Flukes

7 Key excerpts on "Flukes"

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  Microbiology

  Principles and Explorations

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

    (Publisher)

  Flukes Two types of fluke infections occur in humans. One involves tissue Flukes, which attach to the bile ducts, lungs, or other tissues; the other involves blood Flukes, which are found in blood in some stages of their life cycle. Tissue Flukes that parasitize humans include the lung fluke, Paragonimus westermani, and the liver Flukes, Clonorchis sine-nsis (Figure 12.17a) and Fasciola hepatica. Blood Flukes include various species of the genus Schistosoma. Parasitic Flukes have a complex life cycle (Figure 12.18), often involving several hosts. The fusion of male and female gametes produces fertilized eggs that become encased in tough shells during their passage through the female fluke’s uterus. The eggs pass from the host with the feces. When the eggs reach water, they hatch into free-swimming forms called miracidia (mi′′ra-sid′e-ah). The miracidia pen- etrate a snail or other molluskan host, become sporocysts, and migrate to the host’s digestive gland. The cells inside the sporocysts typically divide by mitosis to form rediae (re′de-e). Rediae, in turn, give rise to free-swimming 2. Worms mate and lay eggs in hepatic portal vessels 3. Fertilized eggs leave intestinal wall and pass to outside in feces Free-swimming miracidium enters snail (alternate host) and develops into a sporocyst 6. Sporocysts develop into cercaria and are released into water 7. Cercaria enter the body, lose their tails, and encyst as metacercaria 4. Eggs hatch in water 1. Maturation into adult worm occurs 1. Male worm holds female within a cleft in his body Eggs Miracidium Hepatic portal vessels In human Free-swimming cercaria Blood vessel Liver 5. Metacercaria FIGURE 12.18 The life cycle of a blood fluke, Schistosoma japonicum. This organism causes schistosomiasis. Unlike some Flukes, S. japonicum does not have a redia stage, nor does it enter an arthropod host. (Juergen Berger/ Science Source) © John Wiley and Sons, Inc.

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  Echinoderm and Platyhelminthes (Animal Phylum)

  • (Author)
  • 2014(Publication Date)
  • White Word Publications

    (Publisher)

  The skin of all species is a syncitium, a layer of cells that shares a single external membrane. Trematodes are divided into two groups, Digenea and Aspidogastrea (also known as Aspodibothrea). Digenea These are often called Flukes as most have flat rhomboid shapes like that of a flounder (Old English flóc ). They have about 11,000 species, more than all other platyhelminthes combined, and second only to roundworms among parasites on metazoans. Adults usually have two holdfasts, a ring round the mouth and a larger sucker midway along what would be the underside in a free-living flatworm. Although the name Digeneans means two generations, most have very complex lifecycles with up to seven stages, depending on what combinations of environments the early stages encounter – most importantly whether the eggs are deposited on land or in water. The intermediate stages transfer the parasites from one host to another. The definitive host in which adults develop is a land vertebrate, the earliest host of juvenile stages is usually a snail that may live on land or in water, and in many cases a fish or arthropod is the second host. For example, the adjoining illustration shows the life cycle of the intestinal fluke metagonimus, which hatches in the intestine of a snail; moves to a fish where it penetrates the body and encysts in the flesh; then moves to the small intestine of a land animal that eats the fish raw; and then generates eggs that are excreted and ingested by snails, thereby completing the cycle. Schistosomes, which cause the devastating tropical disease bilharzia, belong to this group. Adults range between 0.2 mm (0.0079 in) and 6 mm (0.24 in) in length. Individual adult digeneans are of a single sex, and in some species slender females live in enclosed grooves that run along the bodies of the males, and partially emerge to lay eggs. In all

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  Pests

  A Guide to the World's Most Maligned, Yet Misunderstood Creatures

  • Ross Piper(Author)
  • 2011(Publication Date)
  • Greenwood

    (Publisher)

  Back then the disease was known to infect around 124 million people, so when we consider the current incidence and factor in inflation, the global eco- nomic burden of this disease today must be enormous. LIVER Flukes The schistosomes are widespread parasites of humans, but there are many other digenea that cause disease in humans and livestock alike. Perhaps the most well known of these, and probably the most well known of all endoparasites, are the liver Flukes (Fasciola spp. and Fascioloides spp.), large, flat leaf-shaped organisms, which spend their adult life in the bile ducts of mammals, including humans. The liver Flukes find their way into the mammal definitive host by using an aquatic snail as an intermediate host and then encysting on aquatic vegetation relished by mammals. The liver Flukes are a rare parasite of humans today, although the number of people becoming infected with these parasites has been steadily increasing since 1980. Over a 25-year period from 1973 to 1998, there were 7,071 cases of Fasciola hepatica infection in 51 countries. This is relatively minor compared to their impact on the various herbivorous mammals we have domesticated. In both humans and ungulates, liver Flukes cause disease (fascioliasis) by damaging the liver, bile duct, and gall bladder. Rarely, a liver fluke infection can be fatal, but more often it is just the overall vital- ity of the host that is reduced as an infected animal fails to thrive. In some 220 PLATYHELMINTHES: TREMATODES areas, the incidence of liver fluke infection may be as high as 70 percent, which carries a significant economic burden for livestock farmers attempt- ing to rear healthy animals for meat and milk production.

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  Food Safety

  The Science of Keeping Food Safe

  • Ian C. Shaw(Author)
  • 2018(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Parasites comprise a broad array of different creatures all with one goal, to live for free! They utilise nutrients from another animal (or plant) – the host – and give nothing in return. Parasites in a food safety context have a human host as part of their complex lifecycles and are transmitted in food. They are all destroyed by cooking and so are only a problem in undercooked food (e.g. pork) or food eaten raw (e.g. fish sashimi).

  Food‐borne parasites are categorised as parasites because of their lifestyle (i.e. robbing their food from others) and not based on phylogenetics. For this reason parasites range from simple single‐celled animals (e.g. Giardia) to complex multi‐celled animals (e.g. flatworms).

  Flatworms – Platyhelminthes

  The phylum Platyhelminthes (from the Greek πλατύ (platy) meaning flat; ἕλμινς (helminth) meaning worm) includes four classes; three of them are parasites, namely cestodes (tapeworms), trematodes (Flukes) and monogenea (parasitic flatworms). Only cestodes and trematodes are human parasites.

  Tapeworms – Cestodes

  The tapeworms have complex lifecycles usually involving at least two host species; those important as food‐borne pathogens have humans as one of the hosts. I will discuss several important food‐transmitted tapeworms and describe their lifecycles in a little more detail below.

  The symptoms of tapeworm infection are often hunger and loss of weight. This is because the tapeworm is helping itself to the host's partly digested food as it grows in the host's gut which means that less food is absorbed by the host and so she/he feels hungry and loses weight.

  Anatomy of a tapeworm

  All of the tapeworms have the same basic structure: they have a ‘head’ or scolex with hooks to allow the animal to hold firmly onto the intestine wall of its host, and a long, often very long (up to 5 m), segmented body (Figure 5.1

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  Amphibian Declines

  The Conservation Status of United States Species

  • Michael Lannoo(Author)
  • 2005(Publication Date)
  • University of California Press

    (Publisher)

  7. The life cycle is typically completed when second inter-mediate hosts are eaten by definitive hosts, where metacercariae are excysted and migrate to their final sites within the host to develop as egg-producing adult worms. Adult trematodes are monecious (complete male and fe-male reproductive systems develop in an individual worm). Being members of the phylum Platyhelminthes (“flatworms”), most Flukes are dorsoventrally flattened and oval in shape. The typical adult trematode has two muscular suckers used for at-tachment. An anterior oral sucker surrounds the mouth and a powerful ventral acetabulum is located somewhere behind the oral sucker. The digestive system consists of a mouth, a muscu-lar pharynx used for ingesting food, and a short esophagus that branches into two intestinal cecae. Trematodes do not have an N I N ETE E N Parasites of North American Frogs DANIEL SUTHERLAND 110 PARASITES OF NORTH AMERICAN FROGS Glypthelmins quieta (Fig. 19-1J) occur in the intestine of var-ious ranids. Physid snails are first intermediate hosts for mother and daughter sporocysts. Cercariae encyst in the skin of frogs and enter the frog intestine when bits of epidermis are shed and ingested (Rankin, 1944; Leigh, 1946; Schell, 1962). Other species of Glypthelmins (and the closely related Hy-lotrema ) infect treefrogs (Hylidae) and apparently have life cy-cles where cercariae penetrate to the coelom of tadpoles and become unencysted metacercariae (e.g., Brooks, 1976a). They remain in the coelom until metamorphosis, at which time metacercariae migrate to the adult’s intestine (Schell, 1985). Cephalogonimus also inhabit the intestines of frogs of the genus Rana . Embryonated eggs are ingested by snails ( Helisoma sp). Cercariae then develop in daughter sporocysts in the he-mocoel. After leaving the snails, cercariae penetrate and encyst in tissues of tadpoles. Adult Flukes develop in the intestine when infected tadpoles are eaten (Lang, 1968).

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  Medical Microbiology E-Book

  A Guide to Microbial Infections

  • Michael R. Barer, Will L Irving, Michael R. Barer, Will L Irving(Authors)
  • 2018(Publication Date)
  • Elsevier

    (Publisher)

  Closely related species have occasionally been implicated in human disease in parts of Africa and South America. Human infection follows ingestion of raw, infected muscle of freshwater crabs and crayfish. The metacercariae penetrate through the gut wall and diaphragm to reach the lung, where they develop to maturity. Occasionally the larvae find their way to the brain. Pulmonary infection usually provokes the production of sputum, in which the characteristic large eggs (Fig. 60.4C) can be found, often associated with flecks of altered blood. Praziquantel is used for treatment. Intestinal Flukes Several genera of intestinal Flukes cause human infection, particularly in the Far East. Fasciolopsis buski is found in restricted foci in China and Southeast Asia. Infection is often acquired by the habit of opening water chestnuts with the teeth. The adult Flukes live attached to the wall of the small intestine and produce a large number of eggs that resemble those of F. hepatica. Schistosoma species The schistosomes, or blood Flukes, also known as bilharzia, after the discoverer Theodor Bilharz, are the most important of the pathogenic trematodes. At least 200 million people are infected, principally in Africa, where S. mansoni and S. haematobium are widespread, and S. intercalatum is encountered in some areas. S. mansoni is also found in parts of the West Indies and South America; S. japonicum and the related S. mekongi are restricted to the Far East. Human infection follows exposure to cercariae in water harbouring infected snails. The cercariae penetrate the skin, often causing a transient dermatitis called swimmer's itch. Once in the bloodstream, the schistosomula migrate to the liver, where they develop into adult worms. The integument of the mature male worm is adapted in the form of two long flaps, the gynaecophoral canal, in which the female is held. The mature worms migrate to the small veins of the rectum (S. mansoni, S. intercalatum, S. japonicum and S

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  Parasitology

  An Integrated Approach

  • Alan Gunn, Sarah J. Pitt(Authors)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  5 Platyhelminth and Acanthocephalan Parasites

  CONTENTS

  • 5.1 Introduction
  • 5.2 Phylum Platyhelminthes
  • 5.2.1 Trematoda
  • 5.3 Class Cestoda
  • 5.3.1 Order Pseudophyllidea/Diphyllobothridea
  • 5.3.2 Order Cyclophyllidea
  • 5.4 Phylum Acanthocephala

  5.1 Introduction

  In this chapter, we will introduce three of the most important groups of parasitic ‘worms’. Namely, the flatworms (Flukes), the tapeworms, and the thorny headed worms. The term ‘worm’ is, in a way, unfortunate because these organisms are only very distantly related to the real worms – the Annelida. Furthermore, most Annelida are free‐living although one group, the Hirudinea, includes the leeches, some of which feed on blood and some people consider these to be parasites. The thorny‐headed worms or acanthocephalans to give them their scientific name are unusual parasites. They are common parasites, but they rarely infect humans and domestic animals and therefore seldom gain attention in the scientific literature. They do, however, have some fascinating biological traits.

  5.2 Phylum Platyhelminthes

  Members of the phylum Platyhelminthes are commonly known as the ‘flatworms’ on the not unreasonable basis that they are dorsoventrally flattened and worm‐like in appearance. They are acoelomate soft‐bodied animals that are bilaterally symmetrical (i.e., their left side is the same as their right side) with an obvious head‐end. Most platyhelminths have a mouth at the anterior end although in some free‐living species the mouth is situated at or close to the centre of the body, while in tapeworms the mouth is absent. Tapeworms also lack a gut although this is present in most other platyhelminth species and usually consists of a blind‐ending sack or series of branching tubules. The lack of an anus means that waste material is passed back through the mouth. Platyhelminths do, however, have a ramifying series of tubules that constitute their ‘excretory system’. Flame cells (protonephridia) maintain the movement of fluid within the excretory system, and the waste is removed through excretory pores. Because the excretory system removes excess water and ions, it is sometimes referred to as the osmoregulatory system. Most platyhelminths are hermaphrodites, containing both male and female reproductive organs, although in a few species there are separate male and female sexes.

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