Biomedical subjects

V R Southgate

Publications and source records attributed to V R Southgate.

At least 37 records · Page 2Linked to original sources

PubMed2002

Schistosoma ovuncatum n. sp. (Digenea: Schistosomatidae) from northwest Thailand and the historical biogeography of Southeast Asian Schistosoma Weinland, 1858.

Schistosoma sinensium Bao, 1958 was first isolated from an unidentified snail in Sichuan Province, PR China. This species was apparently rediscovered in Chiang Mai Province, northwest Thailand (Baidikul et al., 1984); the definitive host was the rat Rattus rattus and the intermediate host was the snail Tricula bollingi. In this paper S. sinensium is rediscovered in Sichuan Province and compared with worms recovered from experimentally infected mice, which had been exposed to cercariae shed by T. bollingi from Chiang Mai. Evidence is presented suggesting that the schistosome collected by Baidikul was not S. sinensium and that a new species is involved. The new species, named Schistosoma ovuncatum (etymology: ovum (egg) + uncatus (hooked)), is described and compared with related taxa. All previous papers on the Thai schistosome have used worms recovered from field-collected rodents only; this is the first account in which the life-cycle has been completed in the laboratory, using cercariae shed by T. bollingi, and the resulting worms described. S. ovuncatum differs from S. sinensium in terms of size and shape of body and egg, number of testes, size of ovary, length of vitellarium, intermediate host and biogeographical distribution. The relationships of the two taxa and their position with respect to the Schistosoma indicum- and S. japonicum-groups are discussed. The implications of the findings for the evolution of human schistosomiasis in the region are also commented upon.

Animals↗

PubMed2002

Implication of Bulinus truncatus in the transmission of urinary schistosomiasis in Senegal, West Africa.

Studies on the compatibility between Bulinus truncatus and Schistosoma haematobium from various areas in the Senegal River basin (SRB) were carried out, to investigate the role of B. truncatus in the epidemiology of urinary schistosomiasis in Senegal. The results show that B. truncatus from the Lower Valley is not compatible with S. haematobium from the Middle Valley. Interestingly, the study reveals that B. truncatus from the Upper Valley is compatible with S. haematobium from the same area, and that S. haematobium from the Middle Valley is compatible with B. truncatus from the Lower Valley. Bulinus truncatus naturally infected with S. haematobium have been collected from the Upper Valley of the SRB. These results indicate that B. truncatus is involved in the urinary schistosomiasis in Senegal.

Animals↗

PubMed2001

Molecular arguments for splitting of Schistosoma intercalatum, into two distinct species.

The taxonomic status of the two known strains of Schistosoma intercalatum, the Lower Guinea strain (originating from Edea, Cameroon) and the Zaire strain (originating from Kinshasa, Democratic Republic of Congo, formerly Zaire) was examined using random amplified polymorphic DNA (RAPD) markers. Two additional species within the S. haematobium group, S. haematobium and S. mattheei, were included in the study. DNA was extracted from four male and four female worms of each species and strain under investigation. In all, 13 primers gave reproducible and informative marker patterns; the monomorphic bands in all the males and females of each sample were scored, and 138 bands were included in the final analysis. Overall, 14 RAPD fragments were shared by all the schistosomes studied, and 19 RAPD fragments were considered to be sex markers. Only 22% (20/91) of the RAPD fragments were shared between S. intercalatum Zaire and S. intercalatum Cameroon. The mean values recorded for the Nei and Li's genetic distances between S. haematobium and S. mattheei and between S. intercalatum Zaire and S. intercalatum Cameroon were 0.546 and 0.596, respectively. A principal component analysis and one-way analysis of variance (ANOVA/MANOVA) showed a significant separation between S. intercalatum Zaire and S. intercalatum Cameroon. The data support the hypothesis that S. intercalatum Zaire and S. intercalatum Cameroon are distinct species. Additional molecular-biology studies are in progress that involve the use of nuclear and mitochondrial markers to confirm the extent of the genetic divergence prior to the establishment of final decision on the taxonomic status of the two strains of S. intercalatum.

Animals↗

PubMed2001

Lack of prezygotic isolation by assortative mating between the two cryptic species of the polytypic Schistosoma intercalatum taxon.

Ten mice were individually exposed to 30 male and 30 female cercariae of Schistosoma intercalatum from Cameroon and to 30 male and 30 female cercariae of S. intercalatum from Zaire. Ten weeks later, the nine surviving mice were killed, and a total of 263 adult schistosomes (228 pairs, 7 unpaired males, 28 unpaired females) were perfused. All worms were identified utilising the random amplified polymorphic DNA technique using primer OPG06 which enables the differentiation of the Cameroon and Zaire genotypes. The data demonstrate that there were no significant differences between the number of homospecific pairs observed compared with the expected number under the null hypothesis. Matings occurred in a random manner indicating that mate choice did not exist for the two genotypes of S. intercalatum. Hence there is no prezygotic isolation mechanism which would prevent the interaction of the two genotypes if they were sympatric. However, as they are allopatric, the possibility of the production of unfit hybrids does not arise. Consequently, the reinforcement of a prezygotic isolating mechanism does not play a significant role in the speciation process.

Animals↗

PubMed2001

In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel.

The resistance status of five praziquantel-susceptible and five praziquantel-resistant isolates was confirmed by chemotherapy in CD(1) mice with 3 x 200mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The five resistant isolates were less responsive to praziquantel than the five susceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on the in vitro responses of different stages of 10 isolates to praziquantel. There were different in vitro responses to praziquantel at the egg, miracidial, cercarial and adult stages of Schistosoma mansoni between praziquantel-resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of freshly hatched miracidia to 10(-6)M praziquantel for 1 min and observing the percent change in shape. Using this test it should be possible to determine whether failed therapy in patients infected with S. mansoni is due to the presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 x 10(-7)M praziquantel and observing the percent of tail shedding over 80 min it should be possible to monitor for the presence of praziquantel-resistant worms in snails collected in the field.

Animals↗

PubMed2001

Interactions between intermediate snail hosts of the genus Bulinus and schistosomes of the Schistosoma haematobium group.

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.

Africa↗

PubMed2001

Recent studies on Schistosoma intercalatum: taxonomic status, puzzling distribution and transmission foci revisited.

Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li's similarity index allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studies suggest that interspecific sexual interactions between human schistosomes could have a role in limiting the distribution of S. intercalatum: the competitive sexual processes acting among human schistosomes show that S. haematobium and S. mansoni are always competitively dominant over S. intercalatum. These epidemiological observations lead the authors to distinguish three kinds of transmission foci for S. intercalatum.

Africa↗

PubMed2000

Changes of mate occur in Schistosoma mansoni.

Male and female schistosomes are generally assumed to form stable monogamous pairs for the whole span of their long existence in the mammalian host. Recent evidence from mixed infections has shown that Schistosoma mansoni males can displace S. intercalatum males from their homologous partners, but no information exists about the existence of similar phenomena within a single schistosome species. Here, we determine whether male S. mansoni can displace males of the same species from pre-formed pairs in vivo. The availability of clear-cut genetic markers of drug resistance in schistosomes was exploited to show that hycanthone sensitive S. mansoni males can displace homospecific hycanthone resistant males from pre-formed pairs and vice versa. The frequency of changes is dependent on the magnitude of the excess single males competing with paired worms. The possible mechanics and the biological significance of mate changing are discussed.

Animals↗

PubMed2000

Compatibility of Schistosoma mansoni Cameroon and Biomphalaria pfeifferi Senegal.

The vectorial capacity of Biomphalaria pfeifferi from Ndiangue, Senegal, was investigated with an allopatric isolate of Schistosoma mansoni from Nkolbisson, Cameroon. The snail infection rate after exposure to a single miracidium per snail (MD1) was 56. 3 %, and 91.6%, for snails exposed to 5 miracidia per snail (MD5). The minimum pre-patent period was 21 days. The mean total cercarial production for the MDI group was 18,511 cercariae per snail, and 9757 cercariae for the MD5 group. The maximum production of cercariae for 1 day was 4892 observed in a snail from the MDI group at day 43 post-infection. The mean longevity of snails was higher in group MD1 (88 days p.i.) than in group MD5 (65 days p.i.). The chronobiological emergence pattern revealed a circadian rhythm with one shedding peak at mid-day. Comparisons are made with the vectorial capacity of the sympatric combination of B. pfeifferi Senegal/S. mansoni Senegal.

Animals↗

PubMed2000

Observations on the compatibility between Bulinus spp. and Schistosoma haematobium in the Senegal River basin.

Snail-infection experiments were carried out with a number of different species and populations of Bulinus and isolates of Schistosoma haematobium. The parasites came from six localities in the Senegal River basin (SRB), in the Lower Valley (Mbodiene), Middle Valley (Podor, Diatar and Nguidjilone), and Upper Valley (Aroundou and Galladé). Isolates of S. haematobium from the Middle and Upper Valleys all showed some compatibility with laboratory-bred B. truncatus from Mali, but none of these isolates was compatible with laboratory-bred B. truncatus originating from Senegal. Schistosoma haematobium from Diatar (Middle Valley) was compatible with B. senegalensis, whereas S. haematobium from Mbodiene (Lower Valley), which is naturally transmitted by B. globosus, was incompatible with B. senegalensis and B. truncatus. These data demonstrate that different isolates of S. haematobium from different regions of the SRB exhibit distinct intermediate-host specificities, which in turn will have an effect on the epidemiology of the disease, including the periods of transmission. It is apparent that, in addition to B. senegalensis and B. globosus, B. truncatus, the most widespread bulinid snail in the SRB, may be playing a role in the epidemiology of urinary schistosomiasis. This conclusion has obvious implications for the future spread of urinary schistosomiasis in the SRB. Chemical and physical measurements from assorted habitats along the SRB, including pH, temperature, salinity, conductivity, and resistivity, are also reported.

Animals↗

PubMed2000

The effects of irrigated agriculture on the transmission of urinary schistosomiasis in the Middle and Upper Valleys of the Senegal River basin.

The importance of the increase in irrigated land on the perimeters of the Middle and Upper Valleys of the Senegal River basin, on the prevalence and intensity of urinary schistosomiasis, was investigated. Surveys were conducted, in May-June 1997, to determine the prevalence and intensity of Schistosoma haematobium infection among 1445 children aged 7-14 years: 1011 in 10 villages near Matam, and 434 in four villages near Bakel. Macrohaematuria was present in seven of the study villages (four near Matan and three near Bakel), whereas microhaematuria was present in all the villages, with prevalences of 10%-73%. A second survey, conducted, in June 1999, on 755 children from nine of the study villages near Matam, demonstrated significant increases in the prevalences of both micro- and macro-haematuria in three of the villages, all of which were adjacent to the Senegal River and practising irrigated agriculture. None of the other study villages re-surveyed was irrigating any of its agricultural land. A longitudinal survey was also carried out, between May 1997 and November 1998, on about 10% of the population (2272 subjects) of Nguidjilone, north of Matam; selective treatment with praziquantel (40 mg/kg) was given in May 1997, and mass treatment in May 1998. The data analysed were those relating to the 125 individuals who provided samples at each survey. Very severe infections (> 1000 eggs/10 ml urine) were seen in five subjects in May 1997. One year later (i.e. 1 year after the selective treatment), the prevalence of urinary schistosomiasis had increased in every age-group. Although prevalence had decreased slightly by November 1998 (6 months after the mass treatment), the intensity of the infections seen had increased in every age-group. At the end of the dry season (May-June 1997), Bulinus truncalus infected with schistosome cercariae were recovered from the Senegal River. However, immediately after the next rainy season (November 1997), no snails were found at any collection site on the river.

Adolescent↗

PubMed1999

Compatibility of Schistosoma mansoni and Biomphalaria pfeifferi in northern Senegal.

The construction of the Diama dam on the Senegal River and the ensuing ecological changes have led to a massive outbreak of Schistosoma mansoni infection in Northern Senegal, associated with very high intensity of infections, due to extremely intense transmission. The vectorial capacity of Biomphalaria pfeifferi from Ndombo, near Richard-Toll was investigated in order to assess the role of the snail-parasite relationship in this particular epidemiological situation. The results revealed an unusually high compatibility between the Senegalese S. mansoni strain and its local snail intermediate host, B. pfeifferi. The snail infection rate after exposure to a single miracidium per snail was 87%. The cercarial production of infected snails was very high, with a mean total production of 50,456 cercariae per snail. No significant difference was found in the total cercarial output between snails exposed to 1 miracidium and those exposed to 5 miracidia. The increase in the rate of cercarial output was significantly greater in snails exposed to 5 miracidia, but there was a higher mortality in this group. The chronobiological cercarial production pattern showed a peak around mid-day. The implications of these findings on the epidemiology of schistosomiasis in Northern Senegal are discussed.

Animals↗

PubMed1999

Mating interactions between Schistosoma haematobium and S. mansoni.

Schistosoma haematobium and S. mansoni are two medically important schistosomes, commonly occurring sympatrically in Africa and so potentially able to infect the same human host. Experiments were designed to study the mating behaviour of these two species in mixed infections in hamsters. Analysis of the data obtained showed that both heterospecific and homospecific pairs readily form. No significant difference was seen between the two species in their ability in forming pairs, however, S. mansoni showed a greater homospecific mate preference. Analysis of the data using the Mantel-Haenszel test suggests that mating competition does occur between S. haematobium and S. mansoni, the former being the more dominant species. Both species appeared to be able to change mate, with S. haematobium showing a greater ability in taking S. mansoni females away from S. mansoni males when introduced into a pre-established S. mansoni infection highlighting the competitiveness of S. haematobium. The significance of the results is discussed in relation to the epidemiological consequences occurring in Senegal, and other areas where both species are sympatric.

Animals↗

PubMed1998

Recent studies on the reproductive biology of the schistosomes and their relevance to speciation in the Digenea.

The members of the family Schistosomatidae, dioecious Digenea, are discussed with regard to their distribution, intermediate and definitive host-parasite relationships. The biological species concept is considered together with the difficulties of its application to Schistosoma spp. and the Digenea. The correlation between pairing of adult schistosomes, physical and sexual development and the maintenance of reproductive potential is emphasised. Development of the female reproductive system does not depend upon species-specific pairing. In some combinations, e.g., Schistosoma haematobium/Schistosoma intercalatum and Schistosoma bovis/Schistosoma curassoni, a specific mate choice system apparently does not exist, whereas it does in other combinations, e.g., Schistosoma mansoni/Schistosoma intercalatum. In mixed infections change of mate may occur and when the opportunity arises heterospecific pairs of worms will change partners to conspecific pairs. Interspecific pairing in adult schistosomes will lead to either hybridisation or parthenogenesis. Yet the majority of schistosomes that inhabit the same definitive host maintain their genetic identity: specific mate recognition, site selection within the host and heterologous immunity have been suggested as isolating mechanisms. Experimental intraspecific crosses have enabled evaluation of the degree to which some populations separated and became reproductively isolated through pre-mating isolating mechanisms, indicative of incipient speciation, e.g., the Lower Guinea and Zaire strains of S. intercalatum. The occurrence and significance of parthenogenesis in schistosomes and other species of Digenea are discussed. The consequences of interspecific mating interactions in schistosomes with regard to parasite epidemiology, interspecific competition and genetic heterogeneity are debated. Geographical isolation and host specificity represent important pre-zygotic isolating mechanisms. It is suggested that site selection within the host and heterologous immunity may both reduce interspecific genetic interchange when digenean parasites utilise the same definitive host.

Animals↗

PubMed1997

Schistosomiasis in the Senegal River Basin: before and after the construction of the dams at Diama, Senegal and Manantali, Mali and future prospects.

Ecological changes in the Senegal River Basin (SRB) resulting from the construction of a barrage at Diama, Senegal on the Senegal River to prevent the intrusion of sea water into the river, and a dam at Manantali, Mali on the Bafing River to control the flow of water and to generate electricity, have been responsible for changes in the epidemiology of human schistosomiasis. The introduction of Schistosoma mansoni into the Lower and Middle Valleys of the SRB and subsequent spread of the parasite in the human population is recorded with regard to prevalence and intensity. New foci of S. haematobium are described. The reduction in salinity and change from an acidic to an alkaline environment in the water are beneficial to both the fecundity and growth of freshwater snails and transmission of the parasite. The creation of new irrigation canals and expansion of the rice fields have provided new habitats for intermediate hosts to colonize. The evidence for praziquantel resistance/tolerance by populations of S. mansoni and the possibilities of the development, production and testing of a vaccine against human schistosomiasis are discussed. Future studies will monitor the spread of human urinary and mesenteric schistosomiasis in the SRB, will evaluate further the presence of praziquantel resistance/tolerance in S. mansoni, will examine the heavily infected human population for pathological symptoms and determine the most appropriate methods to control this severe outbreak of human schistosomiasis.

Animals↗

PubMed1997

Comparison of human and murine isolates of Schistosoma mansoni from Richard-Toll, Senegal, by isoelectric focusing.

Studies on human and murine isolates of Schistosoma mansoni, from Richard-Toll, Senegal, were carried out by isoelectric focusing in polyacrylamide gels. Seven enzyme systems; lactate dehydrogenase (LDH), malate dehydrogenase (MDH), glucose-6-phosphate dehydrogenase (G6PD), acid phosphatase (AcP), hexokinase (HK), glucose phosphate isomerase (GPI), and phosphoglucomutase (PGM), were used to compare the two isolates. All systems tested, apart from LDH, were found to be polymorphic for both isolates. Interestingly, one phenotype is more frequent than the remainder. The results show that there is no significant genetic variation between the S. mansoni isolates from man and the rodents, Arvicanthis niloticus and Mastomys huberti.

Acid Phosphatase↗

PubMed1997

Infectivity of a Cambodian isolate of Schistosoma mekongi to Neotricula aperta from northeast Thailand.

All three strains of Neotricula aperta (Gastropoda: Pomatiopsidae) sampled from populations in northeast Thailand were found to be compatible with a Schistosoma mekongi isolate from Kratie District, eastern Cambodia. The infection rates were: 3.0%, alpha-strain; 6.0%, beta-strain, and 20.5%, gamma-strain. The greater infectivity to the gamma-strain, over both the alpha- and beta-strains, was statistically significant. Comparisons of infectivity patterns for the Kratie isolate, with those described in earlier studies using S. mekongi isolates from southern Laos, revealed differences among the strains. The gamma-strain of N. aperta is responsible for endemic transmission of human schistosomiasis in southern Laos and at Kratie. Consequently, the findings of this study are of use in the prediction of changes in the distribution of Mekong schistosomiasis, particularly its introduction to northeast Thailand from the neighbouring countries, Cambodia and Laos.

Animals↗

PubMed1997

Observations on compatibility between Bulinus truncatus and Schistosoma haematobium in the Senegal River Basin.

In experiments to determine the compatibility between isolates of Schistosoma haematobium and Bulinus truncatus from Mali and Senegal, the parasite isolates were shown to differ in their intermediate host specificity. Bulinus truncatus from the Lower and Middle Valleys (Senegal) and the Upper Valley (Mali) of the Senegal River Basin (SRB) were all susceptible to S. haematobium isolated from the urines of children living in Tenegue, Office du Niger, Mali. However, none of the B. truncatus tested was susceptible to a parasite isolated from children living in Mbodiene, a village in the Lower Valley of the SRB, where natural transmission is normally associated with B. globosus. As B. truncatus is widely distributed in the SRB, the possible appearance of a Bulinus-truncatus-borne parasite in the Middle and Lower Valleys should be carefully monitored.

Animals↗