Parasitism

9 Key excerpts on "Parasitism"

• 

  eBook - ePub

  Infection, Resistance, and Immunity, Second Edition

  • Julius Kreier(Author)
  • 2022(Publication Date)
  • Routledge

    (Publisher)

  parasitosis is sometimes used to designate a parasitic relationship that is particularly harmful to the host.

  Figure 2.2. Symbiotic relationships may vary over time. Depending on environmental factors such as host resistance, the relationship of a given host-parasite pair may shift between mutually beneficial (mutualism) and harmful to the host (parasitosis). Intermediate stages of toleration (commensalism) may occur.

  In practice the categories into which host-parasite relationships have been divided are somewhat arbitrary and grade one into the other. This is as one should expect, as host-parasite relationships are subject to and are the results of evolution, and at any given time transformation from one relationship to another may not be complete. Evolution toward mutual interdependence between host and parasite has been realized to a remarkable degree in some instances. As a result of evolutionary change, for example, some mutualistic relationships have become so intimate that the members of the pair are no longer considered separate individuals. This is the case with chloroplasts and the plant cells in which they occur, and with the mitochondria inhabiting plant and animal cells.

  Parasites may be distinguished from predators and from saprophytes. Predators are organisms that hunt, catch, and kill other organisms before eating them. Usually prey and predator are similar in size. The prey may be somewhat smaller than the predator, as is a mouse preyed on by a cat, or larger, as is a deer preyed on by wolves. Parasites, on the other hand, are almost always much smaller than their hosts. Fleas, for example, are much smaller than dogs, and the pneumococcus is much smaller than the human in which it causes pneumonia. The major difference between parasites and predators is not size, however, but behavior. Parasites such as fleas and bacteria do not hunt, catch, and kill their prey before eating it; rather they eat it while it continues to live.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Parasitology

  • Jack Chernin(Author)
  • 2000(Publication Date)
  • CRC Press

    (Publisher)

  IN TR O D U C TIO N TO P A R A S I T O L O G Y ■ 1.1 PARASITES AND Parasitism The w ord ‘parasite’ is derived from the G reek w ords para (m eaning beside) and sitos (m eaning food). Parasites can be described as living organisms that are associated w ith food for all or part of their life-cycle. The organism providing the food is generally called the host. A parasite has at least one host per life-cycle. If there is m ore than one host per life-cycle, the host in which sexual m aturity occurs is referred to as the definitive host and the other h o st/s are know n as interm ediate hosts. The study of parasites invariably involves firstly the biology of the parasite and secondly the biology of the host — the parasite’s environm ent. H ence the following com m ents can be made regarding parasitology: ■ Parasitology can be considered to be a specialised branch of ecology. ■ Parasitology is the study of organisms living w ithin a specialised environm ent. The problem s related to survival for parasites are alm ost the opposite of those faced by free-living animals. Parasites are surrounded by (they live w ithin or on) their food and do not need to spend energy to find food; w hereas free living animals are continuously searching for food. Free living animals have few er problem s than parasites in reproduc-tion and distribution. D uring the distributive phase of its life-cycle, the probability of a parasite making contact w ith a new host is relatively low . The evolution of successful m ethods of invasion and escape is essential for the survival of a parasite. Parasites have evolved mechanism s to ensure distribution and making contact w ith a new host. Similar adaptive strategies that follow a basic ‘parasitic’ plan/design have evolved w ithin different taxonom ic groups.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  The Biology of Parasites

  • Richard Lucius, Brigitte Loos-Frank, Richard P. Lane, Robert Poulin, Craig Roberts, Richard K. Grencis, Ron Shankland, Renate FitzRoy, Ron Shankland, Renate FitzRoy(Authors)
  • 2017(Publication Date)
  • Wiley-VCH

    (Publisher)

  Interactions between individuals of the same species are thus excluded, even if the benefits of such interactions are very often unequally distributed in the colonies of social insects and naked mole rats, for instance, or in human societies. As a result, the interaction between parents and their offspring does not fall under this category, although the direct or indirect manner in which the offspring feed from their parent organism can at times be reminiscent of Parasitism. The principle of one side (the parasite) taking advantage of the other (the host) applies to viruses, all pathogenic microorganisms, and multicellular parasites alike. This is why we often find that no clear distinction is made between prokaryotic and eukaryotic parasites. With regard to parasites, we usually do not differentiate between viruses, bacteria, and fungi on the one hand and animal parasites on the other; we tend to see only the common parasitic lifestyle. Even molecules to which a function in the organism cannot be assigned are sometimes described as parasitic, such as prions, for example, the causative agent of spongiform encephalopathy, or apparently functionless “selfish” DNA plasmids that are present in the genome of many plants. Many biologists are of the opinion that only parasitic protozoa, parasitic worms (helminths), and parasitic arthropods are parasites in the strict sense of the term. Parasitology, as a field, is concerned only with those groups, while viruses, bacteria, fungi, and parasitic plants are dealt with by other disciplines. This restriction clearly hampers cooperation with other disciplines, something that seems antiquated in today's modern biology, where all of life's processes are traced back to DNA; it is gratifying that the boundaries have relaxed in recent years. However, eukaryotic parasites are distinguished from viruses and bacteria by their comparatively higher complexity, which implies slower reproduction and less genetic flexibility

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Interaction and Coevolution

  • John N. Thompson(Author)
  • 2014(Publication Date)
  • University of Chicago Press

    (Publisher)

  A parasite is an organism that lives throughout a major period of its life in or on a single host individual, deriving its food from the host and causing lowered survival or reproduction in the host. Although the term parasite is used most often with reference to small animals or microorganisms that live in or on larger animals—as suggested by the usual content of parasitology journals and texts—this way of obtaining food is common among many taxa. Parasites include, for example, parasitic fungi of plants, herbivores such as caterpillars and aphids that spend all of their larval or nymphal stages on a single host plant, insect parasitoids of other insects that live as larval parasites in their hosts but have a free living adult stage, as well as the parasites usually considered in parasitology such as the cestode parasites of animals. Including the interactions between some phytophagous insects and plants in the application of the term parasite does not broaden the use of the term beyond utility, as has been suggested by some authors (Holling, 1980; Brooks, 1981). Instead, it does just the opposite by using the term in an ecological and evolutionary sense rather than in a sense set arbitrarily by taxonomic boundaries. The purpose of the broad application of the term parasite is to search for general principles that transcend taxonomy in the interactions between organisms (Price, 1975b; 1977; 1980).

  The lack of an absolute discrete boundary between Parasitism and other kinds of interactions between victims and their enemies is at once both exciting to the evolutionary ecologist interested in the evolution of interactions between species and the transition states between, for example, Parasitism and predation, and also frustrating for those interested in categorizing in stone how species interact. Wheeler (1911) notes that “Parasitism is an extremely protean phenomenon, one which escapes through the meshes of any net of scholastic definitions in which we may endeavor to confine it.” Using a definition essentially the same as the one given above, however, Price (1977) estimates that over 50% of extant species are parasitic.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Regulation of Parasite Populations

  • Gerald Esch(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Parasitism and r- and K-selection GERALD W. ESCH, TERRY C. HAZEN AND JOHN M. AHO Department of Biology Wake Forest University Winston-Salem 3 North Carolina U.S.A. and Savannah River Ecology Laboratory Aiken> South Carolina U.S.A. INTRODUCTION The relationship between an organism and its en-vironment can be studied in a number of ways. But for the most part, since suggested by Elton in 1927, the essence of ecology has been the examination of the dis-tribution and abundance of plants and animals in nature. Such an approach can be made at the individual, popu-lation and ecosystem levels of biological organization. While the accent in parasitology has largely been at the individual level and, hence, an emphasis on phys-iology and immunology, in recent times there has been an increasing interest in studying Parasitism at the popu-lation and ecosystem levels. Andrewartha (1970) has said that the aim of population ecology is to explain the numbers of plants or animals which can be counted or estimated in natural populations. In seeking an ex-planation for the numbers of individual organisms, para-9 10 GERALD W. ESCH et al. sitic or otherwise, there are at least two problems which must be resolved. First, the numbers of organ-isms which may be present at a given point in time must be counted, or estimated, accurately. And second, the fundamental nature of change in numbers should be per-ceived, analyzed and related, if possible, to biotic and abiotic variables. In other words, changes in den-sity in a temporal sense must be ascertained and then, an effort must be made to identify the factors which regulate or control the density changes. Obviously, there are a number of highly complex, contributing variables, but in many instances, these have been more than adequately defined and the result has been the formulation of meaningful interpretations, applicable to the regulation of population dynamics.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Rats, Lice and History

  • Allen Grimshaw, Allen Grimshaw, Hans Zinsser(Authors)
  • 2017(Publication Date)
  • Routledge

    (Publisher)

  Parasitism originated in dim primordial antiquity as a consequence of habitual contacts between different living things. It did not develop suddenly, but evolved gradually, as one form adapted itself, step by step, to the environmental conditions found in or upon another. Parasitism, in its origin, means a breaking down of that opposition which, normally, every living cell complex offers to invasion by another living entity. The simplest illustration of this (for want of a better name, we may call it "vital resistance") is the well-known one of the frogs' eggs. They develop and remain free from invasion in a pond which is swarming with bacteria and Protozoa. A frost kills them overnight, and within a few hours their substances have become culture media for innumerable microörganisms. It is conceivable — and, indeed, could be supported by experimental evidence — that a diminution of this "vital resistance" — which is, in itself, a complex phenomenon — may let down the bars sufficiently to permit invaders to gain a preliminary foothold, even though the host does not succumb to the injury which rendered him susceptible. And once begun, the further evolution of Parasitism can proceed in an almost unlimited variety of directions.

  Parasitism represents that phase of evolutionary change which lends itself most easily to analysis. There are few parasites which cannot be traced with considerable clearness to some free-living ancestral stock, either still existent or available in fossil form. From this point of view, the study of parasitic adaptation is one of the most important buttresses of evolutionary theory. Each instance represents a miniature system in which the host is the world by which the parasite is moulded. The Parasitism which is infectious disease involves the invasion of more or less complex plants or animals by simpler, in most cases, unicellular, beings — like the bacteria, the Protozoa, the Rickettsiæ, and the curious, still undefinable agents of which we speak as "ultramicroscopic" or "filterable" viruses. Though actually complex in function and metabolism, these supposedly simple things display an amazing biologic and chemical flexibility; and since, in them, generations succeed each other with great speed (at least two every hour, under suitable circumstances), the phenomena of infection constitute an accelerated evolution extraordinarily favorable for the observation of adaptive changes. It would be surprising, therefore, if new forms of Parasitism — that is, infection — did not constantly arise, and if, among existing forms, modifications in the mutual adjustment of parasites and hosts had not taken place within the centuries of which we have record.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Ecology

  From Individuals to Ecosystems

  • Michael Begon, Colin R. Townsend, John L. Harper(Authors)
  • 2009(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  When the effects of parasites on domesticated animals and crops are added to this, the cost in terms of human misery and economic loss becomes immense. Of course, humans make things easy for the parasites by living in dense and aggregated populations and forcing their domesticated animals and crops to do the same. One of the key questions we will address in this chapter is: ‘to what extent are animals and plant populations in general affected by Parasitism and disease?’ Parasites are also important numerically. An organism in a nat- ural environment that does not harbor several species of parasite is a rarity. Moreover, many parasites and pathogens are host-specific or at least have a limited range of hosts. Thus, the conclusion seems unavoidable that more than 50% of the species on the earth, and many more than 50% of individuals, are parasites. 12.2 The diversity of parasites The language and jargon used by plant pathologists and animal parasitologists are often very different, and there are important differences in the ways in which animals and plants serve as habitats for parasites, and in the way they respond to infection. But for the ecologist, the differences are less striking than the resemblances, and we therefore deal with the two together. One distinction that is useful, though, is that between microparasites and macroparasites (Figure 12.1) (May & Anderson, 1979). Microparasites are small and often intracellular, and they multiply directly within their host where they are often extremely numerous. Hence, it is gen- erally difficult, and usually inappropriate, to estimate precisely the number of microparasites in a host. The number of infected hosts, rather than the number of parasites, is the parameter usually studied. For example, a study of a measles epidemic will involve counting the number of cases of the disease, rather than the number of particles of the measles virus.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Plant Disease Management

  Principles and Practices

  • Hriday Chaube(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Chapter 4Host-Parasite Interaction

  I. Introduction

  Plants are constantly exposed to millions of microorganisms and many of them possess the faculty to attack plants. However, in nature disease is more an exception than a rule. Most of the microbes surrounding the plant are saprophytic, incapable of attacking a healthy plant. Only a few are pathogenic, but each one of these can only attack specific plant species. Furthermore, all the individuals of a host species are not equally susceptible to a given pathogen isolate. How are most of the microbes in contact with the plant surface rendered harmless? How does a plant defend itself against non-pathogens (pathogens of other species) and a pathogen? In order to properly understand these phenomenon it is essential to first understand the nature and evolution of Parasitism in plant pathogens and philosophy of defense in plants.

  II. Evolution of Parasitism

  Unlike their animal counterparts, plants cannot eliminate their parasites; they try to live with them by limiting the latter's deleterious effects. At the same time a successful parasite also can cause less strain to the plant. It is from these considerations that symbiosis is considered to be the most advanced form of Parasitism. In the hypothetical hierarchy (Figure 1 ) of Parasitism it is natural to consider the saprotrophs as the bottom members—they colonize only dead organic matter. The intense competition among the saprotrophs for the same source of organic matter forced some of them to develop parasitic abilities, for example Phytium sp. appears to have the tendencies of a true saprophyte, but it has developed the faculty to become a parasite even though restricted to only attacking the juvenile and succulent plant tissues. Pathogens such as Rhizoctonia sp. and Sclerotium sp. can be considered as more hardy because, in addition to attacking tender tissues, they can also exploit comparatively mature tissues. All these pathogens have a very wide host range. They are necrotrophs, they cause extensive damage to the host tissue by employing enzymes and secondary toxic metabolites as their major weapons. On moving up the hypothetical hierarchical ladder of Parasitism (Figure 1

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Natural Law in the Spiritual World

  • (Author)
  • 2009(Publication Date)
  • The Floating Press

    (Publisher)

  Parasitism * And so I live, you see, Go through the world, try, prove, reject, Prefer, still struggling to effect My warfare; happy that I can Be crossed and thwarted as a man, Not left in God's contempt apart, With ghastly smooth life, dead at heart, Tame in earth's paddock as her prize. ... Thank God, no paradise stands barred To entry, and I find it hard To be a Christian, as I said.— Browning. Work out your own salvation.— Paul. Be no longer a chaos, but a World, or even Worldkin. Produce! Produce! Were it but the pitifullest infinitesimal fraction of a Product, produce it, in God's name!— 329 Carlyle. From a study of the habits and organization of the family of Hermit-crabs we have already gained some insight into the nature and effects of Parasitism. But the Hermit-crab, be it remembered, is in no real sense a parasite. And before we can apply the general principle further we must address ourselves briefly to the examination of a true case of Parasitism. We have not far to seek. Within the body of the Hermit-crab a minute organism may frequently be discovered resembling, when magnified, a miniature kidney-bean. A bunch of root-like processes hangs from one side, and the extremities of these are seen to ramify in delicate films through the living tissues of the crab. This simple organism is known to the naturalist as a Sacculina; and though a full-grown animal, it consists of no more parts than those just named. Not a trace of structure is to be detected within this rude and all but inanimate frame; it possesses neither legs, nor eyes, nor mouth, nor throat, nor stomach, nor any other organs, external or internal. This Sacculina is a typical parasite. By means of its twining and theftuous roots it imbibes automatically its nourishment ready-prepared from the body of the crab. It boards indeed entirely at the expense of its host, who supplies it liberally with food and shelter and everything 330

  Sign up to read

  Learn more about book