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Define a Few Words: Pathogen Pathology Pathologist Pathogenicity Pathogenesis 4 Phases of an Infectious Disease 1. Incubation Period Time that elapses between the arrival of the pathogen and the onset of symptoms. 2. Prodromal Period Stage in which symptoms are not experienced but patient typically feels like they are “coming down with something.” 3. Period of Illness The time during which symptoms of a particular disease are present. 4. Convalescent Period The time in which patient recovers. Location of Infections Localized Infection Infection stays in one area Systemic Infection Infection spreads throughout body Disease Description Acute Disease Has a rapid onset, usually followed by relatively rapid recovery. Ex. influenza Subacute Disease Intermediate between acute and chronic diseases. Onset more rapid than a chronic disease but less suddenly than most acute diseases. Chronic Disease Slow onset and lasts a long time. Ex. Tuberculosis, syphilis Symptoms Versus Signs of a Disease Symptom of a Disease A subjective indication that a person is experiencing a disease. Symptomatic Disease Experience symptoms. Asymptomatic Disease Do not experience symptoms. Signs of a Disease An objective sign of a disease. Latent Infections An asymptomatic infection capable of manifesting symptoms under particular circumstances or if activated. Ex. Chicken Pox – Shingles www.nlm.nih.gov Primary vs. Secondary Infections Primary infections First disease that results in another disease (secondary infection) Secondary infections The result of a primary infection Steps in the Pathogenesis of Infectious Diseases 1. Entry 2. Attachment 3. Multiplication 4. Invasion 5. Evasion of Host Defenses 6. Damage to Host Tissue Virulence Can use this word in 2 ways: 1. Can say that a microorganism is virulent or avirulent. Ex. Different strains of Corynebacterium diphtheriae (strains that produce diphtheria). Can say that one pathogen is more virulent than another pathogen. Ex. Different strains of Streptococcus pyogenes. Virulence Factors Characteristics that allow a pathogen to attach, escape destruction, and cause disease. Receptors Attachment Molecule on host cell that are recognized by the pathogen. Pathogen binds to host cell receptor. Adhesins Molecule on pathogen that recognizes and binds to the host cell receptor. Bacterial Pili Long, thin, hair-like, flexible projections on pathogen (composed mostly of proteins) that allows it to bind to host cell. Obligate Intracellular Pathogens Pathogens must live within host cells to survive and multiply. Ex. Rickettsias infect endothelial cells and vascular smooth muscle cells. www.cals.ncsu.edu www.microbelibrary.org Facultative Intracellular Pathogens Capable of surviving in an intracellular and extracellular environment. Mechanisms of survival Ex. Mycobacterium tuberculosis www.sunysb.edu Capsules Encapsulated bacteria are often harder to engulf by phagocytic white blood cells because they lack surface receptors. Phagocytes have difficulty engulfing this bacteria. www.cbc.ca Flagella Allow motile bacteria to infect areas that nonmotile bacteria cannot reach. May be able for bacteria to avoid phagocytosis. biology.clc.uc.edu Exoenzymes Major mechanism by which pathogens cause disease. They are produced by a pathogen. Enables pathogen to evade host defense mechanisms, invade, or cause damage to body tissues. Exoenzymes Necrotizing Enzymes Coagulase Kinases Hyaluronidase Collagenase Hemolysin Lecithinase Toxins Poisonous substances that are produced by a microorganism that often cause disease. 2 categories of toxins: 1. endotoxins Part of cell wall of gram-negative bacteria that can cause problems. 2. exotoxins Toxins produced within cells and then released from the cells. Endotoxins Ex. Septicemia caused by gram-negative bacteria. Caused by the lipid portion of its cell wall which is the endotoxin. Causes chills, fever, extreme exhaustion, and possibly septic shock. Exotoxin Poisonous proteins produced by pathogens. Often named for their target organs. Ex. Neurotoxins Affect the central nervous system. Ex. Clostridium tetani Ex. Enterotoxins Toxins that affect the gastrointestinal tract. Often cause diarrhea and vomiting. Ex. Salmonella spp.
