Parasite Pathogenicity and Factors

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Questions and Answers

Which factors are important for parasite pathogenicity?

  • Infecting dose and duration of infection (correct)
  • Environmental conditions and host age
  • Virulence factors and host immune response
  • Number of organisms acquired over time and infection route (correct)

What is one common mode of entry for many parasites into the human host?

  • Transplacental penetration (correct)
  • Water absorption
  • Ingestion (correct)
  • Air inhalation

Which of the following parasitic infections can last for months to years?

  • Viral infections
  • Fungal infections
  • Bacterial infections
  • Parasitic infections (correct)

How do many parasites actively invade the human host?

<p>By self-directed means (A)</p> Signup and view all the answers

Which organism is primarily transmitted through direct skin penetration?

<p>Strongyloides stercoralis (B)</p> Signup and view all the answers

Which of the following is NOT a common mechanism of parasitic disease pathogenesis?

<p>Replication within host cells (D)</p> Signup and view all the answers

What route is primarily used for the transmission of Schistosoma haematobium cercariae?

<p>Skin penetration (A)</p> Signup and view all the answers

Which protozoan is mainly transmitted through sexual contact?

<p>Trichomonas vaginalis (C)</p> Signup and view all the answers

What is the initial step in the establishment of a parasitic infection?

<p>Attachment to host tissue (A)</p> Signup and view all the answers

Which statement accurately describes the replication process of protozoan parasites?

<p>Protozoan parasites can replicate intra or extracellularly. (A)</p> Signup and view all the answers

Which mechanism is primarily responsible for damage caused by helminthic parasites?

<p>Mechanical blockage of internal organs (B)</p> Signup and view all the answers

Which pathogenic feature is associated with the parasite E.histolytica?

<p>It produces proteinases that degrade epithelial layers. (A)</p> Signup and view all the answers

What is a common immunologic response to parasitic infections?

<p>Increase in tissue damage due to immune activation (D)</p> Signup and view all the answers

What is a primary factor that determines where a parasite can survive in a host?

<p>Species and tissue tropisms (B)</p> Signup and view all the answers

How do helminths contribute to conditions like elephantiasis?

<p>Through the mechanical pressure they exert in tissues (B)</p> Signup and view all the answers

What mechanism is not involved in establishing a parasitic disease?

<p>Molecular mimicry (A)</p> Signup and view all the answers

What is a distinction between the pathogenic mechanisms of protozoan and helminthic parasites?

<p>Helminthic parasites primarily cause damage through size and movement. (C)</p> Signup and view all the answers

Which organism's infection has been linked to carcinomatous changes in the bile ducts?

<p>Opisthorchis sinensis (C)</p> Signup and view all the answers

Which of the following describes a potential consequence of chronic inflammation due to parasites?

<p>Induction of carcinomatous changes (A)</p> Signup and view all the answers

What is a common characteristic of helminthic infections?

<p>IgE mediated hypersensitivity reactions (A)</p> Signup and view all the answers

Which of the following methods do parasites use to evade host defenses?

<p>Antigenic variation (B)</p> Signup and view all the answers

What type of immunopathologic reaction is associated with Schistosoma infections?

<p>Cytotoxic responses (B)</p> Signup and view all the answers

How do parasites typically cause tissue damage?

<p>Mechanical tissue damage and toxic products (A)</p> Signup and view all the answers

Which route is NOT typically associated with Schistosoma species infections?

<p>Foodborne transmission (C)</p> Signup and view all the answers

Flashcards

Parasite Pathogenicity

Factors determining the severity of a parasitic infection, often related to the infecting dose and duration of infection.

Parasite Entry Modes

Various ways parasites enter the human body, including ingestion, direct penetration, arthropod bites, and transplacental transmission.

Ingestion (Parasite Entry)

Parasites entering the body through consumption of contaminated food or water.

Direct Penetration (Parasite Entry)

Parasites entering the body by directly penetrating the skin or other tissues.

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Arthropod Bite (Parasite Entry)

Parasites transmitted through the bite of an insect vector.

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Transplacental Transmission (Parasite Entry)

Parasites crossing the placenta to infect a developing fetus.

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Protozoan Infection Transmission (Sexual Contact)

Some protozoan parasites, like Trichomonas vaginalis, are spread through sexual contact.

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Parasite Inoculum

The dose or quantity of parasites. Factors like the number/type of parasites and transmission vector are important considerations.

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Tissue Damage (Parasites)

Parasites can harm tissues directly through their migration, toxic products, or mechanical damage.

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Hypersensitivity Reactions (Parasites)

Parasite presence can trigger immune responses that harm tissues.

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Chronic Inflammation (Parasites)

Long-term inflammation can lead to cancer, like in some parasite infections.

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Parasite Pathogenicity Factors

Characteristics that contribute to a parasite's ability to cause disease.

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Defense Evasion (Parasites)

Parasites use tricks to evade the host's immune system, including changing their surface antigens.

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Antigenic Variation

Parasites altering their surface proteins to avoid being recognized by the immune system.

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Molecular Mimicry

Parasites use host molecules to hide from the immune system.

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Antigenic Masking

Parasites covering themselves with host molecules to avoid immune response.

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Host Defense Disruption

Parasites damaging host immune responses.

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Establishment of Parasitic Disease

Parasites establish disease through toxic products, tissue damage, and immune responses.

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Parasite Attachment

Parasites attach to host cells or organs to begin infection.

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Replication (Parasites)

Parasites multiply; this is crucial for infection establishment.

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Immune Evasion

Parasites avoid detection by the host's immune system.

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Tissue Damage (Parasites)

Parasites can harm tissues through toxins or, simply, physical presence.

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Adherence

The process by which a parasite attaches to host tissues, the initial step in infection.

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Pathogenicity of Parasites

Parasite factors that cause disease: attachment, replication, and tissue damage.

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Protozoan Replication

Protozoans (single-celled parasites) replicate inside or outside host cells.

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Helminth Replication

Helminths (worms) typically don't replicate in the same way as protozoa.

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Tissue Tropism

Parasite preference for specific host tissues or organs.

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Mechanical Blockage

Some parasites physically block organs or tissues.

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Parasite Size and Damage

The physical size or presence of a parasite can directly harm organs or tissues.

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Study Notes

College of Medicine, King Faisal University

  • The College of Medicine is part of King Faisal University.
  • The college was established in 1975 (1395).

Parasite Pathogenicity

  • Parasites can cause chronic infections lasting months to years.
  • Repeated exposure leads to an increasing parasite load.
  • Pathogenesis of protozoan and helminthic diseases is variable.
  • Many parasites aren't highly virulent (not very harmful).
  • Some parasites can't replicate within the host.
  • Some parasites can have both characteristics.

Factors Contributing to Parasite Severity

  • Infecting dose
  • Number of organisms acquired over time
  • Parasitic infections are often chronic, lasting months to years.

Factors Associated With Parasite Pathogenicity

  • Infective dose and exposure
  • Penetration of anatomic barriers
  • Attachment
  • Replication
  • Cell and tissue damage
  • Disruption, evasion, and inactivation of host defenses

Parasite Entry Routes

  • Parasites are usually exogenous to the human host.
  • Entry occurs through ingestion or direct penetration of anatomic barriers.
  • Some parasites have active mechanisms to invade the host.

Parasite Ports of Entry

Route Examples
Ingestion Giardia spp., Entamoeba histolytica, Cryptosporidium spp., cestodes, nematodes
Direct penetration Malaria, Babesia spp., Filaria, Leishmania spp., Trypanosomes
Arthropod bite
Transplacental penetration Toxoplasma gondii
Organism-directed penetration Hookworm, Strongyloides spp., schistosomes

Learning Objectives

  • Students should know factors important in parasite pathogenicity.
  • Students should differentiate between common parasite entry modes.
  • Students should describe three pathologic mechanisms in parasitic diseases.

Parasite Penetration - Example: Hookworms

  • L3 larvae enter lungs, causing cough.
  • L3 larvae penetrate the skin, causing "ground itch".
  • L3 larvae enter the bloodstream.
  • L3 larvae migrate to grass.

Parasite Inoculum Examples

  • Mosquito: Malaria
  • Sand fly: Leishmaniasis

Question 1

  • Which protozoan is primarily transmitted by sexual contact?
  • Answer: Trichomonas vaginalis

Question 2

  • By what route is Schistosoma haematobium transmitted?
  • Answer: Skin penetration by cercariae

Pathologic Mechanisms by Protozoa

  • E. histolytica: Degrades epithelial basement membrane and cell-anchoring proteins.

Damage by Helminths

  • Direct damage can occur from:
    • Mechanical blockage of internal organs.
    • Pressure exerted by growing parasites.

Other Pathologic Mechanisms

  • Helminth migration through tissues can damage, and induce hypersensitivity.
  • Chronic inflammation around parasites can cause carcinomas.

Establishing Parasitic Disease

  • Elaboration of toxic products
  • Mechanical tissue damage
  • Immunopathologic reactions

Mechanisms Parasites Use to Damage Host Tissues

  • Blockage of internal organs
  • Pressure atrophy
  • Migration
  • Immunopathology (hypersensitivity, autoimmunity, protein-losing enteropathies, metaplastic changes)

Factors Important For Parasite Pathogenicity (Disruption, Evasion & Inactivation of Host Defenses)

  • Antigenic Variation: Surface antigen variation helps parasites evade host immune responses (e.g., malaria, Giardia).
  • Molecular Mimicry: Parasite antigens mimic host antigens, reducing antibody response (e.g., malaria, trypanosomes).
  • Antigenic Masking: Parasites acquire host molecules to hide from the immune system (e.g., some schistosomes and hydatid cyst).
  • Intracellular Location: Avoiding host defenses (e.g., Toxoplasma, Plasmodium, Leishmania).
  • Immunosuppression: Suppressing host immune responses (e.g., Trypanosomes, Plasmodium spp.).

Infection - Processes

  • Parasites attach to host tissue (adherence).
  • Replication and colonization (occurs in protozoa).
  • Life cycle plays a role in their survival.

Concluding Questions

  • Which disease is transmitted by a gastropod vector?
  • Answer: Schistosomiasis

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Parasite Pathogenicity PDF

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