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Questions and Answers
Which factors are important for parasite pathogenicity?
Which factors are important for parasite pathogenicity?
What is one common mode of entry for many parasites into the human host?
What is one common mode of entry for many parasites into the human host?
Which of the following parasitic infections can last for months to years?
Which of the following parasitic infections can last for months to years?
How do many parasites actively invade the human host?
How do many parasites actively invade the human host?
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Which organism is primarily transmitted through direct skin penetration?
Which organism is primarily transmitted through direct skin penetration?
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Which of the following is NOT a common mechanism of parasitic disease pathogenesis?
Which of the following is NOT a common mechanism of parasitic disease pathogenesis?
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What route is primarily used for the transmission of Schistosoma haematobium cercariae?
What route is primarily used for the transmission of Schistosoma haematobium cercariae?
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Which protozoan is mainly transmitted through sexual contact?
Which protozoan is mainly transmitted through sexual contact?
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What is the initial step in the establishment of a parasitic infection?
What is the initial step in the establishment of a parasitic infection?
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Which statement accurately describes the replication process of protozoan parasites?
Which statement accurately describes the replication process of protozoan parasites?
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Which mechanism is primarily responsible for damage caused by helminthic parasites?
Which mechanism is primarily responsible for damage caused by helminthic parasites?
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Which pathogenic feature is associated with the parasite E.histolytica?
Which pathogenic feature is associated with the parasite E.histolytica?
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What is a common immunologic response to parasitic infections?
What is a common immunologic response to parasitic infections?
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What is a primary factor that determines where a parasite can survive in a host?
What is a primary factor that determines where a parasite can survive in a host?
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How do helminths contribute to conditions like elephantiasis?
How do helminths contribute to conditions like elephantiasis?
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What mechanism is not involved in establishing a parasitic disease?
What mechanism is not involved in establishing a parasitic disease?
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What is a distinction between the pathogenic mechanisms of protozoan and helminthic parasites?
What is a distinction between the pathogenic mechanisms of protozoan and helminthic parasites?
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Which organism's infection has been linked to carcinomatous changes in the bile ducts?
Which organism's infection has been linked to carcinomatous changes in the bile ducts?
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Which of the following describes a potential consequence of chronic inflammation due to parasites?
Which of the following describes a potential consequence of chronic inflammation due to parasites?
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What is a common characteristic of helminthic infections?
What is a common characteristic of helminthic infections?
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Which of the following methods do parasites use to evade host defenses?
Which of the following methods do parasites use to evade host defenses?
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What type of immunopathologic reaction is associated with Schistosoma infections?
What type of immunopathologic reaction is associated with Schistosoma infections?
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How do parasites typically cause tissue damage?
How do parasites typically cause tissue damage?
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Which route is NOT typically associated with Schistosoma species infections?
Which route is NOT typically associated with Schistosoma species infections?
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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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Description
Explore the complexities of parasite pathogenicity in this quiz. Understand how various factors influence the severity of parasitic infections and the potential entry routes of parasites into hosts. Test your knowledge on the chronic nature of these infections and the behaviors of different parasites.
