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Describe the evolutionary arms race between hosts and parasites. Why is it important to study?
- Parasites have evolved to exploit hosts' bodies and hosts have evolved immunity to control infections
- Immunological response of the host to the parasite and the parasite's evasion of these responses must be well understood to determine successful treatment methods
Resistance: the ability of the host to withstand a parasitic infection. May develop in several ways.
What are the three groups of host defense mechanisms w/ description? INCLUDE ALL IMPORTANT SUBGROUPS
- Barrier defense: Presence of some physical/chemical barrier to the parasite. 4 types...
- 1. Anatomic- skin and mucous membranes; ciliated epithelial cells in respiratory and GI tracts; saliva, tears, mucous secretions, etc
- 2. Physiologic- temperature, pH, oxygen, lysozymes, etc
- 3. Endocytosis/phagocytosis- non-specific cellular activities
- 4. Inflammatory responses- vasodilation and increased capillary permeability with resulting migration of phagocytic cells
- Constitutive defense: non-specific; directed toward general defense; provide general protection against invasion, colonization, infection, etc; may not be sufficient to protect against pathogens
- AKA natural/innate resistance
- Inducible defense: specific; must be induced or turned on by host exposed to pathogen; are not immediately available after exposure
Define: immune, immunity, acquired immunity
- Immune: the ability to resist infectious disease
- Immunity: relative state of resistance of the host to a specific pathogen
- Acquired immunity: inducible defenses that take time to develop after exposure.
Active immunity vs. passive immunity
- Active immunity: the host undergoes an immunological response and produces cells/factors responsible for the immunity.
- This immunity can persist a long time in the host (vaccines)
- eg. host produces its own Abs and/or lymphocytes.
- Passive immunity: the host acquires immune factors which were produced in another animal
- eg. no time for vaccination, direct injection required
- This immunity is short-lived (anti-venom)
Describe antigens and antibodies. Give details
- Antigen: chemical substances that stimulate the immune system in animals
- antigenic macromolecules (usually proteins) are present on parasites
- Antibody: Protein synthesized by WBC in response to a foreign substance (At)
- Can directly destroy, make easier for WBC to destroy, etc.
- Antibodies and Antigens interact to form an Ab-At complex
- *NOTE- Parasites can camouflage themselves to avoid antibody reactions
What is molecular mimicry? Give specific examples.
- Molecular mimicry: parasite produces host-like molecules on its surface (or covers itself with host molecules) and is accepted as a host cell.
- Trypanosoma- consistently express a new version of glycoprotein coat (VSG) (1/1000 at a time)
- Plasmodium- resides in RBC and synthesizes proteins that appear on the RBC surface causing the RBC to anchor to the walls of the blood vessel. This prevents the infected cell from entering and being processed by the spleen.
- Flukes- alter the behavior of their intermediate hosts in ways that increase their chances of moving on to a new definitive host (increased snail movement to attract birds)
What are the three types of destruction to host tissue w/ detail?
- Necrosis: degeneration and death of cells or tissues from infection; tissues have opaque appearance.
- encystment and calcification of Trichinella spiralis larvae in mammalian muscle cause tissue necrosis.
- Fatty degeneration: this condition results in deposition of abnormal amounts of fat in cells. This type of degeneration imparts a yellowish color to the cells and is common among parasite-laden liver cells.
- eg Plasmodium
- Albuminous degeneration: this condition results in swollen cells packed with albumin/fatty granules, indistinct nuclei, and pale cytoplasm. Affected organs can include liver, heart muscle, kidneys, etc
Define tissue transformation. What are the four types w/ examples?
- Tissue transformation: parasites lead to changes in the growth pattern of the affected tissue
- Hyperplasia: body repair activity follows shortly after parasitic infection and the resulting inflammation, Increased cell metabolism leads to increased cell division
- eg. Liver fluke Fasciola promotes bile duct's thickening due to excessive division of the epithelial cells
- Hypertrophy: an increase in cell or organ size due to presence of intracellular parasites
- Plasmodium causes enlargement of the host's parasitized red blood cells and the spleen
- Metaplasia: tissue conversion/transformation from 1 type to another
- eg. Lung fluke Paragonimus converts lung tissue into fibroblast
- Neoplasia: refers to abnormal cell growth in a tissue, forming a new structure (tumor).
- benign if localized ith no invasion of adjacent tissues
- malignant if invades adjacent tissues or metastasizes.
- eg. Blood fluke Schistosoma may cause cancer of the urinary bladder.
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