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76 Cards in this Set
- Front
- Back
What are the principal portals of entry?
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1) Mucous membranes
2) Skin 3) Direct deposition beneath the skin or membranes (the parenteral route) |
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Portals of Entry: Through the Mucous Membrane
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1) bacteria and viruses penetrate the mucous membrane of the respiratory tract. The respiratory tract is the easiest and most frequently traveled portal for infectious disease.
2) The gastrointestinal tract is accessed through food and water and contaminated fingers. Most are killed by hydrochloric acid and enzymes in the stomach or bile in the small intestines. 3) Genitourinary Tract is the tract for pathogens contracted sexually. Some STIs may penetrate an unbroken mucous membrane |
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Portals of Entry: Through the skin
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Unbroken skin is almost impenetrable by most microorganisms. Some microbes gain access through openings such as sweat gland ducts and follicles.
Conjunctiva is a delicate mucous membrane that lines the eyelids and covers the white of the eyeballs. |
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Portals of Entry: The Parenteral Route
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Microorganisms gain access to the body when they are deposited directly into the tissues beneath the skin or into the mucous membranes when these barriers are penetrated or injured (punctures, bites, cuts, wounds, surgery, swelling, drying)
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Preferred Portal of Entry
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Pathogens have a preferred portal of entry that is key to their ability to cause disease. If they enter through a different portal, disease may not occur. (Ex. if swallowed Salmonella makes you ill, but if rubbed on skin there is no reaction)
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What is ID50?
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ID50 describes the virulence of a pathogen. Infectious Dose in 50% of the population.
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What is LD50?
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LD50 describes the potency of a pathogen. Lethal Dose for 50% of the population
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What does Adherence mean?
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The means of a of attachment that pathogens need to attach themselves to host tissues
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Adhesins
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Surface molecules on pathogen that allow for adherence
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Ligands
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Complementary surface receptors on host cells that Adhesins use to attach
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What are the principal portals of entry?
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1) Mucous membranes
2) Skin 3) Direct deposition beneath the skin or membranes (the parenteral route) |
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Portals of Entry: Through the Mucous Membrane
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1) bacteria and viruses penetrate the mucous membrane of the respiratory tract. The respiratory tract is the easiest and most frequently traveled portal for infectious disease.
2) The gastrointestinal tract is accessed through food and water and contaminated fingers. Most are killed by hydrochloric acid and enzymes in the stomach or bile in the small intestines. 3) Genitourinary Tract is the tract for pathogens contracted sexually. Some STIs may penetrate an unbroken mucous membrane |
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Portals of Entry: Through the skin
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Unbroken skin is almost impenetrable by most microorganisms. Some microbes gain access through openings such as sweat gland ducts and follicles.
Conjunctiva is a delicate mucous membrane that lines the eyelids and covers the white of the eyeballs. |
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Portals of Entry: The Parenteral Route
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Microorganisms gain access to the body when they are deposited directly into the tissues beneath the skin or into the mucous membranes when these barriers are penetrated or injured (punctures, bites, cuts, wounds, surgery, swelling, drying)
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Preferred Portal of Entry
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Pathogens have a preferred portal of entry that is key to their ability to cause disease. If they enter through a different portal, disease may not occur. (Ex. if swallowed Salmonella makes you ill, but if rubbed on skin there is no reaction)
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What is ID50?
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ID50 describes the virulence of a pathogen. Infectious Dose in 50% of the population.
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What is LD50?
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LD50 describes the potency of a pathogen. Lethal Dose for 50% of the population
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What does Adherence mean?
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The means of a of attachment that pathogens need to attach themselves to host tissues
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Adhesins
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Surface molecules on pathogen that allow for adherence
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Ligands
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Complementary surface receptors on host cells that Adhesins use to attach
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Biofilms
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Masses of bacteria that cling to surfaces, and take in a share nutrients. They multiply and secrete glycocalyx that further attaches the bacteria to each other and the surface (Ex. plaque on teeth, algae)
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Capsules
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Glycocalyx material that forms a capsule around bacterial cell walls. This property increases the virulence of the species. The capsule resists the host's body defenses by impairing phagocytosis.
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Cell wall components
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Some Cell walls in bacteria contain chemical substances that contribute to virulence. (Ex. M Protein and waxy lipids that help resist phagocytosis) or )
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Enzymes: Coagulases
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Bacterial enzymes that coagulate (clot) the fibrinogen in blood. The fibrin clot may protect the bacterium from phagocytosis and isolate it from other host defenses
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Enzymes
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The virulence of bacteria is often aided by enzymes. Enzymes are chemicals that can digest materials between cells and form or digest blood clots, among other functions
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Enzymes: Bacterial Kinases
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Bacterial enzymes that break down fibrin and thus digest blood clots formed by the body to isolate infection
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Enzymes: Hyaluronidase
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A bacterial enzyme that hydrolyzes hyaluronic, a type of polysaccharide that holds together certain cells of the body. Involved in tissue blackening. Also produced by some bacteria that cause gangrene. Can be used therapeutically, by mixing with a drug to spread the drug throughout the whole body tissue
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Enzymes: Collagenase
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Facilitates the spread of gangrene by breaking down collagen, which forms the connective tissue of muscles and other organs and tissues
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Enzymes: IgA Protease
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As a defense against adherence of pathogens to mucosal surfaces, the body produces a class of antibodies called IgA antibodies. Some pathogens produce IgA Protease which can destroy these antibodies.
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Antigenic Variation
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A process by which pathogens alter surface antigens to remain undetected by antibodies
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Penetration into the host cell Cytoplasm
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After pathogens attach by adhesins, the host cell activates factors that result in the entrance of bacteria into the cell.
Actin is a major component that is used by microbes to penetrate host cells. Invasins are surface protiens of some pathogens that rearrange actin filaments. This causes the host cell plasma membrane to resemble a splash of water, Membrane Ruffling |
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Siderophores
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Proteins secreted by pathogens to obtain free iron. When Iron is needed, siderophores are released into the medium where they take the iron from the iron transporters by binding the iron even more tightly than the transporters
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4 ways that pathogens damage host cells
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1) By using the host's nutrients
2) By causing direct damage in the immediate vicinity of the invasion 3) By producing toxins, transported by blood and lymph, that damage sites far removed from the original site of invasion 4) By inducing hypersensitive reactions |
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What is required for the growth of most pathogenic bacteria?
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Iron
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How do pathogens cause direct damage?
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They cause direct damage as they use the host cell for nutrients and produce waste products. Also, rupture cells, phagocytosis-like behavior, enzymes. Most damage, however, is done by toxins
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Exotoxins
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Toxins produced inside some bacteria as part of their growth and metabolism and are secreted by the bacterium into the surrounding medium or released following lysis. Exotoxins are proteins and many are enzymes that catalyze only certain biochemical reactions
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Antitoxins
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Antibodies produced by the body to provide immunity to exotoxins. Sometimes, Exotoxins no longer produce disease but still cause the body to produce antitoxins, these are called toxoids
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Exotoxins: A-B Toxins
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First toxins studied. Have two parts, A and B, which are both polypeptides. The A part is the active (enzyme) component. The B part is the binding component (Pg 435)
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Process of A-B Toxin
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1) Bacterium Produces and releases exotoxin
2) B (binding) component of exotoxin attaches to host receptor cell 3) A-B exotoxin enters host cell by endocytosis 4) A-B exotoxin enclosed in pinched-off portion of plasma membrane during pinocytosis 5) A-B components of exotoxin separate. The A component alters cell function by inhibiting protein synthesis. The B component is released from the host cell. |
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Exotoxins: Membrane-disrupting Toxins
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Cause lysis of host cells by disrupting their plasma membranes. Membranes disrupting toxins increase virulence by killing host cells, especially phagocytes and aiding the escape of bacteria trapped within phagosomes
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Leukocidins
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Membrane disrupting toxins that kill phagocytic white blood cells
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Hemolysins
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Membrane disrupting cells that destroy erythrocytes, also by forming protein channels.
Hemolysins produced by streptococci are called Streptolysins |
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Exotoxins: Superantigens
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Antigens (Bacterial proteins) that provoke a strong immune response. Specifically T cells.
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Cytokines
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Chemical proteins that regulate immune response and mediate cell to cell communication
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Representative Exotoxins: Diphtheria Toxin
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Release Exotoxin only when infected by lysogenic phage. Inhibits protein synthesis in eukaryotic cells using A-B mechanism
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Representative Exotoxins: Erythrogenic Toxins
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Streptococcus pyrogenes releases 3 cytotoxins, A, B and C. These are superantigens that damage the plasma membranes of blood capillaries under the skin and produce a red rash
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Representative Exotoxins: Botulinum Toxin
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An A-B neurotoxin. Works at the neuromuscular junction and prevents the transmission of nerve impulses from the nerve cell to muscles
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Representative Exotoxins: Tetnus Toxin
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An A-B Toxin of the central nervous system. Binds to nerve cells. The result is uncontrollable muscle contractions and convulsive symptoms. (ex. lockjaw)
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Representative Exotoxins: Vibrio Enterotoxin
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An A-B Toxin. Causes cells to secrete a large amount of fluid amd electrolytes. Normal muscular contractions are disturbed, leading to severe diarrhea that may be accompanied by vomiting
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Representative Exotoxins: Staphylococcal Enterotoxin
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A superantigen that causes toxic shock syndrome
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Endotoxins
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Part of the outer portion of the cell wall of gram-negative bacteria. Specifically, the lipid portion of the endotoxin, Lipid A. Endotoxins are released when gram-negative bacteria die and the cell wall is lysed. All endotoxins produce the same signs and symptoms. They cause macrophages to release cytokines in very high concentrations causing a variety of symptoms chills, fever, weakness, aches, shock or death. Can cause miscarriage
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What is the difference between exotoxins and endotoxins?
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Endotoxins are lipopolysaccharides
Exotoxins are proteins |
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What is the pyrogenic response? (4 steps)
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The fever (pyrogenic) response occurs in 4 stages.
1) A macrophage ingests a gram-negative bacterium 2) The bacterium is degraded in a vacuole, releasing endotoxins that induce the macrophage to produce cytokines Interleukin-1 (IL1) and tumor necrosis factor alpha (TNF@) 3) The cytokines are carried via blood to the hypothalamus a temperature control center of the brain. 4) The cytokines induce the hypothalamus to release lipids called prostaglandins, which reset the thermostat in the hypothalamus at a higher temperature. The result is fever. |
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Shock
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Any life threatening decrease in blood pressure
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Septic shock
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Shock caused by bacteria
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What are common viral mechanisms for invading host cells?
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1) Viruses can penetrate and grow inside host cells where immune system components can't reach them. They gain access through attachment sites
2) Mimic substances useful to cells to gain access. 3) Hide attachments from immunity cells and attack immunity cells (HIV) |
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Cytopathic Effects (CPE)
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The visual effects of viral infection
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Cytocidal effects
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The cytopathic effects that result in cell death
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Noncytocidal effects
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The cytopathic effects that result in damage to cells but NOT death
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What are the 9 Cytopathic effects of viral infections?
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1) Cytocidal viruses cause the macromolecular synthesis (mitosis) within a host cell to stop. (ex herpes)
2) Cause the cells lysosomes to release their enzymes, resulting in destruction of the intracellular contents and host death 3) Inclusion bodies are found in infected cells (sometimes viral parts). They are used to help identify the virus causing infection. 4) Several adjacent cells merge to form a very large multinucleated cell called a Syncytium 5) Some result in changes to host cell's function, w/ no visible changes to infected cells 6) Some virus infected cells produce interferons. These protect neighboring cells from infection by sending a warning 7) Many viral infections induce antigenic changes on the surface of infected cells. These changes illicit a host response against the cell 8) Some induce chromosomal changes in the host cell 9) Many infected cells lose contact inhibition |
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Examples of viral Cytopathic Effects
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Poliovirus - Cytocidal
Papovavirus - Acidophilic inclusion bodies in nucleus Adenovirus - Basophilic inclusion bodies in nucleus Rhabdovirus - Acidophilic inclusion bodies in nucleus Measles - Cell fusion Polymavirus - transformation HIV - Destruction of T cells |
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Pathogenic Properties: Fungi
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Fungi do not have a well defined set of virulence factors. Some have metabolic processes that are toxic. Chronic fungal infections.
Some cause skin infection Some inhibit protein synthesis |
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Fungal Toxins: Ergot
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The hallucinogenic toxin. Natural LSD
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Fungal Toxins: Aflatoxin
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Carcinogenic toxin
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Fungal Toxins: Mycotoxin
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Mushroom toxin Ex. phalloidin and amanitin, known as deathcap. Potent toxins that result in death
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Pathogenic Properties: Protozoa
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The presence of Protozoa and their waste products often produces disease symptoms
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Protozoa toxins: Giardia
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Attaches to host cell by a sucking disc and digests the host cells and fluids. Causes diarrhea.
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Protozoa Toxins: Trypanosoma
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Causes african sleeping sickness. Changes it's antigen to fool body defenses
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Pathogenic Properties: Helminths
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Use host tissue for their own parasitic growth and produce large parasitic masses
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Helminth Toxins: Wuchereria bancrofti
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Causative agent of elephantiasis. The parasite blocks lymphatic circulation and causes accumulation and massive swelling in legs.
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Algae Toxins: Alexandrium
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Important because they produce Saxitoxin. In shellfish/mollusks. Shell fish poisoning similar to Butulism
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Portal of Entry
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Microbes enter the body through a preferred portal of entry to cause ideal pathogenicity
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Portals of Exit
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Pathogens leave the body through secretions, excretions, discharges, or shed tissues. Most common are the respiratory and gastrointestinal tracts.
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Portals of Exit: Respiratory Tract
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One of the most common portals of exit. Pathogens are often dislodged through coughing or sneezing
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Portals of Exit: Gastrointestinal Tract
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Urine and feces
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Portals of Exit Chart 15.9 pg. 445
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Portals of Exit chart 15.9 pg. 445
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