Bio: J.R. Stothard is an academic researcher from Natural History Museum. The author has contributed to research in topics: Schistosoma haematobium & Bulinus. The author has an hindex of 14, co-authored 19 publications receiving 725 citations.
TL;DR: In this article, genetic variation between species representing the four species groups was assayed by Polymerase Chain Reaction (PCR) amplification of the ribosomal Internal Transcribed Spacer (ITS) region followed by Restriction Fragment Length Polymorphism (RFLP) analysis of this product with six restriction enzymes.
Abstract: Species within the genus Bulinus are responsible for transmission of schistosomes within the Schistosoma haematobium group. In order to provide a molecular insight into the species relationships within the genus, genetic variation between species representing the four species groups was assayed by Polymerase Chain Reaction (PCR) amplification of the ribosomal Internal Transcribed Spacer (ITS) region followed by Restriction Fragment Length Polymorphism (RFLP) analysis of this product with six restriction enzymes. This PCR-RFLP methodology detected considerable variation within the ITS region indicating that restriction profiles will be useful as genetic markers for identification purposes. The complete ITS1 spacer was sequenced for B. globosus, B. cernicus and B. truncatus. There were numerous nucleotide differences between taxa mainly insertions and deletions. Nucleotide divergence was calculated between species from the restriction profiles: the B. truncatus/tropicus complex and B. reticulatus group were most similar which were in turn more closely related to the B. africanus group than to the B. forskalii group. The nucleotide divergence between the species groups is substantial and questions the placement of these groups within the same genus.
TL;DR: Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.
Abstract: Within each of the four species groups of Bulinus there are species that act as intermediate hosts for one or more of the seven species of schistosomes in the Schistosoma haematobium group, which includes the important human pathogens S. haematobium and S. intercalatum. Bulinus species have an extensive distribution throughout much of Africa and some surrounding islands including Madagascar, parts of the Middle East and the Mediterranean region. Considerable variation in intermediate host specificity can be found and differences in compatibility between snail and parasite can be observed over small geographical areas. Molecular studies for detection of genetic variation and the discrimination of Bulinus species are reviewed and two novel assays, allele-specific amplification (ASA) and SNaPshot™, are introduced and shown to be of value for detecting nucleotide changes in characterized genes such as cytochrome oxidase 1. The value and complexity of compatibility studies is illustrated by case studies of S. haematobium transmission. In Senegal, where B. globosus, B. umbilicatus, B. truncatus and B. senegalensis may act as intermediate hosts, distinct differences have been observed in the infectivity of different isolates of S. haematobium. In Zanzibar, molecular characterization studies to discriminate between B. globosus and B. nasutus have been essential to elucidate the roles of snails in transmission. B. globosus is an intermediate host on Unguja and Pemba. Further studies are required to establish the intermediate hosts in the coastal areas of East Africa. Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.
TL;DR: Progress made in schistosomiasis control across sub-Saharan Africa since the turn of the new millennium is reviewed, shedding light on the latest findings stemming from clinical, epidemiological, molecular and social sciences research, inclusive of public health interventions with monitoring and evaluation activities.
Abstract: Several other journal supplements have documented progress made in the control of schistosomiasis in Egypt, China and Brazil, however, with more than 97% of the schistosome infections now estimated to occur in Africa, the relevance of this special issue in Parasitology cannot be overemphasized. In total, 18 articles are presented, inclusive of a lead-editorial from the WHO highlighting a seminal resolution at the 54th World Health Assembly in 2001 that advocated de-worming. Facilitated by a US$ 30 million grant from the Bill and Melinda Gates Foundation in 2002, the Schistosomiasis Control Initiative subsequently fostered implementation of large-scale schistosomiasis (and soil-transmitted helminthiasis) control programmes in six selected African countries. From 2005, CONTRAST, a European union-funded consortium, was formed to conduct multi-disciplinary research pertaining to optimisation of schistosomiasis control. Progress made in schistosomiasis control across sub-Saharan Africa since the turn of the new millennium is reviewed, shedding light on the latest findings stemming from clinical, epidemiological, molecular and social sciences research, inclusive of public health interventions with monitoring and evaluation activities. New opportunities for integrating the control of schistosomiasis and other so-called neglected tropical diseases are highlighted, but more importantly, several opportune questions that arise from it frame the remaining challenges ahead for an enduring solution.
TL;DR: Molecular data confirmed the existence of the snail, Lymnaea truncatula, at high altitude on the Kitulo Plateau of the Southern Highlands, Tanzania, along with morphometric and molecular data confirming the presence of F. hepatica in the corresponding area and analysis based on a 618 bp sequence of the 28S rRNA gene did not reveal the presenceof hybrid fasciolids in fluke samples.
Abstract: In East Africa, Fasciola gigantica is generally the causative agent of fasciolosis but there have been reports of F. hepatica in cattle from highland regions of Kenya, Ethiopia, Uganda and Zaire. The topography of the Southern Highlands of Tanzania provides an environment where the climatic conditions exist for the sustenance of lymnaeid species capable of supporting both Fasciola hepatica and F. gigantica. Theoretically this would allow interaction between fasciolid species and the possible creation of hybrids. In this report we present molecular data confirming the existence of the snail, Lymnaea truncatula, at high altitude on the Kitulo Plateau of the Southern Highlands, Tanzania, along with morphometric and molecular data confirming the presence of F. hepatica in the corresponding area. At lower altitudes, where climatic conditions were unfavourable for the existence of L. truncatula, the presence of its sister species L. natalensis was confirmed by molecular data along with its preferred fasciolid parasite, F. gigantica. Analysis based on a 618 bp sequence of the 28S rRNA gene did not reveal the presence of hybrid fasciolids in our fluke samples.
TL;DR: This RD-PCR proved highly sensitive, detecting a single larval stage and as little as 0.78 ng of genomic DNA from an adult schistosome, providing a cost-effective, rapid and robust molecular tool for high-throughput screening of S. haematobium and S. bovis populations.
Abstract: 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.
TL;DR: It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
Abstract: The relationship between the two estimates of genetic variation at the DNA level, namely the number of segregating sites and the average number of nucleotide differences estimated from pairwise comparison, is investigated. It is found that the correlation between these two estimates is large when the sample size is small, and decreases slowly as the sample size increases. Using the relationship obtained, a statistical method for testing the neutral mutation hypothesis is developed. This method needs only the data of DNA polymorphism, namely the genetic variation within population at the DNA level. A simple method of computer simulation, that was used in order to obtain the distribution of a new statistic developed, is also presented. Applying this statistical method to the five regions of DNA sequences in Drosophila melanogaster, it is found that large insertion/deletion (greater than 100 bp) is deleterious. It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
TL;DR: In this paper, the origins and geographical spread of F. gigantica and F. hepatica were investigated by means of complete sequences of ribosomal deoxyribonucleic acid (rDNA) internal transcribed spacer (ITS)−2 and ITS−1 and mitochondrial cox1 and nad1 from areas with only one fasciolid species.
Abstract: Fascioliasis, caused by liver fluke species of the genus Fasciola, has always been well recognized because of its high veterinary impact but it has been among the most neglected diseases for decades with regard to human infection. However, the increasing importance of human fascioliasis worldwide has re‐launched interest in fascioliasis. From the 1990s, many new concepts have been developed regarding human fascioliasis and these have furnished a new baseline for the human disease that is very different to a simple extrapolation from fascioliasis in livestock. Studies have shown that human fascioliasis presents marked heterogeneity, including different epidemiological situations and transmission patterns in different endemic areas. This heterogeneity, added to the present emergence/re‐emergence of the disease both in humans and animals in many regions, confirms a worrying global scenario. The huge negative impact of fascioliasis on human communities demands rapid action. When analyzing how better to define control measures for endemic areas differing at such a level, it would be useful to have genetic markers that could distinguish each type of transmission pattern and epidemiological situation. Accordingly, this chapter covers aspects of aetiology, geographical distribution, epidemiology, transmission and control in order to obtain a solid baseline for the interpretation of future results. The origins and geographical spread of F. hepatica and F. gigantica in both the ruminant pre‐domestication times and the livestock post‐domestication period are analyzed. Paleontological, archaeological and historical records, as well as genetic data on recent dispersal of livestock species, are taken into account to establish an evolutionary framework for the two fasciolids across all continents. Emphasis is given to the distributional overlap of both species and the roles of transportation, transhumance and trade in the different overlap situations. Areas with only one Fasciola spp. are distinguished from local and zonal overlaps in areas where both fasciolids co‐exist. Genetic techniques applied to liver flukes in recent years that are useful to elucidate the genetic characteristics of the two fasciolids are reviewed. The intra‐specific and inter‐specific variabilities of ‘pure’ F. hepatica and ‘pure’ F. gigantica were ascertained by means of complete sequences of ribosomal deoxyribonucleic acid (rDNA) internal transcribed spacer (ITS)‐2 and ITS‐1 and mitochondrial deoxyribonucleic acid (mtDNA) cox1 and nad1 from areas with only one fasciolid species. Fasciolid sequences of the same markers scattered in the literature are reviewed. The definitive haplotypes established appear to fit the proposed global evolutionary scenario. Problems posed by fasciolid cross‐breeding, introgression and hybridization in overlap areas are analyzed. Nuclear rDNA appears to correlate with adult fluke characteristics and fasciolid/lymnaeid specificity, whereas mtDNA does not. However, flukes sometimes appear so intermediate that they cannot be ascribed to either F. hepatica‐like or F. gigantica‐like forms and snail specificity may be opposite to the one deduced from the adult morphotype. The phenotypic characteristics of adults and eggs of ‘pure’ F. hepatica and F. gigantica, as well as of intermediate forms in overlap areas, are compared, with emphasis on the definitive host influence on egg size in humans. Knowledge is sufficient to support F. hepatica and F. gigantica as two valid species, which recently diverged by adaptation to different pecoran and lymnaeid hosts in areas with differing environmental characteristics. Their phenotypic differences and ancient pre‐domestication origins involve a broad geographical area that largely exceeds the typical, more local scenarios known for sub‐species units. Phenomena such as abnormal ploidy and aspermic parthenogenesis in hybrids suggest that their separate evolution in pre‐domestication times allowed them to achieve almost total genetic isolation. Recent sequencing results suggest that present assumptions on fasciolid‐lymnaeid specificity might be wrong. The crucial role of lymnaeids in fascioliasis transmission, epidemiology and control was the reason for launching a worldwide lymnaeid molecular characterization initiative. This initiative has already furnished useful results on several continents. A standardized methodology for fasciolids and lymnaeids is proposed herein in order that future work is undertaken on a comparable basis. A complete understanding of molecular epidemiology is expected to help greatly in designing global actions and local interventions for control of fascioliasis.
TL;DR: An agenda for the elimination of schistosomiasis would aim to identify the gaps in knowledge, and define the tools, strategies and guidelines that will help national control programmes move towards elimination, including an internationally accepted mechanism that allows verification/confirmation of elimination.
Abstract: It is time to raise global awareness to the possibility of schistosomiasis elimination and to support endemic countries in their quest to determine the most appropriate approaches to eliminate this persistent and debilitating disease. The main interventions for schistosomiasis control are reviewed, including preventive chemotherapy using praziquantel, snail control, sanitation, safe water supplies, and behaviour change strategies supported by information, education and communication (IEC) materials. Differences in the biology and transmission of the three main Schistosoma species (i.e. Schistosoma haematobium, S. mansoni and S. japonicum), which impact on control interventions, are considered. Sensitive diagnostic procedures to ensure adequate surveillance in areas attaining low endemicity are required. The importance of capacity building is highlighted. To achieve elimination, an intersectoral approach is necessary, with advocacy and action from local communities and the health community to foster cooperative ventures with engineers, the private sector, governments and non-governmental organizations specialized in water supply and sanitation. Examples of successful schistosomiasis control programmes are reviewed to highlight what has been learnt in terms of strategy for control and elimination. These include St. Lucia and other Caribbean islands, Brazil and Venezuela for S. mansoni; Saudi Arabia and Egypt for both S. mansoni and S. haematobium; Morocco, Tunisia, Algeria, Mauritius and the Islamic Republic of Iran for S. haematobium; Japan and the People's Republic of China for S. japonicum. Additional targets for elimination or even eradication could be the two minor human schistosome species S. guineenisis and S. intercalatum, which have a restricted distribution in West and Central Africa. The examples show that elimination of schistosomiasis is an achievable and desirable goal requiring full integration of preventive chemotherapy with the tools of transmission control. An agenda for the elimination of schistosomiasis would aim to identify the gaps in knowledge, and define the tools, strategies and guidelines that will help national control programmes move towards elimination, including an internationally accepted mechanism that allows verification/confirmation of elimination.
TL;DR: It is concluded that, for achieving integrated and sustainable control of neglected tropical diseases, a set of interventions must be tailored to a given endemic setting and fine-tuned over time in response to the changing nature and impact of control.
Abstract: In May 2001, the World Health Assembly (WHA) passed a resolution which urged member states to attain, by 2010, a minimum target of regularly administering anthelminthic drugs to at least 75% and up to 100% of all school-aged children at risk of morbidity. The refined global strategy for the prevention and control of schistosomiasis and soil-transmitted helminthiasis was issued in the following year and large-scale administration of anthelminthic drugs endorsed as the central feature. This strategy has subsequently been termed 'preventive chemotherapy'. Clearly, the 2001 WHA resolution led the way for concurrently controlling multiple neglected tropical diseases. In this paper, we recall the schistosomiasis situation in Africa in mid-2003. Adhering to strategic guidelines issued by the World Health Organization, we estimate the projected annual treatment needs with praziquantel among the school-aged population and critically discuss these estimates. The important role of geospatial tools for disease risk mapping, surveillance and predictions for resource allocation is emphasised. We clarify that schistosomiasis is only one of many neglected tropical diseases and that considerable uncertainties remain regarding global burden estimates. We examine new control initiatives targeting schistosomiasis and other tropical diseases that are often neglected. The prospect and challenges of integrated control are discussed and the need for combining biomedical, educational and engineering strategies and geospatial tools for sustainable disease control are highlighted. We conclude that, for achieving integrated and sustainable control of neglected tropical diseases, a set of interventions must be tailored to a given endemic setting and fine-tuned over time in response to the changing nature and impact of control. Consequently, besides the environment, the prevailing demographic, health and social systems contexts need to be considered.
TL;DR: Rigorous epidemiologic surveillance of soil-transmitted helminthiasis in the era of preventive chemotherapy is facilitated by multiple stool sampling bolstered by different diagnostic techniques.
Abstract: Background Soil-transmitted helminth infections are common throughout the tropics and subtropics and they disproportionately affect the poorest of the poor. In view of a growing global commitment to control soil-transmitted helminthiasis, there is a need to elucidate the effect of repeated stool sampling and the use of different diagnostic methods in areas targeted for preventive chemotherapy that are characterized by low-infection intensities. In this study, we focused on schoolchildren on Unguja Island, Zanzibar, an area where anthelminthic drugs have been repeatedly administered over the past decade.