PBS 3.1.3

Infectious Diseases Overview

Goals

• Describe how infectious diseases can be transmitted

• Explain ways to stop the spread of infectious disease

• Summarize how our bodies can fight infection

• Use models and simulations to find trends in data

Key Concepts

Chain of Infection

• Susceptible Host: Vulnerable to infection

• Reservoir: Where an agent previously resided

• Chain of Command:

  • Agent

  • Reservoir

  • Portal of Exit

  • Mode of Transmission

  • Portal of Entry

  • Susceptible Hosts

  • Back to Agent

Modes of Transmission

• Direct Contact: Touching infected individual or exposed to bodily fluids

• Indirect Contact:

  • Inhaling infected particles

  • Touching infected objects

  • Being bitten by infected insects

Immune Response

Types of Immunity

• Immune System: Host’s defense mechanism

• Innate Immunity: Non-specific defenses present at birth

• Acquired Immunity: Specific defenses developed over time

  • Passive Immunity: Acquired from mother

Innate Immunity Components

• Tears: Kill invaders and wash them out

• Nasal Mucosa and Cilia: Trap invaders

• Digestive Enzymes: Help kill invaders

• Phagocytes: Consume and digest invaders

• Stomach Acid: pH of 2 kills invaders

• Normal Flora: Prevent invader attacks

Adaptive Immune Response

• Antigens: Foreign invaders

• T-Cells: Destroy infected cells

• B-Cells: Produce antibodies

Functions of Antibodies

• Block pathogen entry

• Prevent bacteria from using nutrients

• Bind toxins from pathogens

Types of Immunity

• Naturally Acquired Immunity: T-cells prevent re-infection

• Artificially Acquired Immunity: Via vaccines

Epidemiology

• Vaccine: Contains weakened/killed pathogens

• Herd Immunity: Majority vaccinated, some resistant to infection

• R-naught ($R_0$): Measurement of infectiousness

  • Formula: $R_0 = \frac{new,cases}{existing,cases}$