Immune Defenses and Infectious Diseases Study Guide

IMMUNE DEFENSES OF THE RESPIRATORY TRACT

Innate vs Adaptive Immunity

  • Innate Immunity: Components are preformed and do not require prior exposure for activation.

    • Components:

      • Nasal hairs: Trap particles and pathogens.

      • Mucus: Impedes pathogen movement and traps microorganisms.

      • Cilia (mucociliary escalator): Cells with hair-like structures that move mucus upwards to clear contaminants.

      • Lysozyme: An enzyme that breaks down bacterial cell wall components.

      • Lactoferrin: Binds iron, inhibiting bacterial growth.

      • Cationic antimicrobial peptides: Disrupt microbial membranes.

      • Macrophages: Phagocytic cells that engulf and destroy pathogens.

  • Adaptive Immunity: Requires time to develop following exposure to pathogens.

    • Components:

      • Secretory IgA: An antibody found in mucosal areas.

      • B-cells/antibodies: Produce antibodies specific to antigens.

      • T-cells: Mediate cellular immune responses.

      • Activated macrophages: Enhanced phagocytes upon activation by cytokines.

COMMON COLD CAUSES

  • Viruses causing common cold (All viral):

    • Rhinovirus: Most prevalent cause.

    • Coronaviruses, Adenoviruses, Coxsackieviruses, RSV (Respiratory Syncytial Virus): Notable viral pathogens.

OTITIS MEDIA vs OTITIS EXTERNA

Otitis Media (Middle Ear Infection)

  • Characteristics:

    • Typically follows a viral upper respiratory tract infection.

    • Pathogen transmission occurs via the Eustachian tube.

  • Common bacterial agents:

    • Streptococcus pneumoniae

    • Haemophilus influenzae

    • Moraxella catarrhalis

  • Risk factors: Children are more susceptible due to shorter, narrower, and more horizontal Eustachian tubes.

Otitis Externa (Swimmer's Ear)

  • Characteristics:

    • Infection of the outer ear canal.

  • Common organisms:

    • Staphylococcus aureus, Pseudomonas aeruginosa

  • Additional note: Earwax (sebum) provides antimicrobial activity.

DIPHTHERIA

Diphtheria Toxin Mechanism

  • Action:

    • ADP-ribosylates Elongation Factor-2: This inhibits protein synthesis leading to host cell death.

  • Pseudomembrane Formation:

    • Forms a thick membranous network in the throat that can obstruct the airway.

  • Vaccination: The DTP/DTaP vaccine covers:

    • Diphtheria (toxoid), Tetanus, Pertussis (acellular antigens).

SCARLET FEVER & RHEUMATIC FEVER

Rheumatic Fever

  • Pathogen: Antigen is M protein from Streptococcus which resembles heart tissue, leading to cross-reactive antibodies.

Scarlet Fever

  • Toxin: Erythrogenic/pyrogenic toxin, which acts as a superantigen.

  • Symptoms: Causes a sandpaper rash and strawberry tongue.

INFLUENZA

Viral Mechanisms

  • Hemagglutinin: Facilitates virion attachment to host cells.

  • Neuraminidase: Assists in the release of new virions from infected cells.

Antigen Variability

  • Antigenic Drift: Mutation in H/N genes leading to most seasonal strains.

  • Antigenic Shift: Genetic reassortment occurs only in cases of co-infection, producing new subtypes capable of causing pandemics.

Influenza Types

  • Influenza A: Affects humans and animals; associated with severe outbreaks, epidemics, and pandemics.

  • Influenza B: Strictly human pathogen; associated with seasonal outbreaks.

  • Influenza C: Generally mild, not associated with epidemics.

Treatment & Prevention

  • Neuraminidase Inhibitors:

    • Examples: Zanamivir, Tamiflu; block the release of new viruses.

  • Influenza Vaccines:

    • Traditional inactivated and FluMist vaccines are based on eggs; recombinant vaccines available for those with egg allergies.

RSV (Respiratory Syncytial Virus)

  • Most prevalent cause of respiratory infections in newborns.

  • Highest impact on children under 1 year old.

  • High-risk groups: Premature infants, elderly, and immunosuppressed individuals.

  • Pathology: Causes bronchiolitis leading to small airway obstruction.

COVID-19

  • Key Binding Site: Virus uses the ACE2 receptor. Found on epithelial and endothelial cells across various body systems including respiratory, cardiac, renal, and gastrointestinal systems.

PATHOGENS: VIRUSES, BACTERIA, OR FUNGI

Viruses

  • Major viral pathogens: Influenza, RSV, Rhinovirus, Adenovirus, Coronaviruses, Parainfluenza, SARS-CoV-2.

Bacteria

  • Notable bacterial pathogens include:

    • Group A Streptococcus (GAS), Streptococcus pneumoniae, Haemophilus influenzae, Cornebacterium diphtheriae, Bordetella pertussis, Mycoplasma, Legionella, Yersinia pestis, Francisella tularensis, Bacillus anthracis.

Fungi

  • Fungal pathogens include:

    • Histoplasma capsulatum, Pneumocystis jiroveci.

ACID-FAST BACTERIA

  • Types: Mycobacterium tuberculosis, Mycobacterium leprae.

Tuberculosis (TB)

Granuloma Formation

  • Function: Walls off TB organisms; this containment allows determination of latent TB infection.

  • Latent TB Location: Inside granulomas, primarily within lung macrophages.

Reactivation Factors

  • Factors leading to reactivation included:

    • Depressed immune system, HIV/AIDS, Old age, Corticosteroid use.

Mantoux Test (TST/PPD test)

  • Method: Uses purified protein derivative to detect induration and erythema responses.

Treatment Challenges

  • Notably slow-growing requiring a 6–9 month multi-drug therapy.

  • Drug-Resistant Strains: MDR-TB (Multi-drug resistant) and XDR-TB (Extensively drug resistant).

VECTORS

Plague

  • Vector: Fleas

  • Reservoir: Wild rodents.

Tularemia

  • Vectors: Fleas, ticks, mosquitoes.

MOST DEADLY FORMS OF INFECTION

  • Plague: Pneumonic form has >90% mortality without treatment.

  • Tularemia: Pneumonic form has a 30–60% fatality rate when untreated.

  • Anthrax: Inhalational form has ~100% fatality rate without early treatment.

PNEUMOCYSTIS

  • Organism: Pneumocystis jiroveci.

  • At-risk population: Common in AIDS patients and causes lethal pneumonia.

ruiATYPICAL PNEUMONIAS

  • Caused by Mycoplasma pneumoniae:

    • Characteristic known as "walking pneumonia"; it lacks a cell wall hence is resistant to penicillin.

  • Legionella pneumophila: Causes severe pneumonia, with water and amoebas as reservoirs; prevention includes managing hot water systems and employing UV or copper-silver ionization.

THEORY 21 — GI REVIEW

Pathogen Associations

  • Dental Caries: Caused by Streptococcus mutans.

  • Mumps: Caused by Rubulavirus.

  • Gastritis, Ulcers: Often attributed to Helicobacter pylori.

  • Bloody Diarrhea: Seen with EHEC, Shigella.

  • Infantile Diarrhea: Frequently caused by EPEC.

  • Traveler’s Diarrhea: Commonly associated with ETEC.

  • Food-borne Diarrhea: The most common is from Campylobacter; associated with Guillain–Barre syndrome.

  • Rapid Onset Food Poisoning:

    • Typical agents include Staphylococcus aureus, Bacillus cereus, Clostridium perfringens.

  • Salmonella enterica typhimurium causes gastroenteritis; Salmonella enterica typhi causes typhoid fever.

  • Cruise Ship Diarrhea: Commonly associated with Rotavirus and Norovirus.

MacConkey Agar

  • Characteristics: Selective for Gram-negative organisms and differentiates lactose fermenters (pink colonies) from non-fermenters (pale colonies).

Enterobacteriaceae Properties

  • General Features: Gram-negative rods, facultative anaerobes that can grow on bile salts.

  • Lactose fermenters are classified as coliforms.

Toxins

  • Rapid-onset food poisoning involves: Preformed toxins that are heat-stable, causing serotonin release which leads to vomiting and diarrhea.

  • Shiga Toxin: Blocks translation, damaging the intestinal epithelium resulting in bloody diarrhea.

  • Cholera Toxin/ETEC LT/ST: Increases levels of cAMP or cGMP, opening ion channels that lead to water loss and watery diarrhea.

  • C. diff: Often triggered by antibiotic treatments.

HEPATITIS

  • Vaccines Available: A & B; Hepatitis D requires co-infection with B for worse outcomes; Hepatitis C is a leading cause of liver transplants.

  • Schistosoma Target Organ: Primarily affects the liver within the portal venous system.

THEORY 22–23 STUDY GUIDE

THEORIES 22–23: CVS

Target Cells of Common Pathogens

  • Plasmodium: Targets Red Blood Cells (RBCs).

  • Hepatitis Viruses: Affect liver cells.

  • UPEC: Infects urinary tract epithelium.

  • HIV: Specifically targets CD4 T-cells.

HIV Mechanism of Immunodeficiency

  • Action: HIV infects and destroys CD4+ T cells, leading to loss of adaptive immune responses.

HIV Lifecycle Components

  • GP120: Facilitates viral attachment.

  • Reverse Transcriptase: Converts viral RNA into DNA.

  • Integrase: Inserts viral DNA into the host genome.

  • Protease: Processes viral polypeptides for assembly into new virions.

Highly Active Antiretroviral Therapy (HAART)

  • Definition: Multi-drug therapy designed to inhibit multiple steps of the HIV lifecycle to prevent the development of resistance.

TSST-1 Superantigen

  • Effects: Causes massive nonspecific T-cell activation, potentially leading to toxic shock syndrome.

Pathogens that Infect RBCs

  • Notable Pathogens:

    • Plasmodium: Causes malaria.

    • Bartonella: Associated with several diseases.

Most Common Bacterial Endocarditis Causative Agent

  • Agent: Staphylococcus aureus.

Routes of Transmission of Various Pathogens

  • Malaria: Transmitted by mosquito vectors.

  • HIV: Spread through sexual transmission, body fluids, and blood.

  • Epstein-Barr Virus (EBV): Transmitted via saliva.

  • Hemorrhagic Fevers: Spread by arthropods or contaminated food and fluids.

  • Brucellosis: Commonly contracted through contaminated food or dairy products.

  • Pasteurellosis: Associated with cat or dog bites.

  • Trench Fever: Spread by lice.

  • Q Fever: Transmitted by ticks.

  • Lyme Disease: Spread via ticks.

  • Ehrlichiosis: Also primarily transmitted by ticks.

  • Rocky Mountain Spotted Fever: Spread by tick vectors.

THEORIES 23 — UROGENITAL PATHOGENS

Clue Cells

  • Definition: Vaginal epithelial cells covered with bacteria commonly seen in bacterial vaginosis (BV).

Herpes Viruses

  • Types of Virus:

    • HSV-1: Causes cold sores.

    • HSV-2: Causes genital herpes.

    • VZV: Causes chickenpox and shingles.

    • EBV: Causes mononucleosis.

  • Characteristic: All herpes viruses cause lifelong latent infections with periodic reactivations.

Syphilis Stages

  1. Primary Stage: Characterized by a painless chancre.

  2. Secondary Stage: Notable rash appears, particularly on palms and soles.

  3. Tertiary Stage: Development of gummas and neurologic/cardiac damage.

HPV and Cervical Cancer

  • Association: Certain high-risk strains are linked to cervical cancer.

  • Vaccine: Gardasil-9 protects against nine strains of HPV, including both cancer-causing and wart-causing types.

Pathogen/Agent/Disease List

  • Staphylococcus aureus: Bacteria causing endocarditis.

  • EBV: Virus responsible for mononucleosis.

  • Yellow Fever: Virus linked to hemorrhagic fever.

  • Ebola: Virus causing severe hemorrhagic fever.

  • Lassa: Another virus associated with hemorrhagic fever.

  • Bartonella: Bacterial agent resulting in cat scratch disease.

  • Pasteurella: Bacteria responsible for infections from cat/dog bites.

  • Borrelia burgdorferi: Spirochete causing Lyme disease.

  • Rickettsia: Bacteria responsible for Rocky Mountain Spotted Fever (RMSF).

  • UPEC: Bacterial agent linked to urinary tract infections (UTIs).

  • Candida albicans: Fungi causing yeast infections.

  • Trichomonas vaginalis: Protozoan sexually transmitted organism associated with discharge.

  • Chlamydia trachomatis: Bacteria representing the most common STI.

  • Neisseria gonorrhoeae: Bacterial agent causing discharge-associated STI.

  • Treponema pallidum: Spirochete responsible for syphilis.

  • Haemophilus ducreyi: Bacteria associated with chancroid.

  • HSV-1/2: Viruses leading to cold sores and genital ulcers, respectively.

  • HPV: Human Papillomavirus linked to genital warts.