Disease-Producing Microorganisms and Infectious Disease Processes

Disease Terminology and Predisposing Causes

  • Definition of Disease: An abnormality of the structure or function of a part, organ, or system within the human body.

  • Etiology and Expression:

    • Disease may originate from known or unknown causes.

    • Disease may display marked variation in severity and overall effects on an individual.

  • Predisposing Causes of Disease:

    • Factors or conditions that increase the probability of a person becoming ill.

  • Pathogen:

    • Any disease-causing organism.

  • Normal Flora:

    • Definition: The populations of microorganisms that normally live on or in the human body.

    • Benefits and Value: They crowd out and prevent the growth and proliferation of harmful bacteria.


Microscopic illustration of a disease-causing pathogen

Microorganisms and Infectious Agents

  • Bacteria:

    • Characteristics: Tiny, single-celled organisms. They can be beneficial or harmful.

    • Morphological Classifications (Based on Shape and Arrangement):

    • Cocci: Round-shaped bacterial cells.

    • Bacilli: Straight, slender rod-shaped cells.

    • Curved Rods: Short rods with a slight curve.

    • Examples of Bacterial Diseases:

    • Rocky Mountain spotted fever: Transmitted by tick bites.

    • Diphtheria: Infection of the upper respiratory tract.

    • Cholera: Transmitted through contaminated water supplies.

    • Strep throat: Bacterial infection affecting the throat.

  • Viruses:

    • Characteristics: Extremely small, non-living agents that multiply only within living host cells.

    • Examples of Viral Diseases:

    • AIDS (Acquired Immunodeficiency Syndrome)

    • Influenza

    • Chickenpox

    • Measles

  • Fungi:

    • Characteristics: Eukaryotic organisms structurally similar to yeasts and molds.

    • Examples of Fungal Diseases:

    • Athlete's foot: Fungal skin infection of the foot.

    • Thrush: Fungal infection of the mucous membranes.

    • Pneumocystis pneumonia (PCP): A fungal lung infection.

    • Ringworm: Superficial fungal skin infection.

  • Protozoa:

    • Characteristics: Single-celled eukaryotic organisms that feed on other microorganisms.

    • Examples of Protozoan Diseases:

    • Malaria: Protozoan bloodstream infection.

    • African Sleeping Sickness: Transmitted via the bite of a tsetse fly.

    • Amebic dysentery: Severe intestinal infection.

  • Prions:

    • Characteristics: Infectious protein particles that cause other normal proteins to alter their shape and misfold.

    • Examples of Prion Diseases:

    • Mad Cow Disease: Transmissible spongiform encephalopathy.

Parasitic Worms (Helminths)

  • Infection vs. Infestation:

    • The presence of parasitic worms in a host body is designated as either an infection or an infestation.

  • Classifications and Specific Examples:

    • Roundworms:

    • Ascaris: Found in rural Asia; infects both the lungs and the intestines.

    • Pinworms: Highly common in children; reside in the digestive system and spread through touching the mouth.

    • Flatworms:

    • Tapeworm: Grows inside the intestines; transmitted through the ingestion of uncooked or undercooked meat.

Etiological Classification of Infectious Diseases

  • Bacterial Diseases (B):

    • Cholera

    • Diphtheria

    • Rocky Mountain spotted fever

  • Viral Diseases (V):

    • AIDS

    • Chickenpox

    • Influenza

  • Fungal Diseases (F):

    • Pneumocystis pneumonia (PCP)

    • Thrush

  • Protozoan Diseases (P):

    • African sleeping sickness

    • Malaria

Disease Processes, Infection Types, and Transmission Mechanics

  • Types of Infections:

    • Local Infection: An infection restricted to a small part of the body.

    • General or Systemic Infection: An infection that affects or spreads throughout the whole body.

    • Opportunistic Infection: An infection occurring in a person with a weak or compromised immune system.

  • Communicability:

    • Definition: A disease process is communicable if it can be spread from one person to another.

  • Modes of Transmission:

    • Direct Contact: Disease transmission occurring through physical contact (e.g., direct touching).

    • Indirect Contact: Disease transmission occurring through intermediary items or vectors (e.g., touching objects, consuming contaminated food or water, exposure to insects).

  • Roles in Pathogen Transmission:

    • Host: A living organism in or on which a parasite lives.

    • Carrier: An organism, environmental medium (such as air or water), or bodily fluid that carries and transmits a pathogen.

    • Vector: An insect or animal that transmits a disease from one host to another.

  • Body Portals of Entry and Exit:

    • Anatomical pathways through which pathogens enter into or exit from the body:

    • Skin

    • Respiratory system

    • Digestive system

    • Urinary system

    • Reproductive system