Helminths

10 Key excerpts on "Helminths"

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  eBook - PDF

  Handbook of Helminthiasis for Public Health

  • D. W. T. Crompton, Lorenzo Savioli(Authors)
  • 2006(Publication Date)
  • CRC Press

    (Publisher)

  43 4 Common Themes and Concepts in Helminthiasis Some information about Helminths, the diseases they induce, and approaches to their control have general application to each of the nine groups discussed in this hand-book (Chapter 5 to Chapter 13). Each species of helminth considered here to be an agent of disease lives for part of its development or reproductive life inside the human body. The dynamic relationship between Helminths and their human hosts exemplifies parasitism. Each is a partner of a pair of interacting species that, through evolutionary progression, have acquired integrated genomes so that the parasitic species is dependent on at least one gene or gene product of the host species (MacInnes, 1974). And at some stage in its life history, a parasite is more than likely to obtain nutrients and energy from the food, metabolites, or tissues of its host. 4.1 HISTORY AND DISCOVERY A meticulous account of how our ancestors regarded the Helminths with which they came into contact and how earlier generations of helminthologists set about studying helminth origins, transmission, and life histories has been compiled by Grove (1990). Contributors to a volume edited by Cox (1996) have given accounts of discoveries leading to the recognition of Helminths as agents of disease while Kean et al. (1978) published a volume covering classic investigations into human helminthiasis. Con-temporary health professionals are now able to embark on helminth control thanks to the body of work based on the efforts of the pioneers reviewed in these publications. 4.2 NOMENCLATURE Helminthiasis is the term used to describe the disease that accompanies infection of humans with a species of endoparasitic worm. The suffix “-iasis,” when attached to the name of a worm or group of worms such as ascariasis or cestodiasis, indicates disease due to Ascaris lumbricoides or to a group of cestodes.

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  Immunity to Parasitic Infection

  • Tracey Lamb(Author)
  • 2012(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Section 3 Passage contains an image 10 Introduction to Helminth Infections David B. Guiliano School of Health, Sport and Bioscience, University of East London, London, UK

  The word helminth – or geohelminth – is derived from the Greek ‘helmins’ or ‘helmithos’, translating as ‘worm’; it is an umbrella term commonly used to describe a group of parasitic organisms having ‘worm-like’ anatomical characteristics. Zoologically, ‘helminth’ has come to encompass several large groups of parasitic invertebrates which we now know to be unrelated’ despite sharing some gross morphological features. These groups include the platyHelminths, nematodes, nematomorphs, acanthocephalids, and pentastomids. One of the common hallmarks of these organisms is their complex life cycles, often involving multiple hosts and highly adapted reproductive strategies.

  Helminths have long been recognised as causative agents of disease in humans and other animals and have shaped societal habits in many parts of the world. One example of Helminths shaping societal eating habits is the prohibition against eating pork products in several religious practices. ‘And the swine, though he divide the hoof, and be cloven footed, yet he cheweth not the cud; he is unclean to you’ (Leviticus 11: 7–8). Many believe this prohibition arose because of infections with pork tapeworm (Taeniasis, Taenia solium ; Chapter 17) and Trichinella spiralis (Trichinosis; Chapter 15), which would have been common in domesticated pigs at that time.

  Parasitic worms infect billions of people annually and continue to be important human pathogens. The WHO has calculated that millions of disability-adjusted life years (DALYs) are lost annually due to helminth infections. However, epidemiological studies have shown that, unlike many of the protozoal diseases, most helminth infestations are generally asymptomatic and rarely life-threatening, even in individuals harbouring heavy infections. This bespeaks either a remarkable degree of immunological trickery on the part of the parasite, or apathy by the host. Either possibility makes this a fascinating area of study for immunologists and those trying to develop vaccines to target these pathogens.

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  Yamada's Textbook of Gastroenterology

  • Daniel K. Podolsky, Michael Camilleri, J. Gregory Fitz, Anthony N. Kalloo, Fergus Shanahan, Timothy C. Wang, Daniel K. Podolsky, Michael Camilleri, J. Gregory Fitz, Anthony N. Kalloo, Fergus Shanahan, Timothy C. Wang(Authors)
  • 2015(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  CHAPTER 122 Parasitic Diseases: Helminths Thormika Keo, John Leung, and Joel V. Weinstock Tufts Medical Center, Boston, MA, USA

  Chapter menu

  1. Introduction, 2337
  2. Stool examination for parasites, 2338
  3. Nematodes (roundworms), 2340
  4. Trematodes (flukes), 2357
  5. Cestodes (tapeworms), 2367
  6. Immune-mediated diseases and their relationship to improved hygiene and deworming of the population, 2376
  7. Acknowledgment, 2377
  8. Further reading, 2377

  Introduction

  Helminths are complex animals with worm-like morphology and well developed organs. The word helminth is a derivative of the Greek word helmins, which translates to worm. The various adult species can range in size from several millimeters to many meters long. They display different morphological forms as they pass through various stages of their life cycles. There are species of Helminths adapted to all regions of the world, but many survive best in warmer regions because of peculiarities of their life cycles. On the tree of evolution, the first Helminths date back to at least the time of the dinosaurs [1].

  Globally, Helminths presently colonize perhaps a third of all people. Helminthic colonization was nearly universal before the 20th century [2,3]. Public health departments partially documented the prevalence of worm infections in the United States. In the first half of the 20th century, worm carriage was especially common in the rural South and in poorer inhabitants of major cities [4]. They presently are found occasionally in financially deprived people in underserved regions of the United States [5]. Their prevalence remains high in younger-aged immigrants from less developed countries [6]. The distribution of helminthic infections likely will shift with continued economic and cultural globalization, and climate change.

  Humans are often still exposed to various Helminths of domesticated or wild animals. This results from contact with pets, soil, and hunting, and the practices of animal husbandry and farming. Most of these Helminths cannot sustain human colonization and do not cause human disease (e.g., Trichuris suis). A few animal Helminths, such as Dirofiliaria immitis (dog heartworm), Trichinella spiralis, and Toxocara canis

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  Textbook of Gastroenterology

  • Tadataka Yamada(Author)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  107 Parasitic diseases: Helminths Carlos Seas, Martin Montes, A. Clinton White Jr

  Intestinal nematodes(roundworms) Trematodes (flukes) Cestodes

  Helminth parasites, or worms, are multicellular eukaryotic organisms that are common inhabitants of the human gastrointestinal track. Throughout human history, parasitism with Helminths has been a normal part of the human condition [1–3]. Only with the development of improved standards of sanitation, housing, and food preparation in the 20th century did the prevalence of these infections decrease in wealthy countries. In contrast, the total number of infected individuals continued to increase throughout most of the 20th century. Data from the late 20th century highlighted the previously unrecognized burden of morbidity, focusing on the role of Helminths in chronic malnutrition, anemia, and accompanying cognitive defects, leading to the recognition that intestinal Helminths are neglected tropical diseases of global public health importance [4,5].

  Helminths are multicellular members of the animal kingdom, large enough to be visible to the human eye at some point in their life cycle. Parasites have different morphological forms that vary with the host and environment and most have an obligate one-way life cycle. In contrast to most microorganisms, Helminths do not typically reproduce within the human host. Thus, the parasite burden is largely a reflection of the infecting dose and host control of infection. Interestingly, the population structure of worm burden in communities is typically overdispersed, i.e., most of the worms live in a small portion of the population. Most of this pattern appears related to genetic predisposition [6].

  Helminths are categorized into three major groups: nematodes, trematodes, and cestodes. Nematodes are roundworms with a tubular gut including both a mouth and anus. There are two groups of flatworms: trematodes and cestodes. Trematodes, or flukes, are flat leaf-shaped organisms with a blind gut. All require an obligate freshwater snail host. The cestodes, or tapeworms, typically have two distinct forms. The adult forms a tapeworm in the gut of the definitive host and possesses an attachment organ (scolex) and segments (proglottids). While not having a separate gut, the external surface shares many features with the mammalian digestive tract. The proglottids are hermaphroditic, containing both ovaries and testes. The larval forms develop as cystic lesions in the tissues of the intermediate host. Some species have a second intermediate host. Many parasites use humans as an obligate host in their life cycle. In addition, related animal parasites often infect people and cause human disease. Zoonotic infections are noted with all the major nematodes groups as well as some trematodes and cestodes. The major human intestinal Helminths and their treatment are detailed in Table 107.1

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  Changing Diversity in Changing Environment

  • Oscar Grillo, Gianfranco Venora, Oscar Grillo, Gianfranco Venora(Authors)
  • 2011(Publication Date)
  • IntechOpen

    (Publisher)

  According with Hugot et al. (2001) the term ‘helminth‘ was originally used for worms living in the digestive tract of humans and animals, and thus was allied with the general concept of parasitism. Parasitism as a way of life evolved from free-living counterparts several times during the evolutionary history of life on earth. Helminths, as parasites in general, do not represent a monophyletic assemblage since under that term, members of phylogenetically not related phyla are included, i.e., Platyhelminthes (flatworms), Nematoda (roundworms), Acanthocephala (thorny-headed worms), and Hirudinea (leeches) (Fig. 1). Members of these groups are characterized as macroparasitic metazoans with a vermiform appearance, even though they represent independent evolutionary lineages. Some species have medical importance, e.g., Taenia solium and Ascaris lumbricoides , the first one causing diseases referred as teniosis (and cisticercosis when the larval form is the causal agent), and the second one causing ascariosis. Most helminth species possess a complex life cycle that involves one or more intermediate host, although some exhibit a direct life cycle (e.g., monogeneans). PlatyHelminths are characterized as dorsoventrally flattened acelomates with bilateral symmetry, and most of them are hermaphrodites. Among flatworms, free-living species are found, however, parasitic platyHelminths are included in three major groups, digeneans, monogeneans, and cestodes (Fig. 1) (Roberts & Janovy, 2005). Nematodes also contain free-living and parasite species; these are pseudocoelomate roundworms, with sexual dimorphism. The entire phylum Acanthocephala is represented by parasite species that infect, as adults, the digestive tract of vertebrates. Acanthocephalans are also pseudocoelomate worms diagnosed by possessing a particular attachment organ (proboscis) armed with hooks.

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  Microbiology

  Principles and Explorations

  • Jacquelyn G. Black, Laura J. Black(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  Unless health scien- tists take a course in parasitology, their only opportunity to learn about Helminths and arthropods is in conjunction with the study of microscopic infectious agents. PRINCIPLES OF PARASITOLOGY A parasite is an organism that lives at the expense of another organism, called the host. Parasites vary in the degree of damage they inflict on their hosts. Although some cause little harm, others cause moderate to severe damage. Parasites that cause disease are called pathogens. Parasitology is the study of parasites. Although few people realize it, among all living forms, there are probably more parasitic than nonparasitic organisms. Many of these parasites are microscopic throughout their life cycle or at some stage of it. Historically, in the development of the science of biology, parasitology came to refer to the study of protozoa, hel- minths, and arthropods that live at the expense of other organisms. We will use the term parasite to refer to these organisms. Strictly speaking, bacteria and viruses that live at the expense of their hosts also are parasites. The manner in which parasites affect their hosts dif- fers in some respects from that described in earlier chap- ters for bacteria and viruses. Special terms also are used to describe parasites and their effects. This introduction PRINCIPLES OF PARASITOLOGY 298 The Significance of Parasitism 298 • Parasites in Relation to Their Hosts 298 • Wolbachia 299 PROTISTS 300 Characteristics of Protists 300 • The Importance of Protists 300 • Classification of Protists 301 FUNGI 307 Characteristics of Fungi 307 • The Importance of Fungi 310 • Classification of Fungi 311 CHAPTER MAP Helminths 315 Characteristics of Helminths 315 • Parasitic Helminths 316 ARTHROPODS 323 Characteristics of Arthropods 323 • Classification of Arthropods 323 to parasitology will make discussions of parasites here and in later chapters more meaningful.

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  Applied and Economic Zoology

  • Rathoure, Ashok Kumar(Authors)
  • 2021(Publication Date)
  • Daya Publishing House

    (Publisher)

  Pinworms, hookwormsand roundworms are extremely common intestinal helminth infections of humans; worldwide, roundworms are probably the most common. Pinworm transmittal generally occurs through ingestion of fecal contaminated material and infection occurs commonly in children. Other helminth infections are vectored as filarial worms by insects such as mosquitosor the filaria may penetrate directly through the skin from water or soil. Filarial worms cause such diseases as river blindness ( Onchocerca volvulus ) and elephantiasis which are major health problems in some third world countries. Most helminth infections of This ebook is exclusively for this university only. Cannot be resold/distributed. humans can be controlled by public health programmes, public education, vector control, intermediate host control and anthelminthic drugs. Helminth Parasites The word helminth is a general term meaning worm, but there are many different types of worms. Prefixes are therefore used to designate types such as platyHelminths for flat-worms and nematoHelminths for round-worms. All Helminths are multicellular eukaryotic invertebrates with tube like or flattened bodies exhibiting bilateral symmetry. They are triploblastic (with endo, meso and ecto-dermal tissues) but the flatworms are acoelomate (do not have body cavities) while the roundworms are pseudocoelomate with body cavities not enclosed by mesoderm. In contrast, segmented annelids such as earthworms are coelomate with body cavities enclosed by mesoderm. Many Helminths are free living organisms in aquatic and terrestrial environments whereas others occur as parasites in most animals and some plants. Parasitic Helminths are an almost universal feature of vertebrate animals; most species have worms in them somewhere. Three major assemblages of parasitic Helminths are recognized; Nemathelminthes (nematodes) and Platyhelminthes (flatworms), the latter being subdivided into Cestoda (tapeworms) and the Trematoda (flukes).

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  Biodiversity

  Threats and Conservation

  • R C Sobti(Author)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  Parker, 2014 ).

  26.2 Helminths and Autoimmune Diseases

  The autoimmune diseases are one of the leading causes of death in women less than 65 years of age. The increase in the rate of emergence of these diseases during past few decades indicates that there might be some environmental factors also that might be contributing to the immune dysfunction leading to autoimmunity problems, allergies, and numerous other inflammatory diseases (Elliott and Weinstock, 2012 ). Many of the experts in the scientific community believe that although many striking environmental changes that have occurred since industrialization began in the 20th century, one that stands out is the loss of exposure to parasitic worms, especially the Helminths. Human beings and Helminths share a very close association that dates back to the era of our earliest recorded history, and the evidence of this association has been established through the recovery of eggs of intestinal Helminths from the mummies, coprolites, and skeletons, dating back to thousands of years (Camacho et al., 2018 ). Also, there is a written evidence about helminth infections from the ancient literature of Hippocrates, Egyptian medical papyri, and the Bible (Hotez et al., 2008 ). Breaking this long-standing relationship between the helminth and humans could have immediate effects on our immune system. Following adaption to the micro-environment within their definitive host, the helminth parasites establish a successful host-parasite relationship by overcoming the host-mounted rejection responses. Helminths are known to synthesize and excrete/secrete a number of immunomodulatory molecules that help in their successful establishment by altering both the innate and adaptive immune responses (Ryan et al., 2020 ). Some of the immunomodulatory molecules derived from the liver flukes, Fasciola spp., are summarized in Figure 26.1

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  Medicine and Evolution

  Current Applications, Future Prospects

  • Sarah Elton, Paul O'Higgins, Sarah Elton, Paul O'Higgins(Authors)
  • 2008(Publication Date)
  • CRC Press

    (Publisher)

  106,107 Again, if our conjectures are correct, another tragic side effect of helmin-thic infection in hominins is that the worms that we harbor today have been with us for thousands if not millions of years. This does not mean that main-taining large worm burdens is not costly to hosts, but rather that the majority of humans have lost, and continue to lose, this host-pathogen arms race. It would be interesting to come up with an approximate number for the total volume of the helminth biomass that humans harbor in their intestines in the world today, to divide that number by the total volume of the biomass of human hosts, and then to do the same calculation for indigenous versus nonindigenous rural and urban groups in developed and underdeveloped countries. This would give us a better appreciation for the energy that hel-minthes are extracting from humans on a macroscale. The evolutionary implications of this helminth-centered view of human biology in the twenty-first century are considerable. How much of the energy that humans now invest directly or indirectly in defense against helminthes could be diverted into other fitness- and health-enhancing physiological functions across the life course if helminthes could be eradicated from the planet? How would that affect global health patterns? In addition to the more obvious effects, such as healthier overall developmental trajectories for children, and a longer, healthier life span, the impact of helminth eradica-tion on the rates of emergence of new viral and bacterial infections, and the rates of transmission of their older counterparts, could be significant. If in fact helminthes make hosts more susceptible to pathogenic viruses and bac-teria through mechanisms that downregulate the cells involved in the Th1 response, then, on a global scale, eradication of helminthes would in effect lead to a reduction of the number of susceptibles to new and old viral and bacterial infections.

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  Ecology and Physiology of Parasites

  A Symposium

  • A. Murray Fallis(Author)
  • 2019(Publication Date)
  • University of Toronto Press

    (Publisher)

  Helminths as vectors of micro-organisms D. L. LEE It is common knowledge that arthropods are important vectors of micro-organisms and as such are responsible for disseminating many di-seases of man, other animals, and plants. Few people seem to realize, however, that some para-sitic worms are also important as vectors of micro-organisms. This interesting aspect of the host-parasite relationship and of parasite ecology is one that is comparatively neglected. The Helminths which have been implicated in the transmission of micro-organisms are the nematodes, the trematodes, and the cestodes, the most important of these being the nematodes. (By micro-organisms I mean viruses, rickettsia, bacteria, and protozoa.) The literature up to 1960 on Helminths as vec-tors of micro-organisms was reviewed in two papers in a symposium on the biological trans-mission of disease agents held by the Entomolo-gical Society of America. One paper by Hewitt and Raski (1962) was on nematode vectors of plant viruses and concentrated on the transmis-sion of grape-vine fan-leaf virus by the plant-parasitic nematode Xiphinema index, and the other, by Philip (1962), was on Helminths as carriers of microbial disease agents of man and animals. Here I shall review only the more thoroughly established examples in the literature up to 1960, leaving the reader to look up the more speculative relationships between hel-minths and microbial agents in these earlier re-views. Since digenetic trematodes and cestodes usu-ally have complex life cycles involving one or more intermediate hosts, they should, theoretic-ally, be unsuitable as vectors of micro-organisms. There is, however, one well-documented ex-ample of a trematode, and a less well documented one of a cestode, acting as a vector. Helminths AS VECTORS OF MICRO-ORGANISMS 105 TREMATODES Nanophyetus salmonicola is a digenetic trema-tode, less than 1 mm in length, which lives in the small intestine of fish-eating mammals, including the dog.

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