Pathogens and Immune Disorders

Pathogens

  • Pathogens are microorganisms that cause disease.
  • Types of pathogens:
    • Bacteria
    • Viruses
    • Fungi
    • Protozoa
    • Helminths (worms)
    • Ectoparasites (insects)

Bacteria

  • Single-celled organisms that can reproduce independently.
  • Examples:
    • E. coli (urinary tract infections)
    • Staphylococcus aureus (skin infections)
  • Treatment: Antibiotics (if not resistant).

Viruses

  • Not cells; require a host to replicate.
  • Hijack a cell's machinery.
  • Examples:
    • COVID-19
    • Rhinovirus (common cold)
    • Influenza
    • Herpes simplex
    • HIV
  • Treatment: Supportive care, some antivirals, and vaccines.

Fungi

  • Single-celled (yeast) or multicellular (mold).
  • Thrive in moist areas.
  • Examples:
    • Tinea
    • Candida (yeast)
    • Aspergillus
  • Treatment: Antifungals.

Parasites

  • Protozoa (e.g., Giardia, amoebas)
  • Helminths (worms, e.g., pinworms, tapeworms)
  • Ectoparasites (insects, e.g., lice)
  • Treatment: Antiparasitic medications.

Prions

  • Brief mention of prions (e.g., Creutzfeldt-Jakob disease, mad cow disease).

Antibiotic Resistance

  • Bacteria change, making antibiotics less effective.
  • Causes:
    • Overuse of antibiotics (e.g., for viral infections)
    • Use in livestock and agriculture
    • Not completing the full course of antibiotics
    • Inconsistent dosing
  • Consequences:
    • Harder to treat infections
    • Need for stronger, more toxic, and expensive drugs
    • Longer hospital stays, complications, and death
  • Common resistant bacteria:
    • MRSA (methicillin-resistant Staphylococcus aureus)
    • Resistant tuberculosis
    • Vancomycin-resistant bacteria

Testing for Microbes

  • Obtain a sample based on the patient's presentation (e.g., throat swab, sputum, urine, blood).
  • Use proper technique to avoid contamination.
  • Gram stain: Classifies bacteria quickly.
    • Gram-positive: Thick cell wall, stains purple (e.g., Streptococcus, Staphylococcus).
    • Gram-negative: Thinner wall, outer membrane, stains pink (e.g., E. coli, Pseudomonas).
  • Culture and sensitivity:
    • Grows microorganism from the sample to identify the specific bacteria.
    • Tests which antibiotics are effective.
    • Crucial to obtain samples before starting antibiotics.
    • Guides treatment plans based on results.

Tuberculosis (TB)

  • Bacterial infection caused by Mycobacterium tuberculosis.
  • Affects the lungs but can spread to other organs.
  • Types:
    • Latent TB: Not contagious, contained by the immune system, positive TB skin test.
    • Active TB: Contagious, immune system weakens, TB spreads.
  • Risk factors:
    • Homelessness
    • Incarceration
    • HIV
    • Travel to high-risk areas
  • Highly contagious through airborne droplets.
  • Use airborne precautions (N95 masks, negative pressure rooms).
  • Long-term treatment (6-9 months).
  • Treatment compliance using DOT (directly observed therapy) to prevent drug resistance.

Urinary Tract Infections (UTIs)

  • Upper tract (pyelonephritis: ureters and kidneys) vs. lower tract (cystitis: bladder and urethra).
  • Lower UTIs (cystitis/bladder infection):
    • Symptoms: dysuria, urgency, frequency, cloudy urine, hematuria.
    • No fever or systemic symptoms.
    • Exception: Elderly patients may present with confusion.
  • Upper UTIs (pyelonephritis/kidney infection):
    • Symptoms: dysuria, frequency, urgency, fever, flank pain, nausea, vomiting.
    • Abrupt onset.
  • Untreated bladder infections can lead to kidney infections and urosepsis (life-threatening).
  • Risk factors for complicated UTIs:
    • Diabetes, HIV, immunodeficiency
    • Anatomical abnormalities
    • Catheter use
  • Nursing Considerations:
    • Obtain urine sample before antibiotics.
    • Educate on hydration and hygiene (wiping front to back).
    • Monitor for worsening symptoms.
    • Consider UTI in elderly patients with confusion.

Viruses

  • Genetic material (DNA or RNA) inside a protein coat.
  • Cannot survive or reproduce on their own; must invade a host cell.
  • Viral Life Cycle:
    • Attachment: Virus binds to specific receptors on host cell.
    • Penetration: Virus enters cell via fusion or endocytosis.
    • Uncoating: Virus releases genetic material from protein shell.
    • Replication: Virus uses host cell enzymes to copy viral genetic material.
    • Assembly: New viruses are assembled.
    • Release: New viruses are released, often destroying the host cell.
  • Antibiotics do not work against viruses.
  • Antiviral medications target specific viral processes (e.g., acyclovir, amantadine).
  • Vaccines are the best way to prevent viral infections.
  • Viruses can cause acute, chronic, or latent infections.
HIV (Human Immunodeficiency Virus)
  • Attacks the immune system, specifically CD4 cells (T helper cells).
  • Retrovirus: Inserts RNA into host DNA, becoming a permanent part of the cell.
  • Cannot be cured but can be controlled with antiretroviral therapy.
  • Weakens the immune system, making the body vulnerable to infections and cancers.
  • Stages:
    • Acute: Flu-like symptoms, high viral load, decreasing CD4 count.
    • Latent (Chronic HIV): Virus replicating slowly, no symptoms, CD4 count declining gradually.
    • AIDS (Acquired Immunodeficiency Syndrome): CD4 count less than 200 or presence of opportunistic infections.
  • Antiretroviral therapy suppresses viral replication and preserves CD4 cells.
  • Adherence to treatment is critical to prevent resistance.
  • Goal: Undetectable viral load (not contagious).
Opportunistic Infections in AIDS
  • Pneumocystis jirovecii pneumonia
  • Thrush (Candida infection in the mouth)

Fungi

  • Yeast and molds are normal flora but can cause problems if they overgrow.
  • Categories:
    • Superficial (dermatophytes): Skin, mouth, vagina (e.g., tinea, candida).
    • Deep: Organs (systemic), usually indicates an immunity issue.
  • Superficial Fungal Infections:
    • Tinea (ringworm, athlete's foot)
    • Candida (yeast infections in mouth, vagina, skin folds)
  • Deep Fungal Infections:
    • More serious, associated with immune compromise.

Parasites

  • Organisms that live on or in a host, benefiting at the host's expense.
  • Do not usually kill the host outright, but can cause chronic illness, malnutrition, and organ damage.
  • Common in underdeveloped countries, areas with poor sanitation and limited clean water, and tropical climates.
  • Transmission:
    • Fecal-oral (contaminated food or water), common with protozoa and helminths
    • Skin penetration (e.g., hookworms)
    • Insect bites (vector-borne, e.g., malaria, Lyme disease)
    • Close contact (ectoparasites, e.g., lice, scabies)
Types of Parasites
  • Protozoa
  • Helminths (worms)
  • Ectoparasites

Routes of Transmission for Infections

  • Aerosol/Airborne: Tuberculosis, measles, chickenpox
  • Droplets: Influenza, common cold, strep throat, COVID-19
  • Direct Contact: STIs, HIV, HPV, herpes, mono, hepatitis B and C
  • Fomites: Norovirus, MRSA, RSV (contaminated objects)
  • Fecal-Oral: Cholera, hepatitis A, rotavirus, polio, giardia
  • Vector-Borne: Malaria, Zika virus, dengue (insects carrying pathogens)
  • Zoonotic: Rabies, toxoplasmosis, avian flu (animals)

Stages of Infection

  • Exposure: Contact with the pathogen.
  • Incubation: Pathogens multiply; no signs and symptoms; can be contagious.
  • Prodromal: Feeling unwell; vague symptoms; very contagious.
  • Acute Illness: Maximum signs and symptoms; easiest stage to diagnose.
  • Convalescent: Recovery stage; symptoms improve; tissue repair.
  • Resolution: Pathogen eliminated; return to normal function.

Blood Cells

White Blood Cells
  • Granulocytes (neutrophils, eosinophils, basophils):
    • Neutrophils: First responders, kill with phagocytosis, increase in bacterial infections. Immature cells are called bands, shift.
    • Eosinophils: Important in parasitic and allergic reactions.
    • Basophils: Release histamine in allergic reactions (vasodilation, swelling). allergic responses like asthma, hives, anaphylaxis
  • Agranulocytes (lymphocytes, monocytes):
    • Lymphocytes: Adaptive immunity, increase in viral or fungal infections, and tumors (T cells, B cells, natural killer cells).
    • Monocytes: Become macrophages in tissues, phagocytosis, clean up dead cells and debris, connect innate and adaptive immunity. Are the bridge between innate and adaptive immunity.
      Those also secrete cytokines, long term immune responses
  • Platelets
  • Help in blood clotting.
Immune System Defenses
  • Three lines of defense:
    • Physical and chemical barriers (innate): Skin, mucus membranes, cilia, tears, saliva, sweat, stomach acid.
    • Inflammatory response (innate):
      • Phagocytes (neutrophils and macrophages)
      • Inflammation (redness, heat, swelling, pain)
      • Fever
      • Natural killer cells
    • Adaptive immune system: Specific antibodies, long-term immunity (lymphocytes).
Immunoglobulins
  • Also known as antibodies.
  • Types: IgG (long-term immunity, crosses placenta), IgA (mucous membranes), IgM (active infection), IgE (allergic reactions). Remembered using Game.
Hypersensitivity Reactions
  • Type I: Anaphylaxis (IgE-mediated).
  • Type II: Hemolytic anemia, Rh incompatibility (antibody-mediated).
  • Type III: Autoimmune diseases (antigen-antibody complexes).
  • Type IV: Delayed (T cell-mediated; e.g., tuberculosis test, poison ivy contact dermatitis).
Active and Passive Immunity
  • Active: Exposure to an antigen causes the body to produce its own antibodies.
  • Passive: Antibodies are given to the body without active exposure to an antigen (e.g., monoclonal antibodies, immunoglobulins, mother to baby).
Autoimmune Disease vs. Immunodeficiency
  • Autoimmune Disease: Immune system overreacts and targets the body's own tissues.
  • Immunodeficiency: Immune system is underactive or missing components, leading to increased susceptibility to infections.
Leukemia
  • Cancer of early blood-forming cells in the bone marrow.
  • Abnormal cells multiply rapidly and crowd out healthy cells.
  • Types: Acute or chronic (fast-growing vs. slow-growing); lymphoblastic (affecting lymphocytes) or myelocytic (affecting basophils, eosinophils, neutrophils).
  • The treatment does not target the cancer cells. Instead it is replaced and that can be done with the healthy donor to help the body restore.
    Lymphoproliferative disorders
  • Hodgkin vs non-Hodgins.
Lymphoma
  • Cancer of the lymphatic system, affecting lymphocytes.
  • Hodgkin Lymphoma: Contiguous spread from lymph node to lymph node, Reed-Sternberg cells present, better prognosis in younger patients.
  • Non-Hodgkin Lymphoma: Non-contiguous spread, extranodal involvement, worse prognosis, seen in older adults.