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Choi YJ, Fischer K, Méité A, Koudou BG, Fischer PU, Mitreva M. Distinguishing recrudescence from reinfection in lymphatic filariasis. EBioMedicine 2024; 105:105188. [PMID: 38848649 PMCID: PMC11200287 DOI: 10.1016/j.ebiom.2024.105188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Revised: 05/21/2024] [Accepted: 05/23/2024] [Indexed: 06/09/2024] Open
Abstract
BACKGROUND The Global Program to Eliminate Lymphatic Filariasis (GPELF) is the largest public health program based on mass drug administration (MDA). Despite decades of MDA, ongoing transmission in some countries remains a challenge. To optimise interventions, it is critical to differentiate between recrudescence and new infections. Since adult filariae are inaccessible in humans, deriving a method that relies on the offspring microfilariae (mf) is necessary. METHODS We developed a genome amplification and kinship analysis-based approach using Brugia malayi samples from gerbils, and applied it to analyse Wuchereria bancrofti mf from humans in Côte d'Ivoire. We examined the pre-treatment genetic diversity in 269 mf collected from 18 participants, and further analysed 1-year post-treatment samples of 74 mf from 4 participants. Hemizygosity of the male X-chromosome allowed for direct inference of haplotypes, facilitating robust maternal parentage inference. To enrich parasite DNA from samples contaminated with host DNA, a whole-exome capture panel was created for W. bancrofti. FINDINGS By reconstructing and temporally tracking sibling relationships across pre- and post-treatment samples, we differentiated between new and established maternal families, suggesting reinfection in one participant and recrudescence in three participants. The estimated number of reproductively active adult females ranged between 3 and 11 in the studied participants. Population structure analysis revealed genetically distinct parasites in Côte d'Ivoire compared to samples from other countries. Exome capture identified protein-coding variants with ∼95% genotype concordance rate. INTERPRETATION We have generated resources to facilitate the development of molecular genetic tools that can estimate adult worm burdens and monitor parasite populations, thus providing essential information for the successful implementation of GPELF. FUNDING This work was financially supported by the Bill and Melinda Gates Foundation (https://www.gatesfoundation.org) under grant OPP1201530 (Co-PIs PUF & Gary J. Weil). B. malayi parasite material was generated with support of the Foundation for Barnes Jewish Hospital (PUF). In addition, the development of computational methods was supported by the National Institutes of Health under grants AI144161 (MM) and AI146353 (MM). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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Affiliation(s)
- Young-Jun Choi
- Infectious Diseases Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Kerstin Fischer
- Infectious Diseases Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Aboulaye Méité
- Programme National de la Lutte Contre la Schistosomiase, Les Geohelminthiases et la Filariose Lymphatique, Abidjan, Côte d'Ivoire
| | - Benjamin G Koudou
- Centre Suisse de Recherche Scientifique en Côte d'Ivoire, Abidjan, Côte d'Ivoire; Université Nangui Abrogoua, Abidjan, Côte d'Ivoire
| | - Peter U Fischer
- Infectious Diseases Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Makedonka Mitreva
- Infectious Diseases Division, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA; Department of Genetics, Washington University School of Medicine, St. Louis, MO, USA; McDonnell Genome Institute, Washington University in St. Louis, St. Louis, MO, USA.
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Choi YJ, Fischer K, Méité A, Koudou BG, Fischer PU, Mitreva M. Distinguishing recrudescence from reinfection in lymphatic filariasis: a genomics-based approach for monitoring worm burden. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.11.05.23297155. [PMID: 37986785 PMCID: PMC10659506 DOI: 10.1101/2023.11.05.23297155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Background The Global Program to Eliminate Lymphatic Filariasis is the largest public health program based on mass drug administration (MDA). Despite decades of MDA, ongoing transmission in some countries remains a challenge. To optimize interventions, it is essential to differentiate between recrudescence (poor drug response and persistent infection) and new infections (ongoing transmission). Since adult filariae are inaccessible in humans, an approach that relies on genotyping the offspring microfilariae (mf) is required. Methods We utilized Brugia malayi adults and mf obtained from gerbils with a known pedigree to develop and validate our whole-genome amplification and kinship analysis approach. We then sequenced the genomes of Wuchereria bancrofti mf from infected humans from Côte d'Ivoire (CDI), characterized the population genetic diversity, and made inferences about the adult breeders. We developed a whole-exome capture panel for W. bancrofti to enrich parasite nuclear DNA from lower-quality samples contaminated with host DNA. Results We established a robust analysis pipeline using B. malayi adult and mf. We estimated the pre-treatment genetic diversity in W. bancrofti from 269 mf collected from 18 individuals, and further analyzed 1-year post-treatment samples of 74 mf from 4 individuals. By reconstructing and temporally tracking sibling relationships across pre- and post-treatment samples, we differentiated between new and established maternal families, suggesting reinfection in one subject and recrudescence in three subjects. Estimated reproductively active adult females ranged between 3 and 9 in the studied subjects. Hemizygosity of the male X-chromosome allowed for direct inference of haplotypes, facilitating robust maternal parentage inference, even when the genetic diversity was low. Population structure analysis revealed genetically distinct parasites among our CDI samples. Sequence composition and variant analysis of whole-exome libraries showed that the hybridization capture approach can effectively enrich parasite nuclear DNA and identify protein-coding variants with ∼95% genotype concordance rate. Conclusions We have generated resources to facilitate development of field-deployable genotyping tools that can estimate worm burdens and monitor parasite populations. These tools are essential for the success of lymphatic filariasis MDA programs. With further expansion of the databases to include geographically diverse samples, we will be able to spatially track parasite movement associated with host/vector migration.
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Thorn CS, Maness RW, Hulke JM, Delmore KE, Criscione CD. Population genomics of helminth parasites. J Helminthol 2023; 97:e29. [PMID: 36927601 DOI: 10.1017/s0022149x23000123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
Next generation sequencing technologies have facilitated a shift from a few targeted loci in population genetic studies to whole genome approaches. Here, we review the types of questions and inferences regarding the population biology and evolution of parasitic helminths being addressed within the field of population genomics. Topics include parabiome, hybridization, population structure, loci under selection and linkage mapping. We highlight various advances, and note the current trends in the field, particularly a focus on human-related parasites despite the inherent biodiversity of helminth species. We conclude by advocating for a broader application of population genomics to reflect the taxonomic and life history breadth displayed by helminth parasites. As such, our basic knowledge about helminth population biology and evolution would be enhanced while the diversity of helminths in itself would facilitate population genomic comparative studies to address broader ecological and evolutionary concepts.
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Affiliation(s)
- C S Thorn
- Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX, 77843, USA
| | - R W Maness
- Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX, 77843, USA
| | - J M Hulke
- Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX, 77843, USA
| | - K E Delmore
- Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX, 77843, USA
| | - C D Criscione
- Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX, 77843, USA
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4
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Revisiting density-dependent fecundity in schistosomes using sibship reconstruction. PLoS Negl Trop Dis 2021; 15:e0009396. [PMID: 33983965 PMCID: PMC8148369 DOI: 10.1371/journal.pntd.0009396] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Revised: 05/25/2021] [Accepted: 04/19/2021] [Indexed: 11/19/2022] Open
Abstract
The stability of parasite populations is regulated by density-dependent processes occurring at different stages of their life cycle. In dioecious helminth infections, density-dependent fecundity is one such regulatory process that describes the reduction in egg production by female worms in high worm burden within-host environments. In human schistosomiasis, the operation of density-dependent fecundity is equivocal and investigation is hampered by the inaccessibility of adult worms that are located intravascularly. Current understanding is almost exclusively limited to data collected from two human autopsy studies conducted over 40 years ago, with subsequent analyses having reached conflicting conclusions. Whether egg production is regulated in a density-dependent manner is key to predicting the effectiveness of interventions targeting the elimination of schistosomiasis and to the interpretation of parasitological data collected during monitoring and evaluation activities. Here, we revisit density-dependent fecundity in the two most globally important human Schistosoma spp. using a statistical modelling approach that combines molecular inference on the number of parents/adult worms in individual human hosts with parasitological egg count data from mainland Tanzania and Zanzibar. We find a non-proportional relationship between S. haematobium egg counts and inferred numbers of female worms, providing the first clear evidence of density-dependent fecundity in this schistosome species. We do not find robust evidence for density-dependent fecundity in S. mansoni because of high sensitivity to some modelling assumptions and the lower statistical power of the available data. We discuss the strengths and limitations of our model-based analytical approach and its potential for improving our understanding of density dependence in schistosomiasis and other human helminthiases earmarked for elimination. Schistosomiasis is a devastating disease of poverty currently estimated to infect over 220 million people. It is caused by parasitic worms (blood flukes) that live for, on average, 5–7 years inside the blood vessels of infected hosts and produce hundreds of eggs daily. Whether egg production is regulated in a density-dependent manner, and if so under what conditions, has been controversial for schistosomiasis, and investigation is hampered due to the inaccessible location of adult worms. Resolving this fundamental question is important because density dependencies determine the resilience of helminthiases to interventions. Here, we have revisited this longstanding and unresolved question of density-dependent fecundity in human schistosomes using a novel statistical modelling approach that combines information from molecular and parasitological data. We report the first clear evidence of density-dependent fecundity in S. haematobium, the causative agent of millions of cases of urogenital schistosomiasis. Our findings are of critical importance both to mathematical modellers predicting the impact of interventions and to public health policy makers striving to meet the 2030 elimination targets for schistosomiasis. This study also serves to illustrate a new biostatistical approach that could be applied to investigate density dependencies in other helminthiases where adult parasites are inaccessible.
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Rey O, Webster BL, Huyse T, Rollinson D, Van den Broeck F, Kincaid-Smith J, Onyekwere A, Boissier J. Population genetics of African Schistosoma species. INFECTION GENETICS AND EVOLUTION 2021; 89:104727. [PMID: 33486128 DOI: 10.1016/j.meegid.2021.104727] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 01/09/2021] [Accepted: 01/13/2021] [Indexed: 02/06/2023]
Abstract
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.
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Affiliation(s)
- O Rey
- Univ. Montpellier, CNRS, IFREMER, UPVD, IHPE, F-66000 Perpignan, France
| | - B L Webster
- Wolfson Wellcome Biomedical Laboratories, Department of Life Sciences, Natural History Museum, London SW7 5BD, United Kingdom; London Centre for Neglected Tropical Disease Research, Imperial College London School of Public Health, London W2 1PG, United Kingdom
| | - T Huyse
- Department of Biology, Royal Museum for Central Africa, Leuvensesteenweg 13, B-3080 Tervuren, Belgium; Laboratory of Biodiversity and Evolutionary Genomics, Department of Biology, KU Leuven, Ch. Deberiotstraat 32, B-3000 Leuven, Belgium
| | - D Rollinson
- Wolfson Wellcome Biomedical Laboratories, Department of Life Sciences, Natural History Museum, London SW7 5BD, United Kingdom; London Centre for Neglected Tropical Disease Research, Imperial College London School of Public Health, London W2 1PG, United Kingdom
| | - F Van den Broeck
- Department of Microbiology, Immunology and Transplantation, Rega Institute for Medical Research, University of Leuven, Leuven, Belgium; Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - J Kincaid-Smith
- Centre for Emerging, Endemic and Exotic Diseases (CEEED), Department of Pathobiology and Population Sciences (PPS), Royal Veterinary College, University of London, Hawkshead Campus, Herts AL9 7TA, United Kingdom
| | - A Onyekwere
- Univ. Montpellier, CNRS, IFREMER, UPVD, IHPE, F-66000 Perpignan, France
| | - J Boissier
- Univ. Montpellier, CNRS, IFREMER, UPVD, IHPE, F-66000 Perpignan, France.
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Webster JP, Neves MI, Webster BL, Pennance T, Rabone M, Gouvras AN, Allan F, Walker M, Rollinson D. Parasite Population Genetic Contributions to the Schistosomiasis Consortium for Operational Research and Evaluation within Sub-Saharan Africa. Am J Trop Med Hyg 2020; 103:80-91. [PMID: 32400355 PMCID: PMC7351308 DOI: 10.4269/ajtmh.19-0827] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Analyses of the population genetic structure of schistosomes under the "Schistosomiasis Consortium for Operational Research and Evaluation" (SCORE) contrasting treatment pressure scenarios in Tanzania, Niger, and Zanzibar were performed to provide supplementary critical information with which to evaluate the impact of these large-scale control activities and guide how activities could be adjusted. We predicted that population genetic analyses would reveal information on a range of important parameters including, but not exclusive to, recruitment and transmission of genotypes, occurrence of hybridization events, differences in reproductive mode, and degrees of inbreeding, and hence, the evolutionary potential, and responses of parasite populations under contrasting treatment pressures. Key findings revealed that naturally high levels of gene flow and mixing of the parasite populations between neighboring sites were likely to dilute any effects imposed by the SCORE treatment arms. Furthermore, significant inherent differences in parasite fecundity were observed, independent of current treatment arm, but potentially of major impact in terms of maintaining high levels of ongoing transmission in persistent "biological hotspot" sites. Within Niger, naturally occurring Schistosoma haematobium/Schistosoma bovis viable hybrids were found to be abundant, often occurring in significantly higher proportions than that of single-species S. haematobium infections. By examining parasite population genetic structures across hosts, treatment regimens, and the spatial landscape, our results to date illustrate key transmission processes over and above that which could be achieved through standard parasitological monitoring of prevalence and intensity alone, as well as adding to our understanding of Schistosoma spp. life history strategies in general.
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Affiliation(s)
- Joanne P Webster
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom.,Department of Pathobiology and Population Sciences, Centre for Emerging, Endemic and Exotic Diseases (CEEED), Royal Veterinary College, University of London, Hawkshead Campus, Herts, United Kingdom
| | - Maria Inês Neves
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom.,Department of Pathobiology and Population Sciences, Centre for Emerging, Endemic and Exotic Diseases (CEEED), Royal Veterinary College, University of London, Hawkshead Campus, Herts, United Kingdom
| | - Bonnie L Webster
- Department of Life Sciences, Wolfson Wellcome Biomedical Laboratories, The Natural History Museum, London, United Kingdom.,London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom
| | - Tom Pennance
- School of Biosciences, Cardiff University, Cardiff, United Kingdom.,Department of Life Sciences, Wolfson Wellcome Biomedical Laboratories, The Natural History Museum, London, United Kingdom.,London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom
| | - Muriel Rabone
- Department of Life Sciences, Wolfson Wellcome Biomedical Laboratories, The Natural History Museum, London, United Kingdom.,London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom
| | - Anouk N Gouvras
- Department of Life Sciences, Wolfson Wellcome Biomedical Laboratories, The Natural History Museum, London, United Kingdom.,London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom
| | - Fiona Allan
- Department of Life Sciences, Wolfson Wellcome Biomedical Laboratories, The Natural History Museum, London, United Kingdom.,London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom
| | - Martin Walker
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom.,Department of Pathobiology and Population Sciences, Centre for Emerging, Endemic and Exotic Diseases (CEEED), Royal Veterinary College, University of London, Hawkshead Campus, Herts, United Kingdom
| | - David Rollinson
- Department of Life Sciences, Wolfson Wellcome Biomedical Laboratories, The Natural History Museum, London, United Kingdom.,London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College Faculty of Medicine, London, United Kingdom
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Platt RN, McDew-White M, Le Clec’h W, Chevalier FD, Allan F, Emery AM, Garba A, Hamidou AA, Ame SM, Webster JP, Rollinson D, Webster BL, Anderson TJC. Ancient Hybridization and Adaptive Introgression of an Invadolysin Gene in Schistosome Parasites. Mol Biol Evol 2019; 36:2127-2142. [PMID: 31251352 PMCID: PMC6759076 DOI: 10.1093/molbev/msz154] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Introgression among parasite species has the potential to transfer traits of biomedical importance across species boundaries. The parasitic blood fluke Schistosoma haematobium causes urogenital schistosomiasis in humans across sub-Saharan Africa. Hybridization with other schistosome species is assumed to occur commonly, because genetic crosses between S. haematobium and livestock schistosomes, including S. bovis, can be staged in the laboratory, and sequencing of mtDNA and rDNA amplified from microscopic miracidia larvae frequently reveals markers from different species. However, the frequency, direction, age, and genomic consequences of hybridization are unknown. We hatched miracidia from eggs and sequenced the exomes from 96 individual S. haematobium miracidia from infected patients from Niger and the Zanzibar archipelago. These data revealed no evidence for contemporary hybridization between S. bovis and S. haematobium in our samples. However, all Nigerien S. haematobium genomes sampled show hybrid ancestry, with 3.3-8.2% of their nuclear genomes derived from S. bovis, providing evidence of an ancient introgression event that occurred at least 108-613 generations ago. Some S. bovis-derived alleles have spread to high frequency or reached fixation and show strong signatures of directional selection; the strongest signal spans a single gene in the invadolysin gene family (Chr. 4). Our results suggest that S. bovis/S. haematobium hybridization occurs rarely but demonstrate profound consequences of ancient introgression from a livestock parasite into the genome of S. haematobium, the most prevalent schistosome species infecting humans.
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Affiliation(s)
- Roy N Platt
- Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX
| | - Marina McDew-White
- Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX
| | - Winka Le Clec’h
- Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX
| | - Frédéric D Chevalier
- Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX
| | - Fiona Allan
- Department of Life Sciences, The Natural History Museum, London, United Kingdom
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College London, St Mary’s Campus, London, United Kingdom
| | - Aidan M Emery
- Department of Life Sciences, The Natural History Museum, London, United Kingdom
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College London, St Mary’s Campus, London, United Kingdom
| | - Amadou Garba
- Réseau International Schistosomoses, Environnement, Aménagement et Lutte (RISEAL-Niger), Niamey, Niger
| | - Amina A Hamidou
- Réseau International Schistosomoses, Environnement, Aménagement et Lutte (RISEAL-Niger), Niamey, Niger
| | - Shaali M Ame
- Public Health Laboratory - Ivo de Carneri, Pemba, United Republic of Tanzania
| | - Joanne P Webster
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College London, St Mary’s Campus, London, United Kingdom
- Centre for Emerging, Endemic and Exotic Diseases, Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, London, United Kingdom
| | - David Rollinson
- Department of Life Sciences, The Natural History Museum, London, United Kingdom
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College London, St Mary’s Campus, London, United Kingdom
| | - Bonnie L Webster
- Department of Life Sciences, The Natural History Museum, London, United Kingdom
- London Centre for Neglected Tropical Disease Research (LCNTDR), Imperial College London, St Mary’s Campus, London, United Kingdom
| | - Timothy J C Anderson
- Disease Intervention and Prevention, Texas Biomedical Research Institute, San Antonio, TX
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Neves MI, Webster JP, Walker M. Estimating helminth burdens using sibship reconstruction. Parasit Vectors 2019; 12:441. [PMID: 31522688 PMCID: PMC6745796 DOI: 10.1186/s13071-019-3687-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Accepted: 08/28/2019] [Indexed: 01/21/2023] Open
Abstract
BACKGROUND Sibship reconstruction is a form of parentage analysis that can be used to identify the number of helminth parental genotypes infecting individual hosts using genetic data on only their offspring. This has the potential to be used for estimating individual worm burdens when adult parasites are otherwise inaccessible, the case for many of the most globally important human helminthiases and neglected tropical diseases. Yet methods of inferring worm burdens from sibship reconstruction data on numbers of unique parental genotypes are lacking, limiting the method's scope of application. RESULTS We developed a novel statistical method for estimating female worm burdens from data on the number of unique female parental genotypes derived from sibship reconstruction. We illustrate the approach using genotypic data on Schistosoma mansoni (miracidial) offspring collected from schoolchildren in Tanzania. We show how the bias and precision of worm burden estimates critically depends on the number of sampled offspring and we discuss strategies for obtaining sufficient sample sizes and for incorporating judiciously formulated prior information to improve the accuracy of estimates. CONCLUSIONS This work provides a novel approach for estimating individual-level worm burdens using genetic data on helminth offspring. This represents a step towards a wider scope of application of parentage analysis techniques. We discuss how the method could be used to assist in the interpretation of monitoring and evaluation data collected during mass drug administration programmes targeting human helminthiases and to help resolve outstanding questions on key population biological processes that govern the transmission dynamics of these neglected tropical diseases.
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Affiliation(s)
- M Inês Neves
- Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hawkshead Lane, Hatfield, UK. .,London Centre for Neglected Tropical Disease Research, London, UK.
| | - Joanne P Webster
- Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hawkshead Lane, Hatfield, UK.,London Centre for Neglected Tropical Disease Research, London, UK
| | - Martin Walker
- Department of Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hawkshead Lane, Hatfield, UK.,London Centre for Neglected Tropical Disease Research, London, UK
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Estimating effective population size for a cestode parasite infecting three-spined sticklebacks. Parasitology 2019; 146:883-896. [PMID: 30720409 DOI: 10.1017/s0031182018002226] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Remarkably few attempts have been made to estimate contemporary effective population size (Ne) for parasitic species, despite the valuable perspectives it can offer on the tempo and pace of parasite evolution as well as coevolutionary dynamics of host-parasite interactions. In this study, we utilized multi-locus microsatellite data to derive single-sample and temporal estimates of contemporary Ne for a cestode parasite (Schistocephalus solidus) as well as three-spined stickleback hosts (Gasterosteus aculeatus) in lakes across Alaska. Consistent with prior studies, both approaches recovered small and highly variable estimates of parasite and host Ne. We also found that estimates of host Ne and parasite Ne were sensitive to assumptions about population genetic structure and connectivity. And, while prior work on the stickleback-cestode system indicates that physiographic factors external to stickleback hosts largely govern genetic variation in S. solidus, our findings indicate that stickleback host attributes and factors internal to the host - namely body length, genetic diversity and infection - shape contemporary Ne of cestode parasites.
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10
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Barbosa LM, Barros BC, de Souza Rodrigues M, Silva LK, Reis MG, Blanton RE. The effect of sample size on estimates of genetic differentiation and effective population size for Schistosoma mansoni populations. Int J Parasitol 2018; 48:1149-1154. [PMID: 30367861 PMCID: PMC6261692 DOI: 10.1016/j.ijpara.2018.10.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 10/04/2018] [Accepted: 10/10/2018] [Indexed: 01/28/2023]
Abstract
Eradication or local extinction of the human parasite Schistosoma mansoni is a goal for many control programs. Population genetic analyses are helping to evaluate and guide these efforts, yet what to sample, how to sample and how densely to sample is not well established. We determined the S. mansoni allele frequency profile of nearly all infected inhabitants in two small Brazilian communities and created sub-samples representing 5-50% of all detected human infections (infrapopulations). Samples were selected at random with replacement, and each size class was replicated 100 times. Mean pairwise differentiation for all infrapopulations (Di) and the variance effective population size (Ne) were calculated for each sample. Prior to community-wide treatment, the true mean Di was moderate (0.095-0.123) and Ne large (>30,000). Most samples of <50% of those infected produced estimates outside of 5% of the true value. For estimates within 10%, sample sizes of >15% of all infrapopulations were required. At the 3 year follow-up after treatment, the Di increased and Ne was reduced by >15 fold. At this time sampling of >30-45% was needed to achieve the same accuracy. Following a second treatment and 4 years from baseline, the Di further increased and Ne decreased with little change in the sampling effort required. Extensive sampling is required for accurate estimates of these important population parameters. Characteristics such as population census size, infection prevalence, the community's treatment history and the degree of infrapopulation differentiation should be taken into account. The intensity of infection was weakly correlated with the ability of a single infrapopulation to represent the component population (Dic), indicating a tendency toward random acquisition of parasite genotypes. This also suggests that targeted sampling from those most heavily infected will better represent the genetic diversity of the whole community than a random sample of infrapopulations.
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Affiliation(s)
- Lúcio M Barbosa
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil; Bahiana School of Medicine and Public Health, Av. Silveira Martins, n° 3386, Salvador, Bahia 41150-100, Brazil
| | - Bruna C Barros
- Bahiana School of Medicine and Public Health, Av. Silveira Martins, n° 3386, Salvador, Bahia 41150-100, Brazil
| | - Moreno de Souza Rodrigues
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Luciano K Silva
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Mitermayer G Reis
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil; Bahiana School of Medicine and Public Health, Av. Silveira Martins, n° 3386, Salvador, Bahia 41150-100, Brazil
| | - Ronald E Blanton
- Center for Global Health and Diseases, Case Western Reserve University, Biomedical Research Building, 2109 Adelbert Rd., Cleveland, OH 44106, USA.
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11
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Le Clec’h W, Chevalier FD, McDew-White M, Allan F, Webster BL, Gouvras AN, Kinunghi S, Tchuenté LAT, Garba A, Mohammed KA, Ame SM, Webster JP, Rollinson D, Emery AM, Anderson TJC. Whole genome amplification and exome sequencing of archived schistosome miracidia. Parasitology 2018; 145:1739-1747. [PMID: 29806576 PMCID: PMC6193844 DOI: 10.1017/s0031182018000811] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Adult schistosomes live in the blood vessels and cannot easily be sampled from humans, so archived miracidia larvae hatched from eggs expelled in feces or urine are commonly used for population genetic studies. Large collections of archived miracidia on FTA cards are now available through the Schistosomiasis Collection at the Natural History Museum (SCAN). Here we describe protocols for whole genome amplification of Schistosoma mansoni and Schistosome haematobium miracidia from these cards, as well as real time PCR quantification of amplified schistosome DNA. We used microgram quantities of DNA obtained for exome capture and sequencing of single miracidia, generating dense polymorphism data across the exome. These methods will facilitate the transition from population genetics, using limited numbers of markers to population genomics using genome-wide marker information, maximising the value of collections such as SCAN.
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Affiliation(s)
- Winka Le Clec’h
- Texas Biomedical Research Institute, Department of Genetics, PO Box 760549, San Antonio, TX 78245-0549, USA
| | - Frédéric D. Chevalier
- Texas Biomedical Research Institute, Department of Genetics, PO Box 760549, San Antonio, TX 78245-0549, USA
| | - Marina McDew-White
- Texas Biomedical Research Institute, Department of Genetics, PO Box 760549, San Antonio, TX 78245-0549, USA
| | - Fiona Allan
- The Natural History Museum, Department of Life Sciences, Cromwell Road, London SW7 5BD, United Kingdom
| | - Bonnie L. Webster
- The Natural History Museum, Department of Life Sciences, Cromwell Road, London SW7 5BD, United Kingdom
| | - Anouk N. Gouvras
- The Natural History Museum, Department of Life Sciences, Cromwell Road, London SW7 5BD, United Kingdom
| | - Safari Kinunghi
- National Institute for Medical Research, Mwanza Research Centre, Mwanza, United Republic of Tanzania
| | - Louis-Albert Tchuem Tchuenté
- Laboratoire de Parasitologie et Ecologie, Université de Yaoundé I, Yaoundé, Cameroon
- Center for Schistosomiasis & Parasitology, P.O. Box 7244, Yaoundé, Cameroon
| | - Amadou Garba
- Réseau International Schistosomoses, Environnement, Aménagement et Lutte (RISEAL-Niger), 333, Avenue des Zarmakoye, B.P. 13724, Niamey, Niger
| | - Khalfan A. Mohammed
- Helminth Control Laboratory Unguja, Ministry of Health, Zanzibar, United Republic of Tanzania
| | - Shaali M. Ame
- Public Health Laboratory - Ivo de Carneri, Pemba, United Republic of Tanzania
| | - Joanne P. Webster
- Centre for Emerging, Endemic and Exotic Diseases, Department of Patholobiology and Population Sciences, Royal Veterinary College, University of London, AL9 7TA, UK United Kingdom
| | - David Rollinson
- The Natural History Museum, Department of Life Sciences, Cromwell Road, London SW7 5BD, United Kingdom
| | - Aidan M. Emery
- The Natural History Museum, Department of Life Sciences, Cromwell Road, London SW7 5BD, United Kingdom
| | - Timothy J. C. Anderson
- Texas Biomedical Research Institute, Department of Genetics, PO Box 760549, San Antonio, TX 78245-0549, USA
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12
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Huo GN, Liu L, He HB, Attwood SW. An investigation into the potential effects of infrapopulation structure and other sources of sampling error, on population genetic studies of the transmission of Schistosoma japonicum (Trematoda: Digenea). Parasit Vectors 2016; 9:165. [PMID: 27000844 PMCID: PMC4802887 DOI: 10.1186/s13071-016-1454-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 03/15/2016] [Indexed: 02/05/2023] Open
Abstract
Background Schistosoma japonicum remains a major challenge to human and animal health. Earlier microsatellite-based studies reported possible definitive-host-specific private alleles within S. japonicum, opening the possibility that different definitive hosts might harbour different parasite strains. Previous investigations have also detected near-identical multilocus genotypes in populations of adult worms - possibly the result of mutations occurring during the asexual (intramolluscan) phase of clonal expansion. Research has also revealed extensive deviations from Hardy-Weinberg Proportions (HWP) and conflicting results among studies. The present study was performed to examine some of the potential effects of infrapopulation structure on microsatellite-based studies of the transmission ecology of S. japonicum. Potential sources of bias considered included organotropic distribution of worms, non-random mating and corrections for clonal expansion. Results Stool samples from naturally infected hosts were used to infect snails in the laboratory and thereby expose mice. 274 individual worms were typed at seven microsatellite loci. Removal of individuals bearing duplicate MLGs (as a correction for presumed clonal expansion) had an impact on both HWP and organotropic genetic differentiation. The study found no evidence that heterozygote deficiencies were caused by a Wahlund effect. Female-male pairings appeared to be random and there was no evidence for mate choice by heterozygosity. There was some indication that excess heterozygosity, induced by clonal expansion, can offset heterozygote deficiencies caused by small population size or populations fragmented by parasite control efforts. Conclusions The view is supported that miracidia are preferable to adult worms in investigations into host-specific parasite lineages. Where adults must be used, extreme care should be taken with regard to sampling if infrapopulations of small animals are compared with those of larger animals; this is because of organotropic patterns in genetic variation and the tendency to sample from different organs in differently sized hosts. As corrections for clones may accentuate signals of population subdivision, corrections should only be made if tests for clonal expansion prove positive. Finally, evidence for heterozygote deficiency caused by small sample size, calls for carefully designed random and comprehensive sampling strategies for S. japonicum in China, where control efforts have greatly fragmented parasite populations. Electronic supplementary material The online version of this article (doi:10.1186/s13071-016-1454-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Guan-Nan Huo
- State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, People's Republic of China
| | - Liang Liu
- State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, People's Republic of China
| | - Hong-Bin He
- Hunan Institute of Parasitic Diseases, Yueyang, Hunan, People's Republic of China
| | - Stephen W Attwood
- State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, People's Republic of China. .,Department of Life Sciences, The Natural History Museum, London, UK.
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13
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Barbosa LM, Reis EA, Dos Santos CRA, Costa JM, Carmo TM, Aminu PT, Pitanga TN, Ponce-Terashima R, Blank WA, Silva LK, Reis MG, Blanton RE. Repeated praziquantel treatments remodel the genetic and spatial landscape of schistosomiasis risk and transmission. Int J Parasitol 2016; 46:343-50. [PMID: 26953255 DOI: 10.1016/j.ijpara.2016.01.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2015] [Revised: 01/25/2016] [Accepted: 01/28/2016] [Indexed: 11/19/2022]
Abstract
Repeated treatments with praziquantel reduce schistosomiasis prevalence and morbidity, but transmission persists and populations often recover within a few years. To identify factors associated with persistence, we surveyed and treated all identified Schistosoma mansoni infections in two rural Brazilian communities (Jenipapo and Volta do Rio) in 2009, 2012 and 2013. Eggs were collected from all infected individuals and genotyped with 11 microsatellite markers to evaluate parasite differentiation and diversity. After successive rounds of community-wide treatment, prevalence decreased from 45% to 24% then 16%. Intensity of infection decreased by 57% over this period, and the number of eggs transmitted to the environment decreased by 92%. During all time periods the majority of eggs were excreted by those >15years of age. The incidence was 23% in 2012 and 15% in 2013, consistent with a decrease in transmission. There was little immigration or gene flow over a distance of 6km. On reinfection, infrapopulations were moderately differentiated indicating that pretreatment multilocus genotypes were not fully reacquired. The effective population size responded to census population decline more rapidly than differentiation. Reinfection was concentrated in the downstream portion of Jenipapo, consistent with the observed increased human fecal contamination. At this scale and in this area S. mansoni infections exist on a fragmented landscape with a highly focal pattern of transmission that may facilitate future elimination.
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Affiliation(s)
- Lúcio M Barbosa
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil; Bahiana School of Medicine and Public Health, Av. Silveira Martins, n° 3386, Salvador, Bahia 41150-100, Brazil
| | - Eliana A Reis
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Cláudio R A Dos Santos
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Jackson M Costa
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Theomira M Carmo
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Peace T Aminu
- Center for Global Health and Diseases, Case Western Reserve University, Biomedical Research Building, 2109 Adelbert Rd., Cleveland, OH 44106, USA
| | - Thassila N Pitanga
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | | | - Walter A Blank
- Center for Global Health and Diseases, Case Western Reserve University, Biomedical Research Building, 2109 Adelbert Rd., Cleveland, OH 44106, USA
| | - Luciano K Silva
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil
| | - Mitermayer G Reis
- Gonçalo Moniz Research Centre, Oswaldo Cruz Foundation, Rua Waldemar Falcão, 121 Brotas, Salvador, Bahia 40296-710, Brazil; Bahiana School of Medicine and Public Health, Av. Silveira Martins, n° 3386, Salvador, Bahia 41150-100, Brazil
| | - Ronald E Blanton
- Center for Global Health and Diseases, Case Western Reserve University, Biomedical Research Building, 2109 Adelbert Rd., Cleveland, OH 44106, USA.
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Modelling the effects of mass drug administration on the molecular epidemiology of schistosomes. ADVANCES IN PARASITOLOGY 2015; 87:293-327. [PMID: 25765198 DOI: 10.1016/bs.apar.2014.12.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
As national governments scale up mass drug administration (MDA) programs aimed to combat neglected tropical diseases (NTDs), novel selection pressures on these parasites increase. To understand how parasite populations are affected by MDA and how to maximize the success of control programmes, it is imperative for epidemiological, molecular and mathematical modelling approaches to be combined. Modelling of parasite population genetic and genomic structure, particularly of the NTDs, has been limited through the availability of only a few molecular markers to date. The landscape of infectious disease research is being dramatically reshaped by next-generation sequencing technologies and our understanding of how repeated selective pressures are shaping parasite populations is radically altering. Genomics can provide high-resolution data on parasite population structure, and identify how loci may contribute to key phenotypes such as virulence and/or drug resistance. We discuss the incorporation of genetic and genomic data, focussing on the recently sequenced Schistosoma spp., into novel mathematical transmission models to inform our understanding of the impact of MDA and other control methods. We summarize what is known to date, the models that exist and how population genetics has given us an understanding of the effects of MDA on the parasites. We consider how genetic and genomic data have the potential to shape future research, highlighting key areas where data are lacking, and how future molecular epidemiology knowledge can aid understanding of transmission dynamics and the effects of MDA, ultimately informing public health policy makers of the best interventions for NTDs.
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15
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No apparent reduction in schistosome burden or genetic diversity following four years of school-based mass drug administration in mwea, central kenya, a heavy transmission area. PLoS Negl Trop Dis 2014; 8:e3221. [PMID: 25299057 PMCID: PMC4191953 DOI: 10.1371/journal.pntd.0003221] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 08/26/2014] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND Schistosomiasis is a debilitating neglected tropical disease that infects over 200 million people worldwide. To combat this disease, in 2012, the World Health Organization announced a goal of reducing and eliminating transmission of schistosomes. Current control focuses primarily on mass drug administration (MDA). Therefore, we monitored transmission of Schistosoma mansoni via fecal egg counts and genetic markers in a typical school based MDA setting to ascertain the actual impacts of MDA on the targeted schistosome population. METHODS For 4 years, we followed 67 children enrolled in a MDA program in Kenya. Infection status and egg counts were measured each year prior to treatment. For 15 of these children, for which there was no evidence of acquired resistance, meaning they became re-infected following each treatment, we collected microsatellite genotype data from schistosomes passed in fecal samples as a representation of the force of transmission between drug treatments. We genotyped a total of 4938 parasites from these children, with an average of 329.2 parasites per child for the entire study, and an average of 82.3 parasites per child per annual examination. We compared prevalence, egg counts, and genetic measures including allelic richness, gene diversity (expected heterozygosity), adult worm burdens and effective number of breeders among time points to search for evidence for a change in transmission or schistosome populations during the MDA program. FINDINGS We found no evidence of reduced transmission or schistosome population decline over the course of the program. Although prevalence declined in the 67 children as it did in the overall program, reinfection rates were high, and for the 15 children studied in detail, schistosome egg counts and estimated adult worm burdens did not decline between years 1 and 4, and genetic diversity increased over the course of drug treatment. INTERPRETATION School based control programs undoubtedly improve the health of individuals; however, our data show that in an endemic area, such a program has had no obvious effect on reducing transmission or of significantly impacting the schistosome population as sampled by the children we studied in depth. Results like these, in combination with other sources of information, suggest more integrated approaches for interrupting transmission and significantly diminishing schistosome populations will be required to achieve sustainable control.
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16
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Chevalier FD, Valentim CLL, LoVerde PT, Anderson TJC. Efficient linkage mapping using exome capture and extreme QTL in schistosome parasites. BMC Genomics 2014; 15:617. [PMID: 25048426 PMCID: PMC4117968 DOI: 10.1186/1471-2164-15-617] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Accepted: 07/14/2014] [Indexed: 12/30/2022] Open
Abstract
Background Identification of parasite genes that underlie traits such as drug resistance and host specificity is challenging using classical linkage mapping approaches. Extreme QTL (X-QTL) methods, originally developed by rodent malaria and yeast researchers, promise to increase the power and simplify logistics of linkage mapping in experimental crosses of schistosomes (or other helminth parasites), because many 1000s of progeny can be analysed, phenotyping is not required, and progeny pools rather than individuals are genotyped. We explored the utility of this method for mapping a drug resistance gene in the human parasitic fluke Schistosoma mansoni. Results We staged a genetic cross between oxamniquine sensitive and resistant parasites, then between two F1 progeny, to generate multiple F2 progeny. One group of F2s infecting hamsters was treated with oxamniquine, while a second group was left untreated. We used exome capture to reduce the size of the genome (from 363 Mb to 15 Mb) and exomes from pooled F2 progeny (treated males, untreated males, treated females, untreated females) and the two parent parasites were sequenced to high read depth (mean = 95-366×) and allele frequencies at 14,489 variants compared. We observed dramatic enrichment of alleles from the resistant parent in a small region of chromosome 6 in drug-treated male and female pools (combined analysis: = 11.07, p = 8.74 × 10-29). This region contains Smp_089320 a gene encoding a sulfotransferase recently implicated in oxamniquine resistance using classical linkage mapping methods. Conclusions These results (a) demonstrate the utility of exome capture for generating reduced representation libraries in Schistosoma mansoni, and (b) provide proof-of-principle that X-QTL methods can be successfully applied to an important human helminth. The combination of these methods will simplify linkage analysis of biomedically or biologically important traits in this parasite. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-617) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | - Timothy J C Anderson
- Department of Genetics, Texas Biomedical Research Institute, P,O, Box 760549, 78245 San Antonio, Texas, USA.
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17
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Van den Broeck F, Meurs L, Raeymaekers JAM, Boon N, Dieye TN, Volckaert FAM, Polman K, Huyse T. Inbreeding within human Schistosoma mansoni: do host-specific factors shape the genetic composition of parasite populations? Heredity (Edinb) 2014; 113:32-41. [PMID: 24619176 DOI: 10.1038/hdy.2014.13] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 01/09/2014] [Accepted: 01/17/2014] [Indexed: 11/09/2022] Open
Abstract
The size, structure and distribution of host populations are key determinants of the genetic composition of parasite populations. Despite the evolutionary and epidemiological merits, there has been little consideration of how host heterogeneities affect the evolutionary trajectories of parasite populations. We assessed the genetic composition of natural populations of the parasite Schistosoma mansoni in northern Senegal. A total of 1346 parasites were collected from 14 snail and 57 human hosts within three villages and individually genotyped using nine microsatellite markers. Human host demographic parameters (age, gender and village of residence) and co-infection with Schistosoma haematobium were documented, and S. mansoni infection intensities were quantified. F-statistics and clustering analyses revealed a random distribution (panmixia) of parasite genetic variation among villages and hosts, confirming the concept of human hosts as 'genetic mixing bowls' for schistosomes. Host gender and village of residence did not show any association with parasite genetics. Host age, however, was significantly correlated with parasite inbreeding and heterozygosity, with children being more infected by related parasites than adults. The patterns may be explained by (1) genotype-dependent 'concomitant immunity' that leads to selective recruitment of genetically unrelated worms with host age, and/or (2) the 'genetic mixing bowl' hypothesis, where older hosts have been exposed to a wider variety of parasite strains than children. The present study suggests that host-specific factors may shape the genetic composition of schistosome populations, revealing important insights into host-parasite interactions within a natural system.
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Affiliation(s)
- F Van den Broeck
- 1] Laboratory of Biodiversity and Evolutionary Genomics, University of Leuven, Leuven, Belgium [2] Unit of Medical Helminthology, Institute of Tropical Medicine, Antwerp, Belgium
| | - L Meurs
- Unit of Medical Helminthology, Institute of Tropical Medicine, Antwerp, Belgium
| | | | - N Boon
- 1] Laboratory of Biodiversity and Evolutionary Genomics, University of Leuven, Leuven, Belgium [2] Unit of Medical Helminthology, Institute of Tropical Medicine, Antwerp, Belgium
| | - T N Dieye
- Laboratory of Bacteriology and Virology, Aristide Le Dantec University Hospital, Dakar, Senegal
| | - F A M Volckaert
- Laboratory of Biodiversity and Evolutionary Genomics, University of Leuven, Leuven, Belgium
| | - K Polman
- Unit of Medical Helminthology, Institute of Tropical Medicine, Antwerp, Belgium
| | - T Huyse
- 1] Laboratory of Biodiversity and Evolutionary Genomics, University of Leuven, Leuven, Belgium [2] Unit of Medical Helminthology, Institute of Tropical Medicine, Antwerp, Belgium [3] Section Invertebrates, Royal Museum for Central Africa, Tervuren, Belgium
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