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Parasitology 101 for Environmental Health

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Parasitology 101 for Environmental Health – PowerPoint PPT presentation

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Title: Parasitology 101 for Environmental Health


1
Parasitology 101 for Environmental Health
2
Key Concepts
  • Parasitism Literally to feed at the table of
    another (from the Greek parasitos)
  • Parasite -- A species that is metabolically
    dependent on another species
  • Life cycles -- The key to eradication of
    parasites in an environment

3
Key Definitions
  • Endoparasite -- Resides within the host, e.g.,
    Angiostrongylus
  • Ectoparasite -- Resides outside the host, i.e.,
    on the exterior, e.g., Larva migrans
  • Aberrant parasite - The right host but the wrong
    tissue, e.g., S. haematobium in the eyes
  • Incidental parasite - Wrong host, wrong
    everything.

4
More Terms
  • Facultative parasite - A parasite that can
    exist in a parasitic relationship as easily as
    free-living
  • Obligatory parasiteParasitism is
    necessaryobligatoryfor the parasite to
    survive
  • Pseudoparasite -- Literally a false parasite
    (pseudo)
  • Hyperparasite -- A parasite that parasitizes
    another parasite

5
Types of Hosts
  • Definitive host -- Host on/in which parasite
    reaches sexual maturity
  • Intermediate host -- Host on/in which parasite
    develops sexually but to full maturation
  • Paratenic (transport) host -- Host that moves
    parasite from one host or site to another

6
More Hosts
  • Biologic (Vector) -- Living (usually
    invertebrate) host (e.g., mosquitoes)
  • Mechanical (Vehicle) Non-living host (e.g.,
    water)
  • Reservoir host -- A host that maintains parasite
    in environment (e.g., mammals and Giardia
    lambliae)

7
Basic Varieties of Life Cycles
  • Direct -- Literally direct transmission, e.g.,
    fecal-oral, i.e., Enterobius vermicularis
    (pinworm)
  • Indirect -- Several hosts that maintain sexual
    development (e.g., Angiostrongylus)

8
Basic Types of Transmission
  • Horizontal Indirect in which one host eats
    another host
  • Vertical -- Direct in which mother may pass
    parasite to foetus
  • NB Host specificity If pathogen can jump from
    non-humans to humans, then pathogen is generally
    considered zoönotic.

9
Characteristics of Parasitism of Domestic
Animals
  • Parasitism is extremely common in domestic
    animals
  • Parasitic disease is often relatively rare,
    however, and usually is a consequence of
    management.

10
Characteristics
  • Parasitiasis parasitism (infection), but in the
    absence of the disease
  • Parasitosis parasitism (infection) with the
    presence of the disease

11
Characteristics
  • Parasitic disease is usually related to the
    numbers of parasites present or relative
    susceptibility of the host.
  • Parasites damage hosts by a variety of
    pathophysiologic mechanisms the spectrum of
    damage ranges from no effect to death.
  • Parasitized animals eventually develop some
    degree of acquired immunity to most parasitic
    infections or at least to associated disease.

12
Characteristics
  • The ultimate goal of parasite control is
    disruption of transmission (i.e., prevention of
    infection/reinfection).
  • Disruption of parasitic transmission is rarely
    done by treatment with parasiticides alone.
  • Development of effective host immunity, changes
    in clinical management, and/or modifications of
    the environment are usually necessary to achieve
    effective control.

13
Characteristics
  • The ultimate goal of a parasites existence is
    perpetuation of the species. Many parasites can
    alter their biologic functions to enhance the
    odds for survival and reproduction.
  • Parasite populations are plastic and dynamic
    they have the capacity to respond to a variety of
    conditions and stimuli (selection pressures) by
    alterations of their genetic composition.

14
Parasites May Injure Their Hosts in a Variety of
Ways
15
Injury Risk
  • They may suck blood (mosquitoes, hookworms),
    lymph (midges), or exudates (lungworms).
  • They may feed on solid tissues, either directly
    (giant kidney worms, liver t flukes) or after
    first liquefying them (chiggers, amoebas).
  • They may compete with the host for food it has
    ingested, either by ingesting intestinal contents
    (ascarids) or absorbing them through body wall
    (tapeworms).

16
Injury
  • They may cause mechanical obstructions of the
    intestine (Ascaris spp.), bile ducts (Ascaris
    spp.), blood vessels (Dirophilaria immitis),
    lymph channels (Wuncheria bancrofti), bronchi
    (Strongyloides stercoralis), or other body
    channels.
  • They may cause pressure atrophy (Hydatid cysts
    from Fasciola hepatica).

17
Injury
  • They may destroy host cells by growing in them
    (Plasmodium spp.).
  • They may produce various toxic substances such as
    hemolysins, histolysins, and anticoagulants,
    exudate from biting arthropods.

18
Injury
  • They may cause allergic reactions.
  • They may cause various host reactions such as
    inflammation, hypertrophy, hyperplasia. and
    nodule formation.
  • They may stimulate the development of cancer
    (Schistosoma haematobiuim)

19
Injury
  • They may carry diseases and parasites, including
    malaria (mosquitoes), swine influenza
    (lungworms), salmon poisoning (flukes), and
    heartworms (mosquitoes).
  • They may reduce their hosts resistance to other
    diseases and parasites, thereby setting the host
    from a premature death from something other than
    a parasitic disease.
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