Article

Mitochondrial genomes of human helminths and their use as markers in population genetics and phylogeny.

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.
Acta Tropica (Impact Factor: 2.52). 01/2001; 77(3):243-56. DOI: 10.1016/S0001-706X(00)00157-1
Source: PubMed

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.

0 Followers
 · 
87 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: It is important to determine the origins of human parasites if we are to understand the health of past populations and the effects of parasitism upon human evolution. It also helps us to understand emerging infectious diseases and the modern clinical epidemiology of parasites. This study aims to distinguish those heirloom parasites that have infected humans and their ancestors throughout their evolution in Africa from those recent souvenir species to which humans have only become exposed following contact with animals during their migration across the globe. Ten such heirloom parasites are proposed, which appear to have been spread across the globe. Six further heirlooms are noted to have limited spread due to the constraints of their life cycle. Twelve souvenir parasites of humans are described, along with their animal reservoirs. While the origins of 28 species of endoparasite have been determined, many more species require further assessment once a more systematic analysis of ancient parasites in other regions of Africa has been undertaken.
    09/2013; 3:191-98. DOI:10.1016/j.ijpp.2013.08.003
  • [Show abstract] [Hide abstract]
    ABSTRACT: Adult tapeworms of the genus Echinococcus (family Taeniidae) occur in the small intestines of carnivorous definitive hosts and are transmitted to particular intermediate mammalian hosts, in which they develop as fluid-filled larvae (cysts) in internal organs (usually lung and liver), causing the disease echinococcosis. Echinococcus species are of major medical importance and also cause losses to the meat and livestock industries, mainly due to the condemnation of infected offal. Decisions regarding the treatment and control of echinococcosis rely on the accurate identification of species and population variants (strains). Conventional, phenetic methods for specific identification have some significant limitations. Despite advances in the development of molecular tools, there has been limited application of mutation scanning methods to species of Echinococcus. Here, we briefly review key genetic markers used for the identification of Echinococcus species and techniques for the analysis of genetic variation within and among populations, and the diagnosis of echinococcosis. We also discuss the benefits of utilizing mutation scanning approaches to elucidate the population genetics and epidemiology of Echinococcus species. These benefits are likely to become more evident following the complete characterization of the genomes of E. granulosus and E. multilocularis.
    Electrophoresis 07/2013; 34(13):1852-62. DOI:10.1002/elps.201300078 · 3.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Stafford in 1905 established the genus Glypthelmins to include Distomum quietum, species collected and described by himself in 1900 as a parasite of anurans from Canada. Since this time, about 36 species parasitizing apodes and anurans have been described around the world, most of them from American continent. Nowadays, there is not a general agreement about the number of species included in Glypthelmins, because some of them have been included in genera such as: Margeana, Haplometrana, Choledocystus, Microderma, Repandum, Rauschiella, Reynoldstrema e Hylotrema. Different taxonomic studies have considered some of these genera as synonyms of Glypthelmins or as valid genera. Nevertheless, the taxonomic classification has never been based on a phylogenetic hypothesis and in consequence the monophyly of the group has not been demonstrated. In order to determinate the species richness of Glypthelmins in Mexico, from December, 1996 to September, 2002, 33 species of anurans from 50 localities distributed in 13 states of Mexican Republic were collected. A total of 1060 host were studied, and nine species of Glypthelmins and two morphotypes were obtained. Of the 33 species of anurans studied only 13 were parasitized by one or more species of Glypthelmins. The different species of Glypthelmins are distributed in 20 of the 50 studied localities. This study increases the host range and geographic distribution of the genus, because 13 new host records and 25 new locality records were additioned. Three new species are described: Glypthelmins poncedeleoni, parasitizing Leptodactylus melanonotus from Tabasco and Guerrero; G. brownorumae, parasitizing Rana brownorum from Tabasco, and G. tuxtlasensis, parasite of R. vaillanti from Veracruz, Mexico. The last two species were described by using a combination of molecular data from mtDNA (gen cox1), rDNA genes 5.8S y 28S, and ITS2), and morphological characters. To probe if the genus Glypthelmins is a monophyletic group and to define the species composition, a phylogenetic analysis based on the principles of phylogenetic systematics was conducted. A database including 45 morphological characters with 112 characters states was assembled. Database included 35 taxa, 30 of them belonging to the ingroup, and the remaining five were used as outgroups. The phylogenetic analysis using a heuristic search under the maximum parsimony criteria produced one single most parsimonious tree (L= 1587, CI=0.40, RI= 0.76). The results demonstrated that Glypthelmins not conform a monophyletic assemblage, because the tree is constituted by three main groups, two of them conformed by Choledocystus and Rauschiella. Glypthelmins can be defined as a monophyletic group only if it include: G. quieta, G. californiensis, G. parva, G. intestinalis, G. shastai, G. facioi, G. pennsylvaniensis, G. hyloreus, G. brownorumae y G. tuxtlasensis. This species conform a group supported by a metraterm running dorsally to the cirrus sac. In this study, it is proposed the re-establishment the genera Choledocystus and Rauschiella, and it is considered that these are represented by eight and 12 species, respectively. The genus Choledocystus is supported by having a ratio between oral sucker-acetabulum equal or higher to 0.9 times. The species included in Rauschiella share an inequivocal synapomorphy, vitelline follicles are grouped in lateral fields along the body. With the aim of clarifying the systematic position of Glypthelmins within the order Plagiorchiida, partial sequences of the 28S ribosomal gene of 11 species of Glypthelmins were obtained. The fragment of the ribosomal gene 28S for 11 species of Glypthelmins was of 1270 bp. Analyzing the obtained sequences of some species of Glypthelmins along with other sequences of 54 species of digeneans included in Plagiorchiida, we obtained four most parsimonious trees generated through 1000 random taxa addition heuristic searches with Tree Bisection-Reconnection (TBR) branch swapping options, using a heuristic search. All the threes showed that the 11 species of Glypthelmins do not constitute a monophyletic assemblage, since Glypthelmins hepatica, G. tineri, and G. poncedeleoni appear closely related to other genera of digeneans. The results of the molecular analysis agree with those of the morphological analysis. Both analyses demonstrated that G. hepatica belongs to Choledocystus, while G. tineri and G. poncedeleoni are members of Rauschiella. With the information we obtained in this study, we propose that the genera Glypthelmins, Choledocystus and Rauschiella should be considered valid taxonomically. Genera Margeana, Haplometrana and Hylotrema are considered synonyms of Glypthelmins. Additionally, the genus Repandum is synonymy of Rauschiella, and Reynoldstrema is not considered valid. Following the results of the morphological and molecular studies we define that only five species of Glypthelmins are distributed in anurans from Mexico. These species are parasites of members of the “R. pipiens” and “R. palmipes” complex of both the nearctic and neotropical biogeographical regions. The remaining species, anteriorly considered members of Glypthelmins, should be placed in Choledocystus (C. hepatica), and in Rauschiella (R. tineri, R. linguatula and R. poncedeleoni).
    06/2004, Degree: Ph. D., Supervisor: Gerardo Pérez