Mechanisms of Pathogenicity

1. Mechanisms of Pathogenicity

2. Define a Few Words: • Pathogen • Pathology • Pathologist • Pathogenicity • Pathogenesis

3. If a person is exposed to a pathogen, what are some reasons why they might not get sick?

4. 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.

5. Location of Infections • Localized Infection • Infection stays in one area • Systemic Infection • Infection spreads throughout body

6. 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

7. 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.

8. Latent Infections • An asymptomatic infection capable of manifesting symptoms under particular circumstances or if activated. • Ex. Chicken Pox – • Shingles www.nlm.nih.gov

9. Primary vs. Secondary Infections • Primary infections • First disease that results in another disease (secondary infection) • Secondary infections • The result of a primary infection

10. 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

11. 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.

12. Virulence Factors • Characteristics that allow a pathogen to attach, escape destruction, and cause disease.

13. How does a pathogen know what species to infect and what kind of cells to infect?

14. Attachment • Receptors • 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.

15. 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

16. Facultative Intracellular Pathogens • Capable of surviving in an intracellular and extracellular environment. • Mechanisms of survival • Ex. Mycobacterium tuberculosis www.sunysb.edu

17. 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

18. Flagella • Allow motile bacteria to infect areas that nonmotile bacteria cannot reach. • May be able for bacteria to avoid phagocytosis. biology.clc.uc.edu

19. 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.

20. Exoenzymes • Necrotizing Enzymes • Coagulase • Kinases • Hyaluronidase • Collagenase • Hemolysin • Lecithinase

21. 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.

22. 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.

23. 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.

24. The End