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Cheke RA, Little KE, Young S, Walker M, Basáñez MG. Taking the strain out of onchocerciasis? A reanalysis of blindness and transmission data does not support the existence of a savannah blinding strain of onchocerciasis in West Africa. ADVANCES IN PARASITOLOGY 2021; 112:1-50. [PMID: 34024357 DOI: 10.1016/bs.apar.2021.01.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Onchocerciasis (also known as 'river blindness'), is a neglected tropical disease (NTD) caused by the (Simulium-transmitted) filarial nematode Onchocerca volvulus. The occurrence of 'blinding' (savannah) and non-blinding (forest) parasite strains and the existence of corresponding, locally adapted Onchocerca-Simulium complexes were postulated to explain greater blindness prevalence in savannah than in forest foci. As a result, the World Health Organization (WHO) Onchocerciasis Control Programme in West Africa (OCP) focused anti-vectorial and anti-parasitic interventions in savannah endemic areas. In this paper, village-level data on blindness prevalence, microfilarial prevalence, and transmission intensity (measured by the annual transmission potential, the number of infective, L3, larvae per person per year) were extracted from 16 West-Central Africa-based publications, and analysed according to habitat (forest, forest-savannah mosaic, savannah) to test the dichotomous strain hypothesis in relation to blindness. When adjusting for sample size, there were no statistically significant differences in blindness prevalence between the habitats (one-way ANOVA, P=0.68, mean prevalence for forest=1.76±0.37 (SE); mosaic=1.49±0.38; savannah=1.89±0.26). The well-known relationship between blindness prevalence and annual transmission potential for savannah habitats was confirmed and shown to hold for (but not to be statistically different from) forest foci (excluding data from southern Côte d'Ivoire, in which blindness prevalence was significantly lower than in other West African forest communities, but which had been the focus of studies leading to the strain-blindness hypothesis that was accepted by OCP planners). We conclude that the evidence for a savannah blinding onchocerciasis strain in simple contrast with a non-blinding forest strain is equivocal. A re-appraisal of the strain hypothesis to explain patterns of ocular disease is needed to improve understanding of onchocerciasis epidemiology and disease burden estimates in the light of the WHO 2030 goals for onchocerciasis.
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Affiliation(s)
- Robert A Cheke
- Natural Resources Institute, Department of Agriculture, Health & Environment, University of Greenwich at Medway, Kent, United Kingdom; London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom
| | | | - Stephen Young
- Natural Resources Institute, Department of Agriculture, Health & Environment, University of Greenwich at Medway, Kent, United Kingdom
| | - Martin Walker
- London Centre for Neglected Tropical Disease Research, Department of Pathobiology and Populations Sciences, Royal Veterinary College, Hatfield, United Kingdom
| | - Maria-Gloria Basáñez
- London Centre for Neglected Tropical Disease Research (LCNTDR), Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom; MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Faculty of Medicine, School of Public Health, Imperial College London, London, United Kingdom.
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2
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Hedtke SM, Kuesel AC, Crawford KE, Graves PM, Boussinesq M, Lau CL, Boakye DA, Grant WN. Genomic Epidemiology in Filarial Nematodes: Transforming the Basis for Elimination Program Decisions. Front Genet 2020; 10:1282. [PMID: 31998356 PMCID: PMC6964045 DOI: 10.3389/fgene.2019.01282] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 11/21/2019] [Indexed: 11/25/2022] Open
Abstract
Onchocerciasis and lymphatic filariasis are targeted for elimination, primarily using mass drug administration at the country and community levels. Elimination of transmission is the onchocerciasis target and global elimination as a public health problem is the end point for lymphatic filariasis. Where program duration, treatment coverage, and compliance are sufficiently high, elimination is achievable for both parasites within defined geographic areas. However, transmission has re-emerged after apparent elimination in some areas, and in others has continued despite years of mass drug treatment. A critical question is whether this re-emergence and/or persistence of transmission is due to persistence of local parasites-i.e., the result of insufficient duration or drug coverage, poor parasite response to the drugs, or inadequate methods of assessment and/or criteria for determining when to stop treatment-or due to re-introduction of parasites via human or vector movement from another endemic area. We review recent genetics-based research exploring these questions in Onchocerca volvulus, the filarial nematode that causes onchocerciasis, and Wuchereria bancrofti, the major pathogen for lymphatic filariasis. We focus in particular on the combination of genomic epidemiology and genome-wide associations to delineate transmission zones and distinguish between local and introduced parasites as the source of resurgence or continuing transmission, and to identify genetic markers associated with parasite response to chemotherapy. Our ultimate goal is to assist elimination efforts by developing easy-to-use tools that incorporate genetic information about transmission and drug response for more effective mass drug distribution, surveillance strategies, and decisions on when to stop interventions to improve sustainability of elimination.
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Affiliation(s)
- Shannon M. Hedtke
- Department of Physiology, Anatomy and Microbiology, La Trobe University, Bundoora, VIC, Australia
| | - Annette C. Kuesel
- Unicef/UNDP/World Bank/World Health Organization Special Programme for Research and Training in Tropical Diseases (TDR), World Health Organization, Geneva, Switzerland
| | - Katie E. Crawford
- Department of Physiology, Anatomy and Microbiology, La Trobe University, Bundoora, VIC, Australia
| | - Patricia M. Graves
- College of Public Health, Medical and Veterinary Sciences, James Cook University, Cairns, QLD, Australia
| | - Michel Boussinesq
- Unité Mixte Internationale 233 "TransVIHMI", Institut de Recherche pour le Développement (IRD), INSERM U1175, University of Montpellier, Montpellier, France
| | - Colleen L. Lau
- Department of Global Health, Research School of Population Health, Australian National University, Acton, ACT, Australia
| | - Daniel A. Boakye
- Parasitology Department, Noguchi Memorial Institute for Medical Research, Accra, Ghana
| | - Warwick N. Grant
- Department of Physiology, Anatomy and Microbiology, La Trobe University, Bundoora, VIC, Australia
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Choi YJ, Tyagi R, McNulty SN, Rosa BA, Ozersky P, Mafrtin J, Hallsworth-Pepin K, Unnasch TR, Norice CT, Nutman TB, Weil GJ, Fischer PU, Mitreva M. Genomic diversity in Onchocerca volvulus and its Wolbachia endosymbiont. Nat Microbiol 2016; 2:16207. [PMID: 27869792 PMCID: PMC5512550 DOI: 10.1038/nmicrobiol.2016.207] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 09/19/2016] [Indexed: 01/03/2023]
Abstract
Ongoing elimination efforts have altered the global distribution of Onchocerca volvulus, the agent of river blindness, and further population restructuring is expected as efforts continue. Therefore, a better understanding of population genetic processes and their effect on biogeography is needed to support elimination goals. We describe O. volvulus genome variation in 27 isolates from the early 1990s (before widespread mass treatment) from four distinct locales: Ecuador, Uganda, the West African forest and the West African savanna. We observed genetic substructuring between Ecuador and West Africa and between the West African forest and savanna bioclimes, with evidence of unidirectional gene flow from savanna to forest strains. We identified forest:savanna-discriminatory genomic regions and report a set of ancestry informative loci that can be used to differentiate between forest, savanna and admixed isolates, which has not previously been possible. We observed mito-nuclear discordance possibly stemming from incomplete lineage sorting. The catalogue of the nuclear, mitochondrial and endosymbiont DNA variants generated in this study will support future basic and translational onchocerciasis research, with particular relevance for ongoing control programmes, and boost efforts to characterize drug, vaccine and diagnostic targets.
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Affiliation(s)
- Young-Jun Choi
- McDonnell Genome Institute, Washington University in St. Louis, MO, USA
| | - Rahul Tyagi
- McDonnell Genome Institute, Washington University in St. Louis, MO, USA
| | | | - Bruce A. Rosa
- McDonnell Genome Institute, Washington University in St. Louis, MO, USA
| | - Philip Ozersky
- McDonnell Genome Institute, Washington University in St. Louis, MO, USA
| | - John Mafrtin
- McDonnell Genome Institute, Washington University in St. Louis, MO, USA
| | | | - Thomas R. Unnasch
- Global Health Infectious Disease Research Program, Department of Global Health, University of South Florida, Tampa, FL, USA
| | - Carmelle T. Norice
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, MD, USA
| | - Thomas B. Nutman
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, MD, USA
| | - Gary J. Weil
- Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Peter U. Fischer
- Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Makedonka Mitreva
- McDonnell Genome Institute, Washington University in St. Louis, MO, USA
- Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine, St. Louis, MO, USA
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4
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Crainey JL, Silva TRRD, Encinas F, Marín MA, Vicente ACP, Luz SLB. The mitogenome of Onchocerca volvulus from the Brazilian Amazonia focus. Mem Inst Oswaldo Cruz 2016; 111:79-81. [PMID: 26814648 PMCID: PMC4727440 DOI: 10.1590/0074-02760150350] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 11/19/2015] [Indexed: 12/02/2022] Open
Abstract
We report here the first complete mitochondria genome of Onchocerca
volvulus from a focus outside of Africa. An O. volvulus
mitogenome from the Brazilian Amazonia focus was obtained using a combination of
high-throughput and Sanger sequencing technologies. Comparisons made between this
mitochondrial genome and publicly available mitochondrial sequences identified 46
variant nucleotide positions and suggested that our Brazilian mitogenome is more
closely related to Cameroon-origin mitochondria than West African-origin
mitochondria. As well as providing insights into the origins of Latin American
onchocerciasis, the Brazilian Amazonia focus mitogenome may also have value as an
epidemiological resource.
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Affiliation(s)
- James L Crainey
- Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, Instituto Leônidas e Maria Deane, Fundação Oswaldo Cruz, Manaus, AM, Brasil
| | - Túllio R R da Silva
- Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, Instituto Leônidas e Maria Deane, Fundação Oswaldo Cruz, Manaus, AM, Brasil
| | - Fernando Encinas
- Laboratório de Genética Molecular de Microorganismos, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brasil
| | - Michel A Marín
- Laboratório de Genética Molecular de Microorganismos, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brasil
| | - Ana Carolina P Vicente
- Laboratório de Genética Molecular de Microorganismos, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Brasil
| | - Sérgio L B Luz
- Laboratório de Ecologia de Doenças Transmissíveis na Amazônia, Instituto Leônidas e Maria Deane, Fundação Oswaldo Cruz, Manaus, AM, Brasil
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Jabbar A, Beveridge I, Mohandas N, Chilton NB, Littlewood DTJ, Jex AR, Gasser RB. Analyses of mitochondrial amino acid sequence datasets support the proposal that specimens of Hypodontus macropi from three species of macropodid hosts represent distinct species. BMC Evol Biol 2013; 13:259. [PMID: 24261823 PMCID: PMC4222732 DOI: 10.1186/1471-2148-13-259] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 11/19/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Hypodontus macropi is a common intestinal nematode of a range of kangaroos and wallabies (macropodid marsupials). Based on previous multilocus enzyme electrophoresis (MEE) and nuclear ribosomal DNA sequence data sets, H. macropi has been proposed to be complex of species. To test this proposal using independent molecular data, we sequenced the whole mitochondrial (mt) genomes of individuals of H. macropi from three different species of hosts (Macropus robustus robustus, Thylogale billardierii and Macropus [Wallabia] bicolor) as well as that of Macropicola ocydromi (a related nematode), and undertook a comparative analysis of the amino acid sequence datasets derived from these genomes. RESULTS The mt genomes sequenced by next-generation (454) technology from H. macropi from the three host species varied from 13,634 bp to 13,699 bp in size. Pairwise comparisons of the amino acid sequences predicted from these three mt genomes revealed differences of 5.8% to 18%. Phylogenetic analysis of the amino acid sequence data sets using Bayesian Inference (BI) showed that H. macropi from the three different host species formed distinct, well-supported clades. In addition, sliding window analysis of the mt genomes defined variable regions for future population genetic studies of H. macropi in different macropodid hosts and geographical regions around Australia. CONCLUSIONS The present analyses of inferred mt protein sequence datasets clearly supported the hypothesis that H. macropi from M. robustus robustus, M. bicolor and T. billardierii represent distinct species.
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Affiliation(s)
- Abdul Jabbar
- Faculty of Veterinary Science, The University of Melbourne, Parkville, Melbourne, Victoria 3010, Australia.
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Ardelli BF, Prichard RK. Identification of variant ABC-transporter genes amongOnchocerca volvuluscollected from ivermectin-treated and untreated patients in Ghana, West Africa. ANNALS OF TROPICAL MEDICINE AND PARASITOLOGY 2013; 98:371-84. [PMID: 15228718 DOI: 10.1179/000349804225003415] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Treatment with ivermectin (IVM) is known to cause a loss of polymorphism at certain loci of the beta-tubulin, gamma-aminobutyric-acid-receptor, glutamate-gated-chloride-channel and ATP-binding-cassette (ABC) transporter genes of IVM-resistant Haemonchus contortus. The genetic variation of four ABC-transporter homologues from Onchocerca volvulus was therefore investigated, to determine if any change in genetic polymorphism occurs in these genes following repeated treatment with IVM. Samples were collected in the Northern, Brong-Ahafo and Volta regions of Ghana, in 1999 and 2002; nodules containing adult O. volvulus were removed from subjects who had either received multiple IVM treatments or never taken IVM. The ATP-binding domains of four ABC-transporter genes (OvMDR-1, OvMDR-3, OvABC-1 and OvABC-6) were amplified from individual O. volvulus and examined for polymorphism, using single-strand-conformation-polymorphism (SSCP) analysis. In the samples collected in 1999, OvMDR-1 and OvABC-1 showed significant reduction in polymorphism following IVM treatment whereas OvABC-6 and OvMDR-3 were not found to be polymorphic. The samples collected in 2002 also showed a reduction in polymorphism for both OvMDR-1 and OvABC-1. Several single-nucleotide polymorphisms, which resulted in either amino-acid-replacement substitutions or nonsense mutations, were identified in the alleles of OvMDR-1 and OvABC-1.
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Affiliation(s)
- B F Ardelli
- Institute of Parasitology, McGill University, 21-111 Lakeshore Road, Ste. Anne de Bellevue, Quebec H9X 3V9, Canada
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7
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Cheke RA, Garms R. Indices of onchocerciasis transmission by different members of the Simulium damnosum complex conflict with the paradigm of forest and savanna parasite strains. Acta Trop 2013; 125:43-52. [PMID: 22995985 DOI: 10.1016/j.actatropica.2012.09.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2012] [Revised: 08/29/2012] [Accepted: 09/05/2012] [Indexed: 11/18/2022]
Abstract
Onchocerciasis in savanna zones is generally more severe than in the forest and pathologies also differ geographically, differences often ascribed to the existence of two or more strains and incompatibilities between vectors and strains. However, flies in the forest transmit more infective larvae than their savanna counterparts, even in sympatry, contradicting expectations based on the forest and savanna strains paradigm. We analysed data on the numbers of Onchocerca volvulus larvae of different stages found in 10 different taxonomic categories of the Simulium damnosum complex derived from more than 48,800 dissections of flies from Sierra Leone in the west of Africa to Uganda in the east. The samples were collected before widespread ivermectin distribution and thus provide a baseline for evaluating control measures. Savanna species contained fewer larvae per infected or per infective fly than the forest species, even when biting and parous rates were accounted for. The highest transmission indices were found in the forest-dwelling Pra form of Simulium sanctipauli (616 L3/1000 parous flies) and the lowest in the savanna-inhabiting species S. damnosum/S. sirbanum (135) and S. kilibanum (65). Frequency distributions of numbers of L1-2 and L3 larvae found in parous S. damnosum/S. sirbanum, S. kilibanum, S. squamosum, S. yahense, S. sanctipauli, S. leonense and S. soubrense all conformed to the negative binomial distribution, with the mainly savanna-dwelling species (S. damnosum/S. sirbanum) having less overdispersed distributions than the mainly forest-dwelling species. These infection patterns were maintained even when forest and savanna forms were sympatric and biting the same human population. Furthermore, for the first time, levels of blindness were positively correlated with infection intensities of the forest vector S. yahense, consistent with relations previously reported for savanna zones. Another novel result was that conversion rates of L1-2 larvae to L3s were equivalent for both forest and savanna vectors. We suggest that either a multiplicity of factors are contributing to the observed disease patterns or that many parasite strains exist within a continuum.
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Affiliation(s)
- Robert A Cheke
- Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Chatham, Kent ME4 4TB, UK.
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8
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Sereda MJ, Hartmann S, Büttner DW, Volkmer R, Hovestädt M, Brattig N, Lucius R. Characterization of the allergen filarial tropomyosin with an invertebrate specific monoclonal antibody. Acta Trop 2010; 116:61-7. [PMID: 20525500 DOI: 10.1016/j.actatropica.2010.05.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 05/25/2010] [Accepted: 05/27/2010] [Indexed: 10/19/2022]
Abstract
Tropomyosins of invertebrates are pan-allergens responsible for wide spread allergic reactions against seafood and arthropods. As invertebrate tropomyosins are highly conserved, helminth tropomyosins are likely to show properties similar to these medically important allergens. Studies with a monoclonal antibody, NR1, raised against tropomyosin of the rodent filarial nematode Acanthocheilonema viteae revealed a B cell epitope common to helminths and marine mollusks, which does not occur in vertebrate tropomyosin. This antibody detected tropomyosin of A. viteae, other filariids, nematodes, trematodes and a cestode, and recognized as well tropomyosin of oyster, squid and octopus, but not of arthropods and vertebrates. Immunohistological analyses of A. viteae, Onchocerca volvulus and other nematodes using NR1 showed that tropomyosin is located in the fibrillar part of the body wall muscles and the uterus, and is also conspicuous in muscles of the pharynx, the vagina and other organs of the nematodes. The abundance of a pan-allergen like tropomyosin in parasitic worms and the counterintuitive, but well documented protection against allergic reactivity by some chronic helminth infections is discussed.
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9
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Jex AR, Hu M, Littlewood DTJ, Waeschenbach A, Gasser RB. Using 454 technology for long-PCR based sequencing of the complete mitochondrial genome from single Haemonchus contortus (Nematoda). BMC Genomics 2008; 9:11. [PMID: 18190685 PMCID: PMC2254599 DOI: 10.1186/1471-2164-9-11] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Accepted: 01/11/2008] [Indexed: 11/17/2022] Open
Abstract
Background Mitochondrial (mt) genomes represent a rich source of molecular markers for a range of applications, including population genetics, systematics, epidemiology and ecology. In the present study, we used 454 technology (or the GS20, massively parallel picolitre reactor platform) to determine the complete mt genome of Haemonchus contortus (Nematoda: Trichostrongylidae), a parasite of substantial agricultural, veterinary and economic significance. We validate this approach by comparison with mt sequences from publicly available expressed sequence tag (EST) and genomic survey sequence (GSS) data sets. Results The complete mt genome of Haemonchus contortus was sequenced directly from long-PCR amplified template utilizing genomic DNA (~20–40 ng) from a single adult male using 454 technology. A single contig was assembled and compared against mt sequences mined from publicly available EST (NemBLAST) and GSS datasets. The comparison demonstrated that the 454 technology platform is reliable for the sequencing of AT-rich mt genomes from nematodes. The mt genome sequenced for Haemonchus contortus was 14,055 bp in length and was highly AT-rich (78.1%). In accordance with other chromadorean nematodes studied to date, the mt genome of H. contortus contained 36 genes (12 protein coding, 22 tRNAs, rrnL and rrnS) and was similar in structure, size and gene arrangement to those characterized previously for members of the Strongylida. Conclusion The present study demonstrates the utility of 454 technology for the rapid determination of mt genome sequences from tiny amounts of DNA and reveals a wealth of mt genomic data in current databases available for mining. This approach provides a novel platform for high-throughput sequencing of mt genomes from nematodes and other organisms.
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Affiliation(s)
- Aaron R Jex
- Department of Veterinary Science, The University of Melbourne, 250 Princes Highway, Werribee, Victoria, 3030, Australia.
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10
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Ardelli BF, Prichard RK. Reduced genetic variation of an Onchocerca volvulus ABC transporter gene following treatment with ivermectin. Trans R Soc Trop Med Hyg 2007; 101:1223-32. [PMID: 17904599 DOI: 10.1016/j.trstmh.2005.03.019] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2004] [Revised: 03/09/2005] [Accepted: 03/09/2005] [Indexed: 11/23/2022] Open
Abstract
In some trichostrongyloid nematodes, the early stages of ivermectin (IVM) resistance have been characterized by a shift in allele frequency and reduced polymorphism at loci of P-glycoprotein genes, glutamate-gated chloride channel genes and gamma-aminobutyric acid receptor genes. Mass treatment with IVM is an integral component of the onchocerciasis control programmes. Genetic variation of an Onchocerca volvulus ABC transporter homologue (OvABC-3) from several populations in Africa was examined to determine whether an association exists between alleles of this gene and IVM treatment. Allelic variation in a non-treated population from Ghana showed this locus to be highly polymorphic. However, variability was reduced in IVM-treated populations. chi2 analysis of polymorph frequencies showed significant differences between untreated and treated samples collected in Ghana in 1999. There was less variability in this gene in samples collected in 2002 compared with the 1999 samples. In some treated populations, there appeared to be selection on OvABC-3-C. The observed reduction in variability could be expected in a control programme in which prevalence and intensity of infections are markedly reduced after years of vector control and IVM distribution. The reduction in polymorphism may not in itself indicate that these O. volvulus are IVM resistant, although it could indicate that selection for resistance is occurring.
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Affiliation(s)
- B F Ardelli
- Institute of Parasitology, Macdonald Campus, McGill University, 21 111 Lakeshore Road, Ste. Anne de Bellevue, Quebec H9X 3V9, Canada
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Krueger A, Fischer P, Morales-Hojas R. Molecular phylogeny of the filaria genus Onchocerca with special emphasis on Afrotropical human and bovine parasites. Acta Trop 2007; 101:1-14. [PMID: 17174932 DOI: 10.1016/j.actatropica.2006.11.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2006] [Revised: 11/10/2006] [Accepted: 11/14/2006] [Indexed: 10/23/2022]
Abstract
Filarial parasites of the genus Onchocerca are found in a broad spectrum of ungulate hosts. One species, O. volvulus, is a human parasite that can cause severe disease (onchocerciasis or 'river blindness'). The phylogenetic relationships and the bionomics of many of the nearly 30 known species remain dubious. Here, the phylogeny of 11 species representing most major lineages of the genus is investigated by analysing DNA sequences from three mitochondrial genes (ND5, 12S and 16S rRNA) and portions of the intergenic spacer of the nuclear 5s rRNA. Special emphasis is given to a clade containing a yet unassigned specimen from Uganda (O. sp. 'Siisa'), which appears to be intermediate between O. volvulus and O. ochengi. While the latter can be differentiated by the O-150 tandem repeat commonly used for molecular diagnostics, O. volvulus and O. sp.'Siisa' cannot be differentiated by this marker. In addition, a worm specimen from an African bushbuck appears to be closely related to the bovine O. dukei and represents the basal taxon of the human/bovine clade. At the base of the genus, our data suggest O. flexuosa (red deer), O. ramachandrini (warthog) and O. armillata (cow) to be the representatives of ancient lineages. The results provide better insight into the evolution and zoogeography of Onchocerca. They also have epidemiological and taxonomic implications by providing a framework for more accurate molecular diagnosis of filarial larvae in vectors.
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MESH Headings
- Africa South of the Sahara
- Animals
- Base Sequence
- Cattle
- Cattle Diseases/parasitology
- DNA, Helminth/chemistry
- DNA, Helminth/genetics
- DNA, Mitochondrial/chemistry
- DNA, Mitochondrial/genetics
- Humans
- Molecular Sequence Data
- NADH Dehydrogenase/chemistry
- NADH Dehydrogenase/genetics
- Onchocerca/classification
- Onchocerca/genetics
- Onchocerciasis/parasitology
- Onchocerciasis/veterinary
- Phylogeny
- Polymerase Chain Reaction
- RNA, Ribosomal/chemistry
- RNA, Ribosomal/genetics
- RNA, Ribosomal, 16S/chemistry
- RNA, Ribosomal, 16S/genetics
- Sequence Alignment
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Affiliation(s)
- A Krueger
- Department of Molecular Parasitology, and Federal Forces Department for Tropical Medicine at the Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Str. 74, D-20359 Hamburg, Germany.
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12
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Udall DN. Recent updates on onchocerciasis: diagnosis and treatment. Clin Infect Dis 2006; 44:53-60. [PMID: 17143815 DOI: 10.1086/509325] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2006] [Accepted: 07/31/2006] [Indexed: 11/03/2022] Open
Abstract
Recent progress in onchocerciasis research has led to improved understanding of the immunopathology of Onchocerca volvulus, as well as improvements in diagnosis and treatment of this morbid disease. This article reviews the recent literature, highlighting breakthroughs in sensitive means of antigen testing and an unusual new approach to therapy that targets an endosymbiotic bacterium required for filarial worm fecundity.
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Affiliation(s)
- Don N Udall
- University of California-San Diego, Dermatology Clinical Trials Unit, La Jolla, CA 92037-1300, USA.
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Cutter AD, Félix MA, Barrière A, Charlesworth D. Patterns of nucleotide polymorphism distinguish temperate and tropical wild isolates of Caenorhabditis briggsae. Genetics 2006; 173:2021-31. [PMID: 16783011 PMCID: PMC1569728 DOI: 10.1534/genetics.106.058651] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Caenorhabditis briggsae provides a natural comparison species for the model nematode C. elegans, given their similar morphology, life history, and hermaphroditic mode of reproduction. Despite C. briggsae boasting a published genome sequence and establishing Caenorhabditis as a model genus for genetics and development, little is known about genetic variation across the geographic range of this species. In this study, we greatly expand the collection of natural isolates and characterize patterns of nucleotide variation for six loci in 63 strains from three continents. The pattern of polymorphisms reveals differentiation between C. briggsae strains found in temperate localities in the northern hemisphere from those sampled near the Tropic of Cancer, with diversity within the tropical region comparable to what is found for C. elegans in Europe. As in C. elegans, linkage disequilibrium is pervasive, although recombination is evident among some variant sites, indicating that outcrossing has occurred at a low rate in the history of the sample. In contrast to C. elegans, temperate regions harbor extremely little variation, perhaps reflecting colonization and recent expansion of C. briggsae into northern latitudes. We discuss these findings in relation to their implications for selection, demographic history, and the persistence of self-fertilization.
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Affiliation(s)
- Asher D Cutter
- Institute of Evolutionary Biology, University of Edinburgh, UK.
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14
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Morgan JAT, Dejong RJ, Adeoye GO, Ansa EDO, Barbosa CS, Brémond P, Cesari IM, Charbonnel N, Corrêa LR, Coulibaly G, D'Andrea PS, De Souza CP, Doenhoff MJ, File S, Idris MA, Incani RN, Jarne P, Karanja DMS, Kazibwe F, Kpikpi J, Lwambo NJS, Mabaye A, Magalhães LA, Makundi A, Moné H, Mouahid G, Muchemi GM, Mungai BN, Séne M, Southgate V, Tchuenté LAT, Théron A, Yousif F, Zanotti-Magalhães EM, Mkoji GM, Loker ES. Origin and diversification of the human parasite Schistosoma mansoni. Mol Ecol 2005; 14:3889-902. [PMID: 16202103 DOI: 10.1111/j.1365-294x.2005.02709.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Schistosoma mansoni is the most widespread of the human-infecting schistosomes, present in 54 countries, predominantly in Africa, but also in Madagascar, the Arabian Peninsula, and the Neotropics. Adult-stage parasites that infect humans are also occasionally recovered from baboons, rodents, and other mammals. Larval stages of the parasite are dependent upon certain species of freshwater snails in the genus Biomphalaria, which largely determine the parasite's geographical range. How S. mansoni genetic diversity is distributed geographically and among isolates using different hosts has never been examined with DNA sequence data. Here we describe the global phylogeography of S. mansoni using more than 2500 bp of mitochondrial DNA (mtDNA) from 143 parasites collected in 53 geographically widespread localities. Considerable within-species mtDNA diversity was found, with 85 unique haplotypes grouping into five distinct lineages. Geographical separation, and not host use, appears to be the most important factor in the diversification of the parasite. East African specimens showed a remarkable amount of variation, comprising three clades and basal members of a fourth, strongly suggesting an East African origin for the parasite 0.30-0.43 million years ago, a time frame that follows the arrival of its snail host. Less but still substantial variation was found in the rest of Africa. A recent colonization of the New World is supported by finding only seven closely related New World haplotypes which have West African affinities. All Brazilian isolates have nearly identical mtDNA haplotypes, suggesting a founder effect from the establishment and spread of the parasite in this large country.
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Affiliation(s)
- Jess A T Morgan
- Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131 USA
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15
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Abstract
There are strong biological, evolutionary and immunological arguments for predicting extensive polymorphism among helminth parasites, but relatively little data and few instances from which the selective forces acting on parasite diversity can be discerned. The paucity of information on intraspecific variation stands in contrast to the fine detail with which helminth species have been delineated by morphological techniques, accentuating a trend towards considering laboratory strains as representative of a relatively invariant organism. However, in the fast-moving evolutionary race between host and parasite one would predict a monomorphic species would be driven to extinction. We review the arena of intraspecific variation for the major helminth parasites, ranging from biological properties such as host or vector preference, to biochemical and immunological characteristics, as well as molecular markers such as DNA sequence variants. These data are summarized, before focusing in more detail on polymorphisms within protein-coding genes of potential relevance to the host-parasite relationship, such as vaccine candidates. In particular, we discuss the available data on a number of major antigens from the filarial nematode Brugia malayi. Information is currently too sparse to answer the question of whether there is antigenic variation in filariasis, but the indications are that proteins from the blood-borne microfilarial stage show significant intraspecific variability. Future work will define whether polymorphisms in these antigens may be driven by exposure to the host immune response or reflect some other facet of parasite biology.
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Affiliation(s)
- R M Maizels
- Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh E119 3JT, UK.
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16
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Abstract
Microsatellite deoxyribonucleic acid repeats provide a source of high variability that makes them ideal for use in studies requiring such molecular markers, including large population studies and genetic typing of individuals for kinship investigations. This paper provides reviews of the use of such markers in parasitology. Most studies to date have been carried out using protozoan and vector species. Recent investigations have, however, demonstrated their usefulness in the study of helminths, illustrating their ability to distinguish between individuals within hosts as well as from different hosts. The detection of microsatellites within parasites has provided a tool that will prove invaluable in parasitology and should lead to significant advances in our understanding of the processes that affect the organisms' population genetic structure.
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Affiliation(s)
- G C Barker
- Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, UK.
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Williams SA, Laney SJ, Lizotte-Waniewski M, Ann Bierwert L, Unnasch TR. The River Blindness Genome Project. Trends Parasitol 2002. [DOI: 10.1016/s1471-4922(01)02197-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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18
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Abstract
Genetic diversity in nematodes leads to variation in response to anthelmintics. Haemonchus contortus shows enormous genetic diversity, allowing anthelmintic resistance alleles to be rapidly selected. Anthelmintic resistance is now a widespread problem, especially in H. contortus. Here, I compare the genes involved in anthelmintic resistance in H. contortus with those that confer susceptibility or resistance on the free living nematode Caenorhabditis elegans. I also discuss the latest knowledge of genes associated with resistance to benzimidazoles, levamisole and the macrocyclic lactones and the need for DNA markers for anthelmintic resistance.
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Affiliation(s)
- R Prichard
- Institute of Parasitology, McGill University, H9X 3V9, Montreal, Canada.
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Le TH, Blair D, McManus DP. Mitochondrial genomes of human helminths and their use as markers in population genetics and phylogeny. Acta Trop 2000; 77:243-56. [PMID: 11114386 DOI: 10.1016/s0001-706x(00)00157-1] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
To date, over 100 complete metazoan mitochondrial (mt) genomes of different phyla have been reported. Here, we briefly summarise mt gene organisation in the Metazoa and review what is known of the mt genomes of nematodes and flatworms parasitic in humans. The availability of complete or almost complete mtDNA sequences for several parasitic helminths provides a rich source of genetic markers for phylogenetic analysis and study of genetic variability in helminth groups. Examples of the application of mtDNA in studies on Ascaris, Onchocerca, Schistosoma, Fasciola, Paragonimus, Echinostoma, Echinococcus and Taenia are described.
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Affiliation(s)
- T H Le
- Molecular Parasitology Unit, Australian Centre for International and Tropical Health and Nutrition, The Queensland Institute of Medical Research and The University of Queensland, 300 Herston Road, Qld 4029, Brisbane, Australia
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Mackenzie CD. Human onchocerciasis: the essential partnership between research and disease control efforts. Curr Opin Infect Dis 2000; 13:457-464. [PMID: 11964814 DOI: 10.1097/00001432-200010000-00005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Twenty years ago onchocerciasis was a disease generally ignored by the medical world, except by those who actually worked with the affected people in Africa and Latin America. Now, largely as a result of the success of mass vector control and drug treatment programs, this is a disease management model for developing countries. The recent literature on onchocerciasis has, not surprisingly, mainly focused on various aspects of control. Investigation into the more basic questions is needed to ensure continued effective disease control. The present mass drug control program is based on a single pharmaceutical, ivermectin (Mectizan), which acts almost exclusively on the microfilarial stage of the infection. Efforts are being made to identify other useful drugs; however, no major candidates have yet appeared. The identification of potential biochemical targets for anti-filarial compounds through a better understanding of the biochemistry of these worms is being pursued. The Onchocerca volvulus endosymbiont Wolbachia may provide a target for therapeutic intervention. An improved understanding of the genomics of O. volvulus has made possible the identification of strain differences in the parasites, and an appreciation of the relevance of these strain differences to the clinical disease, onchocerciasis. There is a need for a better understanding of the clinical disease, and the various pathogenic mechanisms that underly the different syndromes. It is particularly important to understand the pathological basis and mechanisms underlying the adverse responses that can occur with chemotherapy. Present control programs now need to be carefully monitored for effectiveness using new assessment tools, such as antigen assays and the identification of organisms in pools of vectors. Current efforts to control onchocerciasis must be coordinated with new chemotherapy-based control programs for other worm diseases that are emerging. The results of laboratory studies are increasingly being applied to improve the effectiveness of field-based control programs and their assessment. Such research is essential for progress towards the goals of controlling and eliminating onchocerciasis.
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Abstract
Onchocerca volvulus, the filarial parasite that causes onchocerciasis or river blindness, contains three distinct genomes. These include the nuclear genome, the mitochondrial genome and the genome of an intracellular endosymbiont of the genus Wolbachia. The nuclear genome is roughly 1.5x10(8) bp in size, and is arranged on four chromosome pairs. Analysis of expressed sequence tags from different life-cycle stages has resulted in the identification of transcripts from roughly 4000 O. volvulus genes. Several of these transcripts are highly abundant, including those encoding collagen and cuticular proteins. Analysis of several gene sequences from O. volvulus suggests that the nuclear genes of O. volvulus are relatively compact and are interrupted relatively frequently by small introns. The intron-exon boundaries of these genes generally follow the GU-AG rule characteristic of the splice donor and acceptors of other vertebrate organisms. The nuclear genome also contains at least one repeated sequence family of a 150 bp repeat which is arranged in tandem arrays and appears subject to concerted evolution. The mitochondrial genome of O. volvulus is remarkably compact, only 13747 bp in size. Consistent with the small size of the genome, four gene pairs overlap, eight contain no intergenic regions and the remaining gene pairs are separated by small intergenic domains ranging from 1 to 46 bp. The protein-coding genes of the O. volvulus mitochondrial genome exhibit a striking codon bias, with 15/20 amino acids having a single codon preference greater than 70%. Intraspecific variation in both the nuclear and mitochondrial genomes appears to be quite limited, consistent with the hypothesis that O. volvulus has suffered a genetic bottleneck in the recent past.
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Affiliation(s)
- T R Unnasch
- Division of Geographic Medicine, University of Alabama at Birmingham, 35294, USA.
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