Infectious Diseases Overview
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Questions and Answers

What is the first stage of infectious disease before symptoms begin to appear?

  • Incubation period (correct)
  • Prodromal period
  • Illness
  • Convalescence

    • Which type of disease develops quickly but lasts only a short duration?

  • Chronic disease
  • Latent disease
  • Subacute disease
  • Acute disease (correct)

    • What is the process by which pathogens are transmitted indirectly from host to host via fomites called?

  • Droplet transmission
  • Indirect contact transmission (correct)
  • Vehicle transmission
  • Vector transmission

    • Which of the following is an example of a portal of exit for pathogens?

    <p>Mouth</p> Signup and view all the answers

    What is it called when a primary infection is followed by an opportunistic infection?

    <p>Secondary infection</p> Signup and view all the answers

    Which of the following is a characteristic of communicable diseases?

    <p>Spread easily from one host to another</p> Signup and view all the answers

    What term describes immunity present in most of a population?

    <p>Herd immunity</p> Signup and view all the answers

    Which type of infection is characterized by pathogens being confined to a small area of the body?

    <p>Local infection</p> Signup and view all the answers

    What type of interaction involves both species benefiting?

    <p>Mutualism</p> Signup and view all the answers

    Which body area is considered axenic?

    <p>Alveoli of the lungs</p> Signup and view all the answers

    Which pathogens are classified as opportunistic pathogens?

    <p>Normal microbiota that cause disease under certain circumstances</p> Signup and view all the answers

    What does LD50 represent?

    <p>Lethal Dose needed to kill 50% of a population</p> Signup and view all the answers

    What are symptoms in the context of disease?

    <p>Subjective characteristics of disease felt only by the patient</p> Signup and view all the answers

    Which of the following is a correct step in Koch’s postulates?

    <p>The agent must be isolated and grown outside the host</p> Signup and view all the answers

    Which category of disease is caused by anatomical and physiological defects present at birth?

    <p>Congenital</p> Signup and view all the answers

    What does the term etiology refer to in relation to diseases?

    <p>Cause of the disease</p> Signup and view all the answers

    What role do lymphocytes play in the immune response?

    <p>They are involved in adaptive immunity.</p> Signup and view all the answers

    What is the primary function of eosinophils?

    <p>They are toxic against parasites and helminths.</p> Signup and view all the answers

    What is involved in the process of phagocytosis?

    <p>Chemotaxis, adhesion, ingestion, maturation, and elimination.</p> Signup and view all the answers

    What does interferon do in the immune response?

    <p>It nonspecifically inhibits the spread of viral infections.</p> Signup and view all the answers

    Which white blood cells are characterized by staining lilac with a mix of acidic and basic dyes?

    <p>Neutrophils</p> Signup and view all the answers

    Which of the following is NOT a sign of inflammation?

    <p>Fatigue</p> Signup and view all the answers

    What distinguishes the membrane attack complex (MAC) in relation to bacterial susceptibility?

    <p>It targets gram-negative bacteria due to fewer layers of peptidoglycan.</p> Signup and view all the answers

    What is the primary indicator of eosinophilia?

    <p>Helminth infestation or allergies</p> Signup and view all the answers

    What is the definition of prevalence in relation to disease?

    <p>The total number of cases of a disease in a specific area during a specific time.</p> Signup and view all the answers

    Which of the following describes an epidemic disease?

    <p>A disease acquired by many people in a given area in a short time.</p> Signup and view all the answers

    Which of the following is not a characteristic of innate immunity?

    <p>Specific immunity to particular pathogens.</p> Signup and view all the answers

    What role does lysozyme play in the body's first line of defense?

    <p>It destroys the cell wall of bacteria.</p> Signup and view all the answers

    What is the primary function of the skin as a first line of defense?

    <p>To act as a physical barrier against pathogens.</p> Signup and view all the answers

    How does gastric juice contribute to the body's defenses?

    <p>By destroying most bacteria and toxins through its low pH.</p> Signup and view all the answers

    What is meant by sporadic disease?

    <p>A disease that occurs in sudden, isolated outbreaks.</p> Signup and view all the answers

    Which of the following contributes to hospital-acquired infections?

    <p>Inadequate hand hygiene practices.</p> Signup and view all the answers

    What role do MHC class I molecules play in the immune system?

    <p>Present antigens to T cells in all nucleated cells.</p> Signup and view all the answers

    Which type of cell is responsible for producing antibodies during the humoral response?

    <p>Plasma B cells</p> Signup and view all the answers

    What distinguishes IgG from other antibody classes?

    <p>It is the most common and longest-lasting antibody in circulation.</p> Signup and view all the answers

    How do antibodies recognize and bind to specific antigens?

    <p>By binding to the surface of antigens at respective amino acids.</p> Signup and view all the answers

    What is the function of memory B cells in the immune response?

    <p>To increase antibody response during the second encounter with an antigen.</p> Signup and view all the answers

    Which cells are primarily involved in cell-mediated immunity?

    <p>T lymphocytes</p> Signup and view all the answers

    What is the primary function of natural killer (NK) cells?

    <p>Destroy cells lacking MHC class I self-antigens.</p> Signup and view all the answers

    What characterizes the primary immune response compared to the secondary immune response?

    <p>It is less efficient and slower than the secondary response.</p> Signup and view all the answers

    Study Notes

    Types of Interactions

    • Mutualism: Both organisms benefit from the relationship
    • Commensalism: One organism benefits, the other is unaffected
    • Amensalism: One organism is harmed, the other is unaffected
    • Parasitism: One organism benefits at the expense of the other

    Axenic Areas of the Body

    • Axenic: Areas of the body that are normally free of microbes.
    • Examples: Alveoli of the lungs, kidneys

    Normal Microbiota

    • Staphylococcus is a common inhabitant of the nose and skin due to the salty environment.

    Pathogens

    • Opportunistic pathogens: Normal microbiota that cause disease under certain circumstances, such as weakened immune system.
    • True pathogens: Cause disease in healthy individuals.

    Animal Reservoirs

    • Rabies, giardia, malaria, and many viruses are spread by animal reservoirs.

    Infectious Disease

    • Lethal Dose 50 (LD50): The amount of a pathogen that kills 50% of a test population.
    • Infectious Dose 50 (ID50): The amount of a pathogen that infects 50% of a test population.

    Portals of Entry

    • Skin: Breaks in the skin can allow pathogens entry.
    • Mucous membranes: Line body cavities that are exposed to the environment.
    • Placenta: Can allow pathogens to cross from the mother to the fetus.
    • Parental route: Introduction of pathogens directly into tissues, often through a needle or wound.

    Definitions

    • Pathology: The study of disease.
    • Etiology: The cause of disease.
    • Infection: The invasion or colonization of the body by pathogens.
    • Disease: An abnormal state in which the body is not performing normal functions.
    • Morbidity: Disease.
    • Mortality: Death.

    Signs and Symptoms

    • Symptoms: Subjective characteristics of disease felt only by the patient, such as pain or nausea.
    • Signs: Objective manifestations of disease observed or measured by others, such as fever or rash.

    Koch's Postulates

    • Koch's postulates are a set of criteria that can be used to establish a causal relationship between a microbe and a disease.
    • The suspected causative agent must be found in every case of the disease and be absent from healthy hosts.
    • The agent must be isolated and grown outside the host.
    • When the agent is introduced to a healthy, susceptible host, the host must get the disease.
    • The same agent must be found in the disease experimental host.

    Categories of Diseases

    • Hereditary diseases: Caused by errors in genetic code received from parents.
    • Congenital diseases: Anatomical or physiological defects present at birth.
    • Degenerative diseases: Result from aging.

    Dinoflagellates

    • Some dinoflagellates produce a neurotoxin called saxitoxin, which causes paralytic shellfish poisoning.

    Stages of Infectious Disease

    • Incubation period: The time from infection to the first symptoms or signs of illness.
    • Prodromal period: General, mild symptoms, such as aches or malaise.
    • Illness: The stage when the most severe symptoms or signs of the disease appear.
    • Decline: The stage when the immune response peaks and symptoms begin to subside.
    • Convalescence: The stage when the body recovers fully and tissues are repaired.

    Portals of Exit

    • Ear: Pathogens can exit through the ear.
    • Broken skin: Pathogens can exit through breaks in the skin.
    • Skin: Pathogens can exit through sweat and sebum.
    • Anus: Pathogens can exit through feces.
    • Seminal vesicles: Pathogens can exit through semen.
    • Urethra: Pathogens can exit through urine.
    • Vagina: Pathogens can exit through vaginal secretions.
    • Mammary glands: Pathogens can exit through breast milk.
    • Mouth: Pathogens can exit through saliva, nasal secretions, and respiratory droplets.
    • Nose: Pathogens can exit through nasal secretions.
    • Eyes: Pathogens can exit through tears.

    Transmission of Disease

    • Contact transmission: The spread of pathogens from one person to another through direct contact, droplet transmission, or indirect contact.
      • Direct contact transmission: The spread of pathogens from one person to another through physical contact.
      • Droplet transmission: The spread of pathogens from one person to another through respiratory droplets.
      • Indirect contact transmission: The spread of pathogens from one person to another through contact with fomites, which are inanimate objects that can harbor pathogens.
    • Vehicle transmission: The spread of pathogens through air, water, food, or bodily fluids.
    • Vector transmission: The spread of pathogens through arthropods.

    Types of Vectors

    • Mechanical vectors: Carry pathogens on their bodies.
    • Biological vectors: Carry pathogens within their bodies.

    Terms

    • Acute disease: Symptoms develop rapidly but the disease lasts only a short time.
    • Chronic disease: Symptoms develop slowly.
    • Subacute disease: Intermediate between acute and chronic.
    • Latent disease: The causative agent is inactive for a time but then activates and produces symptoms.
    • Herd immunity: Immunity in most of a population.
    • Local infection: Pathogens are limited to a small area of the body.
    • Systemic (generalized) infection: An infection throughout the body.
    • Focal infection: Systemic infection that began as a local infection.
    • Primary infection: An acute infection that causes the initial illness.
    • Secondary infection: An opportunistic infection after a primary infection.
    • Subclinical disease: No noticeable signs or symptoms, also known as an inapparent infection.
    • Communicable disease: A disease that is spread from one host to another.
    • Contagious diseases: Diseases that are easily and rapidly spread from one host to another.
    • Noncommunicable disease: A disease that is not spread from one host to another.

    Predisposing Factors

    • Gender: Men and women may be more susceptible to certain diseases.
    • Inherited traits: Inherited traits, such as the sickle cell gene, can increase susceptibility to certain diseases.
    • Climate and weather: Climate and weather can affect the spread of certain diseases.
    • Fatigue: Fatigue can weaken the immune system and make people more susceptible to disease.
    • Age: Age can affect a person's susceptibility to disease.
    • Lifestyle: Choices such as smoking, drug use, and lack of exercise can increase susceptibility to certain diseases.
    • Nutrition: Poor nutrition can weaken the immune system.
    • Chemotherapy: Chemotherapy drugs can suppress the immune system.

    Incidence and Prevalence

    • Incidence: The number of new cases of a disease in a given area during a given period of time.
    • Prevalence: The total number of cases of a disease in a given area during a given period of time.

    Terms (Continued)

    • Sporadic disease: Disease that occurs only occasionally.
    • Endemic disease: Disease constantly present in a population.
    • Epidemic disease: Disease acquired by many people in a given are in a short time.
    • Pandemic disease: A worldwide epidemic.
    • Emerging infectious disease: Diseases that are new, increasing in incidence, or showing potential to increase in the near future.

    Hospital-Acquired Infections

    • Contributing factors include:
      • Healthcare workers transferring pathogens between patients
      • Overuse of antibiotics
      • Compromised immune systems of hospitalized patients
    • Prevention strategies include:
      • Handwashing
      • Proper disinfection and sterilization of equipment
      • *Isolation of patients with infectious diseases

    Innate Immunity

    • Immunity: The ability to ward off disease.
    • Susceptibility: Lack of resistance to a disease.
    • Innate immunity: Defenses against any pathogen; rapid, present at birth.
      • First line of defense: Barriers to entry, such as skin and mucous membranes.
      • Second line of defense: Leukocytes, inflammation, fever, and the complement system.
    • Adaptive immunity: Immunity or resistance to a specific pathogen; slower to respond, has a memory component.

    The First Line of Defense

    • Skin:
      • Physical barrier
      • Provides a protective layer that prevents pathogens entering the body.
    • Mucous membranes:
      • Line body cavities that are exposed to the environment, such as the respiratory tract, digestive tract, and urinary tract.
      • Secrete mucus, which traps pathogens and prevents them from entering the body.
    • Chemical factors: Substances that help to kill or inhibit the growth of pathogens.
      • Perspiration: Contains salt, which inhibits the growth of pathogens.
      • Sebum: Contains fatty acids that lower the pH of the skin, which inhibits the growth of pathogens.
      • Lysozyme: An enzyme that destroys bacterial cell walls.

    The Second Line of Defense

    • Lymphatic system: Consists of lymph, lymphatic vessels, lymphoid tissue, and red bone marrow.
      • Lymph carries microbes to lymph nodes, where lymphocytes and macrophages destroy the pathogen.

    Types of White Blood Cells

    • Neutrophils: Stain lilac with a mix of acidic and basic dyes; phagocytic; work in the early stages of infection.
    • Lymphocytes: Most involved in adaptive immunity; include T cells and B cells, as well as natural killer lymphocytes.
    • Monocytes: Leave the blood and mature into macrophages; phagocytic cells that devour foreign objects.
    • Eosinophils: Stain red/orange with acidic dye eosin; phagocytic; toxic against parasites and helminths.
    • Basophils: Stain blue with basic dye methylene blue; release histamine; work in allergic responses.

    Phagocytosis

    • Phagocytosis is the process by which cells engulf and destroy pathogens.
    • Steps:
      • Chemotaxis: Chemotactic factors, such as cytokines and complement proteins, attract WBCs.
      • Adhesion: Phagocytes adhere to pathogens.
      • Ingestion: Phagocytes engulf pathogens.
      • Maturation: Lysosomes fuse with phagosomes, forming a phagolysosome.
      • Killing: Enzymes and toxic chemicals destroy the pathogen.
      • Elimination: Phagocytosis is complete.

    Eosinophils and Natural Killer Cells (NK)

    • Eosinophils: Often indicative of a helminth infestation or allergies.
    • Natural killer lymphocytes (NK cells): Secrete toxins onto the surface of virally infected cells; membrane proteins.

    Interferon (IFN)

    • Interferon: Protein molecules released by host cells to nonspecifically inhibit the spread of viral infections.
      • Causes many symptoms associated with viral infections (malaise, muscle aches, chills, headache, fever).

    Complement

    • Complement: A set of serum proteins designated numerically according to their order of discovery.
    • Membrane attack complex (MAC): A complex of complement proteins that can kill bacteria by punching holes in their cell membranes. Gram-negative bacteria are more susceptible to MAC because they have fewer layers of peptidoglycan.

    Inflammation

    • Four signs of inflammation:
      • Redness (rubor or erythema): Due to increased blood flow to the site of infection.
      • Swelling (edema): Due to the accumulation of fluids in the tissues.
      • Pain (dolor): Due to the release of chemicals that stimulate pain receptors.
      • Heat (calor): Due to the increased blood flow to the site of infection.

    Diapedesis

    • Diapedesis: The process by which leukocytes move out of blood vessels and into tissues.

    Adaptive Immunity

    • Adaptive immunity is specific immunity that develops after exposure to a pathogen.
    • Components:
      • Humoral immunity: The production of antibodies by B cells.
      • Cell-mediated immunity: The activation of T cells.

    Antigen-Presenting Cells (APCs)

    • Antigen-presenting cells (APCs) are types of immune cells that capture, process, and present antigens to T cells.
    • Major Histocompatibility Complex (MHC) proteins:
      • MHC 1: Found on all cells except red blood cells (nucleated cells)
      • MHC 2: Found on antigen-presenting cells (APCs), including macrophages and dendritic cells.

    Humoral Immune Response

    • Humoral response: Responsible for keeping the body's fluids (humors) clear of pathogens.
      • Plasma B cells produce antibodies.
      • Memory B cells remember for future antibody attack.

    Antibodies

    • Antibodies are proteins that are also known as immunoglobulins.
    • Structure: Antibodies have a Y-shaped structure with two antigen-binding sites.
    • Antigen-binding sites: Each antigen-binding site is shaped to fit a specific epitope (a specific portion of an antigen).
    • Antigen specificity: Antibodies have antigen specificity, meaning that they will only bind to the specific antigen that they are shaped to fit.

    Antigen Recognition

    • Antibodies recognize antigens by binding to the surface of the antigen, specifically to amino acids that are brought together in the folded protein.

    Ways Antibodies Work

    • Antibodies can work in several ways:
      • Neutralize antigens by blocking their ability to bind to host cells.
      • Opsonization: Coat pathogens, making them easier for phagocytes to engulf.
      • Agglutination: Clump pathogens together, making them easier for phagocytes to engulf.
      • Antibody-dependent cell-mediated cytotoxicity: ADCC is a process in which NK cells and other cytotoxic cells kill target cells that are coated with antibodies.

    Five Classes of Antibodies

    • IgM: The first antibody produced during an immune response.
    • IgG: The most common and longest-lasting antibody; crosses the placenta to protect the fetus.
    • IgA: Associated with body secretions, such as saliva, tears, and breast milk.
    • IgE: Involved in response to parasitic infections and allergies.
    • IgD: Exact function is not known.

    Memory Cells

    • Memory cells are important because they provide immunity against a specific pathogen.
    • Memory response: The second exposure to an antigen is much faster and stronger than the primary response due to increased numbers of initial cells and quicker activation.

    Cell-Mediated Immunity

    • Cell-mediated immunity requires the direct involvement of T lymphocytes.
    • T cells act directly against:
      • Antigens
      • Infected host cells.
      • Abnormal host cells.
      • Protozoa
    • T cells secrete cytokines that act on other cells.
    • Sensitized T cells proliferate into long-lasting memory T cells.
    • Rely on T cell receptors instead of antibodies.

    Natural Killer Cells

    • NK cells are granular leukocytes that destroy cells that do not express MHC class I self-antigens, such as virally infected cells and cancer cells.

    Primary and Secondary Responses

    • Primary response: The first exposure to an antigen.
      • Small amounts of antibodies are produced.
      • May take days to produce enough antibodies to eliminate the antigen from the body.
    • Secondary response: The second exposure to an antigen.
      • Much faster and stronger than the primary response due to memory cells that are specific for the antigen.
      • Much larger amounts of antibodies are produced.

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