Bio: Vr Southgate is an academic researcher from Natural History Museum. The author has contributed to research in topics: Schistosoma haematobium & Schistosoma intercalatum. The author has an hindex of 26, co-authored 66 publications receiving 1929 citations.
Papers published on a yearly basis
TL;DR: The principal findings are that Ornithobilharzia and AustrobilHarzia form a sister group to the Schistosoma; mammalian schistosomes appear paraphyletic and 2 TrichobilharZia species, T. ocellata and T. szidati, seem to be synonymous.
Abstract: Schistosomes are digenean flukes, parasitic of birds, mammals and crocodiles. The family Schistosomatidae contains species of considerable medical and veterinary importance, which cause the disease schistosomiasis. Previous studies, both morphological and molecular, which have provided a good deal of information on the phylogenetics of this group, have been limited in the number of species investigated or the type or extent of molecular data used. This paper presents the most comprehensive phylogeny to date, based on the sequences of 3 genes, complete ribosomal small subunit rRNA and large ribosomal subunit rRNA, and mitochondrial cytochrome oxidase 1, sequenced from 30 taxa including at least 1 representative from 10 of the 13 known genera of the Schistosomatidae and 17 of the 20 recognized Schistosoma species. The phylogeny is examined using morphological characters, intermediate and definitive host associations and biogeography. Theories as to the origins and spread of Schistosoma are also explored. The principal findings are that Ornithobilharzia and Austrobilharzia form a sister group to the Schistosoma; mammalian schistosomes appear paraphyletic and 2 Trichobilharzia species, T. ocellata and T. szidati, seem to be synonymous. The position of Orientobilharzia within the Schistosoma is confirmed, as is an Asian origin for the Schistosoma, followed by subsequent dispersal through India and Africa.
01 Jan 1987
TL;DR: Assessment of the extent of polyparasitism and the extent to which infections were focused in particular subsets of the study group found mean abundance of infection varied significantly between age classes, among schools and between the sexes, with females showing heavier mean EPGs for A. trichiura and males higher mean eggs/10 ml urine for S. haematobium infections.
Abstract: Prevalence and abundance of Schistosoma haematobium and soil-transmitted helminths (STH) were assessed among a total of 1600 pupils (urine, n = 1190; faecal samples, n = 1454) attending five schools in Loum, Littoral Province, Cameroon, with the specific aim of assessing the extent of polyparasitism and the extent to which infections were focused in particular subsets of the study group. Prevalence of S. haematobium was 62.8% with an abundance (arithmetic mean of egg counts) of 54 eggs/10 ml urine. For the STH these were 47.7% and 619 eggs per gram of faeces (EPG) for Trichuris trichiura, 65.5% and 3636 EPG for Ascaris lumbricoides, and 1.4% and <0.1 EPG for hookworms. Most children (90.3%) were infected with at least one of these four species, the largest proportion (34.3%) carrying two species; 27.4% carried three and 1.1% carried concurrently all four species of parasites. The average number of species harboured increased with age, as did the prevalences of S. haematobium and T. trichiura but not that of A. lumbricoides. All STH showed marked differences in prevalence between the five schools but only T. trichiura varied significantly between sexes. Mean abundance of infection varied significantly between age classes, among schools and between the sexes, with females showing heavier mean EPGs for A. lumbricoides and T. trichiura and males higher mean eggs/10 ml urine for S. haematobium infections. A highly significant association was detected between A. lumbricoides and T. trichiura, that was not context-dependent. This was confirmed in quantitative analyses after controlling for differences in abundance between schools, sexes and age classes. A weaker context-dependent association (prevalence data) was detected between S. haematobium and A. lumbricoides (sex- and age-dependent) but quantitative associations between these two species, as well as between S. haematobium and T. trichiura, were not convincing.
TL;DR: In this article, the authors conducted a study to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes.
Abstract: Extensive water development has taken place in the north of Senegal over the last decade, resulting in a large increase in the amount of fresh water for irrigation. The objectives of the present study were to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes. The schistosomiasis survey started in January 1994 and was completed in March 1995. Compared to studies before the construction of the Diama dam, there was a significant increase in both the prevalence and intensity of urinary and intestinal schistosomiasis in the human population in parts of the SRB. From the 9014 people who were registered from 180 villages and 4 towns (10 districts), 7750 were examined. S. mansoni was found in the lower valley (lower delta-Senegal river, lower delta-Lampsar river, upper delta, and diere ) but not in the middle valley. The mean prevalence ranged from 4.4% in the lower delta-Senegal River to 71.8% in the zone of Lac de Guiers, where prevalence and intensity of infection were higher on the eastern side of the lake (81.3% with a mean number of 2088 eggs/g of faeces) compared with the western side (50.3% with a mean 1111 eggs/g). S. haematobium was recorded throughout the area of study, ranging from a mean prevalence of 0.37% in diere (lower valley) to 41.5% in the lower valley (Lampsar river), where the mean egg count was 313/10 mL of urine. Physical and chemical changes to the environment have favoured the spread and increase in the populations of freshwater snails. The only snail involved in the transmission of S. mansoni was Biomphalaria pfeifferi . Five species of bulinid snails were present— Bulinus globosus, Bu. umbilicatus, Bu. senegalensis, Bu. forskalii and Bu. truncatus —but only the first 3 species were involved in the transmission of S. haematobium in the lower and middle valleys.
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: 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: It is concluded that the development and management of water resources is an important risk factor for schistosomiasis, and hence strategies to mitigate negative effects should become integral parts in the planning, implementation, and operation of future water projects.
Abstract: An estimated 779 million people are at risk of schistosomiasis, of whom 106 million (13.6%) live in irrigation schemes or in close proximity to large dam reservoirs. We identified 58 studies that examined the relation between water resources development projects and schistosomiasis, primarily in African settings. We present a systematic literature review and meta-analysis with the following objectives: (1) to update at-risk populations of schistosomiasis and number of people infected in endemic countries, and (2) to quantify the risk of water resources development and management on schistosomiasis. Using 35 datasets from 24 African studies, our meta-analysis showed pooled random risk ratios of 2.4 and 2.6 for urinary and intestinal schistosomiasis, respectively, among people living adjacent to dam reservoirs. The risk ratio estimate for studies evaluating the effect of irrigation on urinary schistosomiasis was in the range 0.02-7.3 (summary estimate 1.1) and that on intestinal schistosomiasis in the range 0.49-23.0 (summary estimate 4.7). Geographic stratification showed important spatial differences, idiosyncratic to the type of water resources development. We conclude that the development and management of water resources is an important risk factor for schistosomiasis, and hence strategies to mitigate negative effects should become integral parts in the planning, implementation, and operation of future water projects.
TL;DR: New insights into fundamental helminth biology are accumulating through newly completed genome projects and the nascent application of transgenesis and RNA interference technologies, which should one day translate into a new and robust pipeline of drugs, diagnostics, and vaccines for targeting parasitic worms that infect humans.
Abstract: Helminths are parasitic worms. They are the most common infectious agents of humans in developing countries and produce a global burden of disease that exceeds better-known conditions, including malaria and tuberculosis. As we discuss here, new insights into fundamental helminth biology are accumulating through newly completed genome projects and the nascent application of transgenesis and RNA interference technologies. At the same time, our understanding of the dynamics of the transmission of helminths and the mechanisms of the Th2-type immune responses that are induced by infection with these parasitic worms has increased markedly. Ultimately, these advances in molecular and medical helminth biology should one day translate into a new and robust pipeline of drugs, diagnostics, and vaccines for targeting parasitic worms that infect humans.
TL;DR: There is need for increased support for schistosomiasis control in the most severely affected countries, which are among the least developed whose health systems face difficulties to provide basic care at the primary health level.
Abstract: Schistosomiasis is being successfully controlled in many countries but remains a major public health problem, with an estimated 200 million people infected, mostly in Africa. Few countries in this region have undertaken successful and sustainable control programmes. The construction of water schemes to meet the power and agricultural requirements for development have lead to increasing transmission, especially of Schistosoma mansoni. Increasing population and movement have contributed to increased transmission and introduction of schistosomiasis to new areas. Most endemic countries are among the least developed whose health systems face difficulties to provide basic care at the primary health level. Constraints to control include, the lack of political commitment and infrastructure for public health interventions. Another constraint is that available anti-schistosomal drugs are expensive and the cost of individual treatment is a high proportion of the per capita drug budgets. There is need for increased support for schistosomiasis control in the most severely affected countries.
TL;DR: In this article, the authors used complete small subunit ribosomal RNA gene (ssrDNA) and partial (D1-D3) large subunit RIBG sequences to estimate the phylogeny of the Digenea via maximum parsimony and Bayesian inference.
Abstract: Complete small subunit ribosomal RNA gene (ssrDNA) and partial (D1‐ D3) large subunit ribosomal RNA gene (lsrDNA) sequences were used to estimate the phylogeny of the Digenea via maximum parsimony and Bayesian inference. Here we contribute 80 new ssrDNA and 124 new lsrDNA sequences. Fully complementary data sets of the two genes were assembled from newly generated and previously published sequences and comprised 163 digenean taxa representing 77 nominal families and seven aspidogastrean outgroup taxa representing three families. Analyses were conducted on the genes independently as well as combined and separate analyses including only the higher plagiorchiidan taxa were performed using a reduced-taxon alignment including additional characters that could not be otherwise unambiguously aligned. The combined data analyses yielded the most strongly supported results and differences between the two methods of analysis were primarily in their degree of resolution. The Bayesian analysis including all taxa and characters, and incorporating a model of nucleotide substitution (general-time-reversible with among-site rate heterogeneity), was considered the best estimate of the phylogeny and was used to evaluate their classification and evolution. In broad terms, the Digenea forms a dichotomy that is split between a lineage leading to the Brachylaimoidea, Diplostomoidea and Schistosomatoidea (collectively the Diplostomida nomen novum (nom. nov.)) and the remainder of the Digenea (the Plagiorchiida), in which the Bivesiculata nom. nov. and Transversotremata nom. nov. form the two most basal lineages, followed by the Hemiurata. The remainder of the Plagiorchiida forms a large number of independent lineages leading to the crown clade Xiphidiata nom. nov. that comprises the Allocreadioidea, Gorgoderoidea, Microphalloidea and Plagiorchioidea, which are united by the presence of a penetrating stylet in their cercariae. Although a majority of families and to a lesser degree, superfamilies are supported as currently defined, the traditional divisions of the Echinostomida, Plagiorchiida and Strigeida were found to comprise non-natural assemblages. Therefore, the membership of established higher taxa are emended, new taxa erected and a revised, phylogenetically based classification proposed and discussed in light of ontogeny, morphology and taxonomic history. q 2003 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.