PRINCIPLES OF DISEASE AND PATHOGENESIS

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1. Distinguish between signs and symptoms of disease.
2. Define infectious, communicable and contagious diseases and give examples.
3. Define nosocomial infection and explain how nosocomial infections can be prevented.
4. Describe the 5 periods (stages) of a disease: incubation, prodromal, illness, decline, convalescence.
5. List Koch’s postulates, and summarize the limitations of Koch’s postulates.
6. Explain the difference between a pathogen’s infectious dose and lethal dose.
7. Distinguish between primary and opportunistic pathogens and give examples.
8. Define portal of entry, parenteral route, portal of exit.
9. Using examples, explain how microbes adhere to host cells.
10. Define the following types of infections: local, focal, systemic, primary, secondary
11. Explain why hyaluronidase, DNAase, phospholipase, collagenase and kinase are called “spreading factors.”
12. Differentiate between endotoxins and exotoxins, and give examples of each.
13. Define superantigen.
14. Using examples, explain how bacteria evade the immune system.
15. List the principle modes of disease transmission and give examples of each.
ANTIBIOTICS AND ANTIMICROBIAL RESISTANCE
1. Describe the various mechanisms of action associated with antibacterial drugs.
2. Describe the different mechanisms for drug resistance used by bacteria.
3. Investigate antibiotic-resistant “superbugs.”
BACTERIAL DISEASES
1. Know the major body regions that are colonized with normal flora (microbiota), and list some microorganisms normally found in each area.
2. For the following organisms, know where they are normally found, what diseases they cause, virulence factors and mode of transmission (epidemiology). Also know which organisms have vaccines:
• Staphylococcus aureus
• Streptococcus pyogenes (beta-hemolytic Group A Streptococci)
• Streptococcus mutans
• Streptococcus pneumonia
• Corynebacterium diphtheria
• Mycobacterium tuberculosis
• Bordetella pertussis
• Haemophilus influenza type B
• Neisseria meningitides
• Chlamydia trachomatis
• Neisseria gonorrhoea
• Escherichia coli
• Salmonella sp.
• Clostridium perfringens
• Clostridium difficile
• Clostridium botulinum
• Clostridium tetani
• Borrelia burgdorferi

ADAPTIVE IMMUNITY AND VACCINES
1. Differentiate between antibody-mediated (humoral) and cell-mediated immunity.
2. Define antigen and antibody.

 

Sample Solution

Distinguishing Signs and Symptoms of Disease

  • Signs: Objective indicators of disease that can be observed by a healthcare professional. Examples: fever, rash, swelling, abnormal blood test results.
  • Symptoms: Subjective experiences of disease reported by the patient. Examples: pain, fatigue, nausea, loss of appetite.

Infectious vs. Communicable vs. Contagious Diseases

  • Infectious Disease: Caused by a pathogenic organism (bacteria, virus, parasite, fungus).
  • Communicable Disease: Can be spread from an infected person or animal to another person or animal. (Not all infectious diseases are communicable. Some require specific modes of transmission, like tetanus from contaminated objects).
  • Contagious Disease: Highly transmissible communicable disease that spreads easily through casual contact. (Examples: common cold, influenza)

Nosocomial Infections

  • Nosocomial infection: An infection acquired in a healthcare setting (hospital, clinic) that wasn’t present upon admission.

Prevention:

  • Strict adherence to hand hygiene protocols by healthcare workers.
  • Proper disinfection of medical equipment.
  • Judicious use of antibiotics to minimize emergence of resistant bacteria.
  • Patient education on infection control practices.

Stages (Periods) of a Disease

  1. Incubation Period: The time between initial exposure to a pathogen and the ظهور (zuhūr) – appearance of symptoms. (No symptoms present)
  2. Prodromal Period: Vague, non-specific symptoms like fatigue, malaise, headache appear.
  3. Illness Period: Classic symptoms of the disease manifest.
  4. Decline Period: Symptoms begin to subside as the body fights the infection.
  5. Convalescence: Recovery period where the body regains strength and damaged tissues repair.

Koch’s Postulates

These postulates attempt to establish a causal link between a microorganism and a specific disease.

  1. The microorganism must be found in abundance in all cases of the disease and absent from healthy individuals.
  2. The microorganism must be isolated and grown in pure culture.
  3. The isolated microorganism must cause the disease when introduced into a healthy host.
  4. The microorganism must be re-isolated from the diseased host and be identified as the original organism.

Limitations:

  • Not applicable for all diseases (viruses don’t grow in pure culture, some diseases have complex causes beyond a single pathogen).
  • Ethical considerations prevent deliberately infecting healthy individuals.

Infectious Dose vs. Lethal Dose

  • Infectious Dose (ID): The minimum number of pathogen particles required to establish an infection in a susceptible host.
  • Lethal Dose (LD): The amount of a pathogen or toxin necessary to cause death in 50% of a test population (LD50).

Generally, the ID is much lower than the LD.

Primary vs. Opportunistic Pathogens

  • Primary Pathogens: Highly virulent organisms that can cause disease in healthy individuals. (Examples: Staphylococcus aureus, Streptococcus pyogenes)
  • Opportunistic Pathogens: Normally harmless organisms that can cause disease in individuals with compromised immune systems. (Examples: Pseudomonas aeruginosa, Candida albicans)

Portals of Entry, Parenteral Route, Portal of Exit

  • Portal of Entry: The body surface or opening through which a pathogen enters the host. (Examples: respiratory tract, digestive tract, skin)
  • Parenteral Route: Any route of entry that bypasses the skin and mucous membranes (injections, surgery)
  • Portal of Exit: The route by which a pathogen leaves the infected host and can potentially infect another individual. (Examples: respiratory droplets, feces, blood)

Microbial Adherence to Host Cells

  • Adhesins: Surface molecules on microbes that allow them to attach to specific receptors on host cells. (Examples: pili, fimbriae)
  • Biofilms: Communities of microorganisms attached to a surface and embedded in a self-produced matrix, making them more resistant to the immune system and antibiotics.

Types of Infections

  • Local Infection: Confined to a specific tissue or organ. (Example: skin abscess)
  • Focal Infection: Localized infection with surrounding inflammation. (Example: pneumonia)
  • Systemic Infection: Involves the entire body with widespread symptoms. (Example: sepsis)
  • Primary Infection: The initial infection caused by a specific pathogen.
  • Secondary Infection: A new infection that occurs during or following a primary infection, often due to opportunistic pathogens taking advantage of a weakened immune system.

Spreading Factors

These are enzymes produced by some pathogens that degrade host tissues and facilitate their invasion and spread:

  • Hyaluronidase: Degrades hyaluronic acid, a

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