Infection_Infectious Disease and Epidemiology.pptx

Module Overview

  • Course: Microbiology for Health Sciences (BIOL 2420)

  • Module Title: Infection, Infectious Disease, and Epidemiology

  • Instructor: P. Afshar

Objectives of Module 4

  • Examine Symbiotic Relationships: Explore various forms of interactions between microbes and hosts.

  • Compare Normal Flora: Differentiate between types of normal flora and their potential transformation into opportunistic pathogens.

  • Describe Steps in Microbial Invasion: Outline the steps involved in microbes invading and establishing themselves in hosts.

  • Define Pathogens: Understand pathogens and identify virulence factors that infectious agents utilize.

  • Modes of Transmission: Learn about the different ways infectious diseases are transmitted.

  • Health Care-Acquired Infections (HAIs): Recognize various types of HAIs and the initiating factors involved.

Symbiotic Relationships

  • Definition: Symbiosis is defined as "to live together." Humans host numerous microorganisms, forming symbiotic relationships.

  • Types of Symbiosis:

    • Mutualism: Both organisms benefit.

    • Commensalism: One organism benefits, and the other is not affected.

    • Parasitism: One organism benefits at the expense of the other.

Normal Microbiota in Hosts

  • Terminology: Also referred to as normal flora or indigenous microbiota.

  • Function: Microbiota colonize body surfaces without normally causing disease.

  • Types of Microbiota:

    • Resident Microbiota: Permanent occupants that generally do not cause disease.

    • Transient Microbiota: Temporary occupants that cannot persist due to competition, elimination, or body changes.

Acquisition of Normal Microbiota

  • Axenic Womb: Development occurs free of microorganisms before birth.

  • Initial Colonization: Microbiota begin to populate during the birthing process and establish significantly during the first months of life.

  • Sources of Acquisition:

    • Mother's Birth Canal: Microbial exposure during delivery.

    • Breast Milk: Introduction of beneficial microbes to the colon.

    • Environmental Contacts: Interaction with people and objects leads to additional colonization.

Opportunistic Pathogens

  • Definition: Normal microbiota that can cause disease under certain conditions.

  • Conditions Leading to Disease:

    • Unusual Body Sites: Introduction to regions of the body where they do not normally reside.

    • Immune Suppression: Weakened host defenses.

    • Changes in Normal Microbiota: Imbalance allows some organisms to thrive at the expense of others.

Reservoirs of Infectious Diseases

  • Definition: Sites where pathogens are maintained, serving as sources of infection.

  • Types:

    • Animal Reservoirs: Transmission from animals to humans (zoonoses).

    • Human Carriers: Asymptomatic individuals who can transmit pathogens.

    • Nonliving Reservoirs: Contaminated water, soil, etc.

Types of Zoonoses

  • Transmission Methods: Zoonotic diseases can be acquired through direct contact, consumption of animals, or via bloodsucking insects.

  • Notable Zoonotic Diseases: Examples include malaria (Plasmodium spp.), rabies (Lyssavirus), and anthrax (Bacillus anthracis).

The Process of Infection

  • Contamination: Presence of pathogens on the body.

  • Infection: When pathogens multiply and evade the body's defenses.

  • Major Portals of Entry:

    • Skin

    • Mucous Membranes

    • Placenta

    • Parenteral Route (circumventing primary entry points)

The Role of Adhesion in Infection

  • Adhesion Mechanism: Microorganisms attach to host cells using specialized structures and proteins, aiding in colonization.

  • Effects of Adhesion: Inability to adhere renders pathogens harmless; some pathogens may form biofilms.

Virulence Factors of Infectious Agents

  • Pathogenicity: The ability of a microorganism to cause disease.

  • Virulence: The degree of pathogenicity.

  • Key Virulence Factors:

    • Adhesion factors

    • Biofilms

    • Extracellular enzymes

    • Toxins

    • Antiphagocytic factors

Stages of Infectious Disease

  • Key Stages:

    • Incubation Period: Initial infection without symptoms.

    • Prodromal Period: Mild symptoms emerge.

    • Illness: Most severe symptoms are present.

    • Decline: Symptoms begin to subside.

    • Convalescence: Recovery phase where symptoms fade.

Symptoms, Signs, and Syndromes

  • Symptoms: Subjective experiences reported by patients.

  • Signs: Objective evidence of disease.

  • Syndrome: Combination of signs and symptoms indicating a specific condition.

Portals of Exit for Pathogens

  • Definition: Pathogens can exit the host through various pathways, which often overlap with the portals of entry.

  • Examples of Exit Points: Include skin (via blood), digestive tract (feces), and respiratory system (secretions).

Modes of Transmission

  • Overview: Infection can be transmitted from reservoir to host through various means.

  • Types of Transmission:

    • Contact Transmission (Direct and Indirect)

    • Vehicle Transmission (Airborne, Waterborne, Foodborne)

    • Vector Transmission (Biological and Mechanical)

Classification of Infectious Diseases

  • Categories of Disease:

    • Acute, chronic, and latent diseases.

    • Communicable vs. noncommunicable diseases.

  • Specific Definitions: Terms such as systemic, local, primary, and secondary infections.

Epidemiology of Infectious Diseases

  • Frequency Tracking:

    • Incidence: New cases over a specific time.

    • Prevalence: Total cases over a specific time.

Hospital Epidemiology: Nosocomial Infections

  • Types of Nosocomial Infections:

    • Exogenous: Acquired from healthcare environment.

    • Endogenous: Originate from personal microbiota.

    • Iatrogenic: Result from medical interventions.