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Bradbury RS, Pafčo B, Nosková E, Hasegawa H. Strongyloides genotyping: a review of methods and application in public health and population genetics. Int J Parasitol 2021; 51:1153-1166. [PMID: 34757088 DOI: 10.1016/j.ijpara.2021.10.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 10/07/2021] [Accepted: 10/11/2021] [Indexed: 12/12/2022]
Abstract
Strongyloidiasis represents a major medical and veterinary helminthic disease. Human infection is caused by Strongyloides stercoralis, Strongyloides fuelleborni fuelleborni and Strongyloides fuelleborni kellyi, with S.stercoralis accounting for the majority of cases. Strongyloides f. fuelleborni likely represents a zoonosis acquired from non-human primates (NHPs), while no animal reservoir for S. f. kellyi infection has been found. Whether S. stercoralis represents a zoonosis acquired from dogs and cats remains unanswered. Over the past two decades various tools have been applied to genotype Strongyloides spp. The most commonly sequenced markers have been the hyper-variable regions I and IV of the 18S rRNA gene and selected portions of the cytochrome c oxidase subunit I gene. These markers have been sequenced and compared in Strongyloides from multiple hosts and geographical regions. More recently, a machine learning algorithm multi-locus sequence typing approach has been applied using these markers, while others have applied whole genome sequencing. Genotyping of Strongyloides from dogs, cats, NHPs and humans has identified that S. stercoralis likely originated in dogs and adapted to human hosts. It has also been demonstrated that S. stercoralis is distinct from S. f. fuelleborni and S. f. kellyi. Two distinct genetic clades of S. stercoralis exist, one restricted to dogs and another infecting humans, NHPs, dogs and cats. Genotyping of S. f. fuelleborni has identified two separate clades, one associated with African isolates and another Indochinese peninsular clade. This review summarises the history and development of genotyping tools for Strongyloides spp. It describes the findings of major studies to date in the context of the epidemiology and evolutionary biology of these helminths, with a specific focus on human-infecting species.
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Affiliation(s)
- Richard S Bradbury
- Health Innovation and Transformation Centre, Federation University, Berwick, Victoria, Australia.
| | - Barbora Pafčo
- Institute of Vertebrate Biology, The Czech Academy of Sciences, Brno, Czech Republic
| | - Eva Nosková
- Department of Botany and Zoology, Faculty of Science, Masaryk University, Brno, Czech Republic
| | - Hideo Hasegawa
- Department of Biomedicine, Faculty of Medicine, Oita University, Yufu, Oita, Japan
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Eslahi AV, Badri M, Nahavandi KH, Houshmand E, Dalvand S, Riahi SM, Johkool MG, Asadi N, Hoseini Ahangari SA, Taghipour A, Zibaei M, Khademvatan S. Prevalence of strongyloidiasis in the general population of the world: a systematic review and meta-analysis. Pathog Glob Health 2021; 115:7-20. [PMID: 33433291 DOI: 10.1080/20477724.2020.1851922] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Strongyloides stercoralis is a neglected soil-transmitted helminth affects approximately 100-370 million people globally. The life cycle is unusual as only larvae can be found in stool specimens. Thecurrent review and meta-analysis represented the distribution of strongyloidiasis in general population of the world based on published papers. Five English databases (Science Direct, Scopus, PubMed, Web of Science, and Google Scholar(were explored for literature published before October 2019.Altogether 235 studies (862243 participants) was eligible. Regarding diagnostic method, the overall prevalence for studies performed microscopic, culture, immunological and molecular method was 1.47% (95% CI = 1.56%), 10.08% (95% CI = 8.99% - 11.16%), 23.88% (95% CI = 20.82% - 26.94%) and 9.3% (95% CI = 7.2% - 11.3%), respectively. Based on microscopic methods, the highest prevalence was related to the Western Pacific region [9.47% (95% CI = 8.55% - 10.39%)]. According to the culture method, Western Pacific region [21.36% (95% CI = 16.32% - 26.39%)] had the highest estimated pooled prevalence. In immunological studies, Eastern Mediterranean Region [40.72% (95% CI = 36.74% - 44.70%)] had the highest seroprevalence.Also in molecular surveys, the highest prevalence was related to the African region [19.72% (95% CI = 16.71% - 22.73%)]. The current study indicated that strongyloidiasis is still considered a health problem in many parts of the world. Thus a comprehensive control program and improvement of public health sectors are required.
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Affiliation(s)
- Aida Vafae Eslahi
- Student Research Committee, Urmia University of Medical Sciences , Urmia, Iran
| | - Milad Badri
- Metabolic Diseases Research Center, Research Institute for Prevention of Non-Communicable Diseases, Qazvin University of Medical Sciences , Qazvin, Iran
| | | | - Elham Houshmand
- Department of Parasitology, Faculty of veterinary medicine, Rasht Branch, Islamic Azad university , Guilan, Iran
| | - Sahar Dalvand
- Functional Neurosurgery Research Center, Shohada Tajrish Comprehensive Neurosurgical Center of Excellence, Shahid Beheshti University of Medical Sciences , Tehran, Iran
| | - Seyed Mohammad Riahi
- Social Determinants of Health Research Centre, Department of Epidemiology and Biostatistics, School of Health, Birjand University of Medical Sciences , Birjand, Iran
| | - Morteza Ghanbari Johkool
- Metabolic Diseases Research Center, Research Institute for Prevention of Non-Communicable Diseases, Qazvin University of Medical Sciences , Qazvin, Iran
| | - Negar Asadi
- Student Research Committee, Urmia University of Medical Sciences , Urmia, Iran.,Cellular and Molecular Research Center & Department of Medical Parasitology and Mycology, Urmia University of Medical Sciences , Urmia, Iran
| | | | - Ali Taghipour
- Department of Parasitology, Faculty of medical sciences, Tarbiat Modares University , Tehran, Iran
| | - Mohammad Zibaei
- Department of Parasitology and Mycology, School of Medicine, Alborz University of Medical Sciences , Karaj, Iran.,Evidence-based Phytotherapy and Complementary Medicine Research Center, Alborz University of Medical Sciences , Karaj, Iran
| | - Shahram Khademvatan
- Student Research Committee, Urmia University of Medical Sciences , Urmia, Iran.,Cellular and Molecular Research Center & Department of Medical Parasitology and Mycology, Urmia University of Medical Sciences , Urmia, Iran
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Strong-LAMP Assay Based on a Strongyloides spp.-Derived Partial Sequence in the 18S rRNA as Potential Biomarker for Strongyloidiasis Diagnosis in Human Urine Samples. DISEASE MARKERS 2020; 2020:5265198. [PMID: 32566039 PMCID: PMC7281818 DOI: 10.1155/2020/5265198] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 04/24/2020] [Indexed: 01/14/2023]
Abstract
Human strongyloidiasis a soil-transmitted infection caused by Strongyloides stercoralis is one of the most neglected amongst the so-called Neglected Tropical Diseases (NTDs). S. stercoralis is a nematode, which is distributed worldwide; it has been estimated that it could affect millions of people, mainly in tropical and subtropical endemic regions. The difficulties of diagnosis lead to infection rates being underreported. Asymptomatic patients have chronic infections that can lead to severe hyperinfection syndrome or disseminated strongyloidiasis in immunocompromised patients. Strongyloidiasis can easily be misdiagnosed because conventional faecal-based techniques lack of sensitivity for the morphological identification of infective larvae in faeces. None of the currently used molecular methods have used urine samples as an alternative to faecal samples for diagnosing strongyloidiasis. This study was thus aimed at comparing, for the first time, the use of a new loop-mediated isothermal amplification (LAMP) molecular assay (Strong-LAMP) to traditional methods on patients' urine samples. Twenty-four urine samples were taken from patients included in a study involving two Spanish hospitals for strongyloidiasis screening using parasitological and serological tests. Strongyloides larvae were found in 11 patients' faecal samples, thereby ascertaining that they had the disease. Other patients had high antibody titres but no larvae were found in their faeces. All urine samples were analysed by PCR and Strong-LAMP assay. No amplification occurred when using PCR. Strong-LAMP led to detecting S. stercoralis DNA in urine samples from patients having previously confirmed strongyloidiasis by parasitological tests and/or a suspicion of being infected by serological ones. The Strong-LAMP assay is a useful molecular tool for research regarding strongyloidiasis in human urine samples. After further validation, the Strong-LAMP assay could also be used for complementary and effective diagnosis of strongyloidiasis in a clinical setting.
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Abstract
Purpose of Review This paper constitutes an update of recent studies on the general biology, molecular genetics, and cellular biology of Strongyloides spp. and related parasitic nematodes. Recent Findings Increasingly, human strongyloidiasis is considered the most neglected of neglected tropical diseases. Despite this, the last 5 years has seen remarkable advances in the molecular biology of Strongyloides spp. Genome sequences for S. stercoralis, S. ratti, S. venezuelensis, S. papillosus, and the related parasite Parastrongyloides trichosuri were created, annotated, and analyzed. These genomic resources, along with a practical transgenesis platform for Strongyloides spp., aided a major achievement, the advent of targeted mutagenesis via CRISPR/Cas9 in S. stercoralis and S. ratti. The genome sequences have also enabled significant molecular epidemiologic and phylogenetic findings on human strongyloidiasis, including the first genetic evidence of zoonotic transmission of S. stercoralis between dogs and humans. Studies of molecular signaling pathways identified the nuclear receptor Ss-DAF-12 as one that can be manipulated in the parasite by exogenous application of its steroid ligands. The chemotherapeutic implications of this were unscored by a study in which a Ss-DAF-12 ligand suppressed autoinfection by S. stercoralis in a new murine model of human strongyloidiasis. Summary Seminal advances in genomics of Strongyloides spp. have transformed research into strongyloidiasis, facilitating fundamental phylogenetic and epidemiologic studies and aiding the deployment of CRISPR/Cas9 gene disruption and editing as functional genomic tools in Strongyloides spp. Studies of Ss-DAF-12 signaling in S. stercoralis demonstrated the potential of this pathway as a novel chemotherapeutic target in parasitic nematodes.
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Affiliation(s)
- Tegegn G. Jaleta
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - James B. Lok
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA
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de Oliveira Simões R, Simões SBE, Luque JL, Iñiguez AM, Júnior AM. First Record ofRaillietina celebensis(Cestoda: Cyclophyllidea) in South America: Redescription and Phylogeny. J Parasitol 2017; 103:359-365. [DOI: 10.1645/16-139] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Affiliation(s)
- Raquel de Oliveira Simões
- Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Instituto Oswaldo Cruz, Av. Brasil 4365 Manguinhos, 21045-900, Rio de Janeiro, RJ, Brazil
| | - Susana Balmant Enrique Simões
- Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Instituto Oswaldo Cruz, Av. Brasil 4365 Manguinhos, 21045-900, Rio de Janeiro, RJ, Brazil
| | - José Luis Luque
- Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Instituto Oswaldo Cruz, Av. Brasil 4365 Manguinhos, 21045-900, Rio de Janeiro, RJ, Brazil
| | - Alena Mayo Iñiguez
- Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Instituto Oswaldo Cruz, Av. Brasil 4365 Manguinhos, 21045-900, Rio de Janeiro, RJ, Brazil
| | - Arnaldo Maldonado Júnior
- Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Instituto Oswaldo Cruz, Av. Brasil 4365 Manguinhos, 21045-900, Rio de Janeiro, RJ, Brazil
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Toledo R, Muñoz-Antoli C, Esteban JG. Strongyloidiasis with emphasis on human infections and its different clinical forms. ADVANCES IN PARASITOLOGY 2015; 88:165-241. [PMID: 25911368 DOI: 10.1016/bs.apar.2015.02.005] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Strongyloidiasis (caused by Strongyloides stercoralis, and to a lesser extent by Strongyloides fuelleborni) is one of the most neglected tropical diseases with endemic areas and affecting more than 100 million people worldwide. Chronic infections in endemic areas can be maintained for decades through the autoinfective cycle with the L3 filariform larvae. In these endemic areas, misdiagnosis, inadequate treatment and the facilitation of the hyperinfection syndrome by immunosuppression are frequent and contribute to a high mortality rate. Despite the serious health impact of strongyloidiasis, it is a neglected disease and very little is known about this parasite and the disease when compared to other helminth infections. Control of the disease is difficult because of the many gaps in our knowledge of strongyloidiasis. We examine the recent literature on different aspects of strongyloidiasis with emphasis in those aspects that need further research.
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Affiliation(s)
- Rafael Toledo
- Departamento de Parasitología, Universidad de Valencia, Valencia, Spain
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Repetto SA, Alba Soto CD, Cazorla SI, Tayeldin ML, Cuello S, Lasala MB, Tekiel VS, González Cappa SM. An improved DNA isolation technique for PCR detection of Strongyloides stercoralis in stool samples. Acta Trop 2013; 126:110-4. [PMID: 23416126 DOI: 10.1016/j.actatropica.2013.02.003] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 01/28/2013] [Accepted: 02/01/2013] [Indexed: 01/09/2023]
Abstract
Strongyloides stercoralis is a nematode that causes severe infections in immunocompromised patients. The low parasitic burden of chronically infected patients makes diagnosis difficult to achieve by conventional methods. Here, an in-house (IH) method for the isolation of parasite DNA from stools and a PCR assay for the molecular diagnosis of S. stercoralis were optimized. DNA yield and purity improved with the IH method which included a step of incubation of stool samples with a glycine-SDS buffer and mechanical disruption prior to DNA extraction. For the PCR assay, the addition of bovine serum albumin was required to neutralize inhibitors present in stool. The analytical sensitivity of the PCR using DNA as template, isolated with the IH method, was superior to the commercial one. This study demonstrates that a combined method that adds the step of glycine-SDS buffer incubation plus mechanical disruption prior to DNA isolation with the commercial kit increased PCR sensitivity to levels of the IH method. Finally, our assay was tested on 17 clinical samples. With the IH method for DNA isolation, a S. stercoralis specific band was detected by PCR in the first stool sample in all patients (17/17), while with the commercial kit, our S. stercoralis-specific band was only observed in 7 samples. The superior efficiency of the IH and combined methods over the commercial kit was demonstrated when applied to clinical samples with low parasitic burden. These results show that the DNA extraction procedure is a key to increase sensitivity of the S. stercoralis PCR assay in stool samples. The method developed here could help to improve the molecular diagnosis of S. stercoralis.
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Affiliation(s)
- S A Repetto
- Instituto de Investigación en Microbiología y Parasitología Médica (IMPaM), Facultad de Medicina, Universidad de Buenos Aires - CONICET, Paraguay 2155, piso 13, Ciudad Autónoma de Buenos Aires, Argentina.
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The Synthesium Brachycladiidae Odhner, 1905 (Digenea) association with hosts based on nuclear and mitochondrial genes. Parasitol Int 2011; 60:530-3. [DOI: 10.1016/j.parint.2011.08.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 08/02/2011] [Accepted: 08/04/2011] [Indexed: 11/20/2022]
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Genetic analysis of Anisakis typica (Nematoda: Anisakidae) from cetaceans of the northeast coast of Brazil: New data on its definitive hosts. Vet Parasitol 2011; 178:293-9. [DOI: 10.1016/j.vetpar.2011.01.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 12/22/2010] [Accepted: 01/07/2011] [Indexed: 01/27/2023]
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Morphological and molecular characterization of Strongyloides ophidiae (Nematoda, Strongyloididae). J Helminthol 2009; 84:136-42. [DOI: 10.1017/s0022149x09990381] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractThe aim of the present study is to report morphological data from parasitic female, rhabditoid and filarioid larvae, free-living female worms and eggs of Strongyloides ophidiae (Nematoda, Strongyloididae). In addition, a molecular DNA analysis was carried out using a pool of eight S. ophidiae parasitic females. Samples were obtained from the small intestine of Oxyrhopus guibei (Serpentes, Colubridae) collected in the municipality of Lençóis Paulista, State of São Paulo, Brazil. DNA amplification by polymerase chain reaction (PCR) resulted in a 350 bp band for samples containing S. ophidiae and Strongyloides venezuelensis DNA. Strongyloides ophidiae nucleotide sequence analysis showed 98% similarity with Strongyloides procyonis and 97% with Strongyloides cebus, Strongyloides stercoralis, Strongyloides fuelleborni and Strongyloides sp. from snakes.
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Motta MRA, Pinheiro DCSN, Carvalho VL, Viana DDA, Vicente ACP, Iñiguez AM. Gastric lesions associated with the presence of Anisakis spp. Dujardin, 1845 (Nematoda: Anisakidae) in Cetaceans stranded on the coast of Ceara, Brazil. BIOTA NEOTROPICA 2008. [DOI: 10.1590/s1676-06032008000200010] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The gastric compartments of ten cetaceans stranded on the coast of Ceará State, Northeast Brazil were analyzed in this study. Gastric Anisakis spp. was diagnosed in all individuals involved in this study. Parasites and tissue samples were collected during necropsy. The presence of Anisakis parasites showed similar distribution across the three gastric compartments and the majority was free within the gastric lumen. Macroscopically, the lesions were predominantly characterized by the presence of ulcers (60%, 6/10) within the gastric mucosa, occasionally associated with edema and hemorrhage (30%, 3/10). Eight cetaceans (8/10 - 80%) presented gastric microscopic alterations and in 75% (6/8) of these animals, chronic lymphoplasmocytic gastritis was observed with varying degrees of distribution and severity. Additionally, eosinophilic and granulomatous inflammation with giant cells, hemosiderosis, fibrosis and areas of necrosis were associated with location of parasites within the gastric mucosa. In this study, it was shown that the majority of cetaceans with the presence of Anisakis parasites presented macro and microscopic gastric alterations. These nematodes are probably associated with the development of these alterations; however, more pathological approaches are still required.
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Sato H, Suzuki K, Osanai A, Kamiya H, Furuoka H. Identification and characterization of the threadworm, Strongyloides procyonis, from feral raccoons (Procyon lotor) in Japan. J Parasitol 2006; 92:63-8. [PMID: 16629317 DOI: 10.1645/ge-623r.1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Strongyloides procyonis Little, 1966 was detected about 45 years ago in raccoons (Procyon lotor) of southern Louisiana, U.S.A., and was demonstrated experimentally to cause creeping eruption and a short-lived intestinal infection in a healthy human volunteer. After its description and demonstration of its pathogenicity in humans, S. procyonis has not been found in raccoons in North America despite repeated surveys. During a survey on feral raccoons in Japan, S. procyonis parasitic females were identified in 66 (28.3%) of 233 raccoons collected between May 2004 and January 2005. The number of parasitic females recovered from individual raccoons was 1-197 (geomean, 3.2). Both the morphological features and the nucleotide sequences of the small and large subunit ribosomal RNA genes (SSU/LSU rDNA) of S. procyonis closely resembled those of zoonotic Strongyloides stercoralis. The sequences of internal transcribed spacer (ITS)1 and 28S rDNA could differentiate clearly these 2 species. Awareness of S. procyonis in raccoons in North America and other places worldwide where raccoons are introduced and naturalized is important to assess the epidemiological significance of this potentially zoonotic helminth species.
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Affiliation(s)
- Hiroshi Sato
- Department of Parasitology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan.
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Chilton NB. The use of nuclear ribosomal DNA markers for the identification of bursate nematodes (order Strongylida) and for the diagnosis of infections. Anim Health Res Rev 2005; 5:173-87. [PMID: 15984323 DOI: 10.1079/ahr200497] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Many bursate nematodes are of major importance to animal health. Animals are often parasitized by multiple species that differ in their prevalence, relative abundance and/or pathogenicity. Implementation of effective management strategies for these parasites requires reliable methods for their detection in hosts, identification to the species level and measurement of intensity of infection. One major problem is the difficulty of accurately identifying and distinguishing many species of bursate nematode because of the remarkable morphological similarity of their eggs and larvae. The inability to identify, with confidence, individual nematodes (irrespective of their life-cycle stage) to the species level by morphological methods has often led to a search for species-specific genetic markers. Studies over the past 15 years have shown that sequences of the internal transcribed spacers of ribosomal DNA provide useful genetic markers, providing the basis for the development of PCR-based diagnostic tools. Such molecular methods represent powerful tools for studying the systematics, epidemiology and ecology of bursate nematodes and, importantly, for the specific diagnosis of infections in animals and humans, thus contributing to improved control and prevention strategies for these parasites.
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Affiliation(s)
- Neil B Chilton
- Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada.
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Dorris M, Viney ME, Blaxter ML. Molecular phylogenetic analysis of the genus Strongyloides and related nematodes. Int J Parasitol 2002; 32:1507-17. [PMID: 12392916 DOI: 10.1016/s0020-7519(02)00156-x] [Citation(s) in RCA: 174] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Strongyloides spp., parasitic nematodes of humans and many other terrestrial vertebrates, display an unusual heterogonic lifecycle involving alternating parasitic and free-living adult reproductive stages. A number of other genera have similar lifecycles, but their relationships to Strongyloides have not been clarified. We have inferred a phylogeny of 12 species of Strongyloides, Parastrongyloides, Rhabdias and Rhabditophanes using small subunit ribosomal RNA gene (SSU rDNA) sequences. The lineage leading to Strongyloides appears to have arisen within parasites of terrestrial invertebrates. Inferred lifecycle evolution was particularly dynamic within these nematodes. Importantly, the free-living Rhabditophanes sp. KR3021 is placed within a clade of parasitic taxa, suggesting that this species may represent a reversion to a non-parasitic lifecycle. Species within the genus Strongyloides are very closely related, despite the disparity of host species parasitised. The highly pathogenic human parasite Strongyloides fuelleborni kelleyi is not supported as a subspecies of the primate parasite S. fuelleborni fuelleborni, but is most likely derived from a local zoonotic source.
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Affiliation(s)
- Mark Dorris
- Centre for Marine Biodiversity and Biotechnology, Heriot-Watt University, Riccarton, EH14 4AS, Edinburgh, UK
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