middle Valleys of the SRB is reviewed. Both S. haematobium and S. mansoni are transmitted in the same foci in some areas of the SRB.

Studies on the biology of schistosomiasis with emphasis on the Senegal river basin

The construction of the Diama dam on the Senegal river, the Manantali dam on the Bafing river, Mali and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni in Northern Senegal, associated with high intensity of infections, due to intense transmission, and the creation of new foci of S. haematobium. Data on the vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard Toll, Senegal are presented with sympatric and allopatric (Cameroon) S. mansoni. Comparisons are made on infectivity, cercarial production, chronobiology of cercarial emergence and longevity of infected snails. Recent data on the intermediate host specificity of different isolates of S. haematobium from the Lower and Middle Valley of the Senegal river basin (SRB) demonstrate the existence of at least two strains of S. haematobium. The role of Bulinus truncatus in the transmission of S. haematobium in the Lower and Middle Valleys of the SRB is reviewed. Both S. haematobium and S. mansoni are transmitted in the same foci in some areas of the SRB