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What is the first stage of infectious disease before symptoms begin to appear?
Which type of disease develops quickly but lasts only a short duration?
What is the process by which pathogens are transmitted indirectly from host to host via fomites called?
Which of the following is an example of a portal of exit for pathogens?
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What is it called when a primary infection is followed by an opportunistic infection?
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Which of the following is a characteristic of communicable diseases?
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What term describes immunity present in most of a population?
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Which type of infection is characterized by pathogens being confined to a small area of the body?
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What type of interaction involves both species benefiting?
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Which body area is considered axenic?
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Which pathogens are classified as opportunistic pathogens?
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What does LD50 represent?
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What are symptoms in the context of disease?
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Which of the following is a correct step in Koch’s postulates?
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Which category of disease is caused by anatomical and physiological defects present at birth?
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What does the term etiology refer to in relation to diseases?
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What role do lymphocytes play in the immune response?
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What is the primary function of eosinophils?
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What is involved in the process of phagocytosis?
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What does interferon do in the immune response?
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Which white blood cells are characterized by staining lilac with a mix of acidic and basic dyes?
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Which of the following is NOT a sign of inflammation?
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What distinguishes the membrane attack complex (MAC) in relation to bacterial susceptibility?
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What is the primary indicator of eosinophilia?
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What is the definition of prevalence in relation to disease?
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Which of the following describes an epidemic disease?
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Which of the following is not a characteristic of innate immunity?
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What role does lysozyme play in the body's first line of defense?
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What is the primary function of the skin as a first line of defense?
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How does gastric juice contribute to the body's defenses?
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What is meant by sporadic disease?
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Which of the following contributes to hospital-acquired infections?
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What role do MHC class I molecules play in the immune system?
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Which type of cell is responsible for producing antibodies during the humoral response?
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What distinguishes IgG from other antibody classes?
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How do antibodies recognize and bind to specific antigens?
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What is the function of memory B cells in the immune response?
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Which cells are primarily involved in cell-mediated immunity?
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What is the primary function of natural killer (NK) cells?
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What characterizes the primary immune response compared to the secondary immune response?
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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
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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
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Skin:
- Physical barrier
- Provides a protective layer that prevents pathogens entering the body.
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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.
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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
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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.
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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)
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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
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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.
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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
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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
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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
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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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Test your knowledge about infectious diseases with this quiz. Explore stages of infection, types of diseases, and immune responses. Perfect for students studying biology or healthcare.
