Comprehensive Guide to Immunology and Infectious Diseases

Posted on Aug 13, 2024 in Biology

Immunology and Infectious Diseases

Types of Immunity

Active Immunization

Natural Active Immunization

Occurs through natural exposure to pathogens.

Artificial Active Immunization

Achieved through vaccines.

Passive Immunization

Natural Passive Immunization

Occurs naturally, such as maternal antibodies transferred to a fetus.

Artificial Passive Immunization

Involves the injection of antibodies (e.g., antivenoms).

Types of Vaccines

  • Attenuated (Live) Vaccines: Contain live, weakened pathogens.
  • Inactivated (Killed) Vaccines: Contain killed pathogens or their components (often contain adjuvants).
  • Toxoid Vaccines: Contain inactivated toxins produced by pathogens.
  • Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: Contain pieces of the pathogen (e.g., protein subunits).
  • mRNA Vaccines: Contain messenger RNA that encodes antigens.

Serological Tests

Detect antibodies or antigens in blood. Serological tests have several uses:

  • Monitor the spread of infection within a population
  • Establish diagnosis of disease
  • Agglutination Tests: Detect the clumping of antigens and antibodies.
  • Titration: Method to measure antibody levels in blood sera.
  • Precipitation Tests: Detect soluble antigens and antibodies that form a precipitate (Immunodiffusion).
  • ELISA (Enzyme-Linked Immunosorbent Assay): Detects antigens or antibodies using enzyme-labeled components (serum antibodies).
  • Western Blot: Detects specific proteins using gel electrophoresis and antibodies.
  • Direct Fluorescent Antibody Tests: Identify the presence of antigen in a tissue (Diagnosis of rabies).
  • Turbidimetry: Measures the light passing through a solution.
  • Nephelometry: Measures the light reflected from a solution (used to quantify the amounts of proteins in serum).
  • Viral Hemagglutination Inhibition Test: Useful for viruses that aren’t cytopathic (Commonly used to detect antibodies against influenza, measles, and mumps).

Historical Milestones

  • The first vaccine was developed by Edward Jenner against smallpox.
  • The fusion of myelomas (cancerous plasma cells) with plasma cells results in hybridomas, the source of monoclonal antibodies, which can be used in passive immunization.

Key Concepts in Immunology

  • Cell-mediated immunity is a function of: T Lymphocytes.
  • IgG: The most prevalent class of antibody, is produced when a particular antigen is encountered again.
  • Cytotoxic T lymphocytes insert PERFORIN into the membranes of the cells they target as a first step in killing.
  • Class 1 MHC molecules are essential for the presentation of antigens to T-cells.

Mycology and Virology

  • Deuteromycetes have no sexual stage.
  • Virion: An infectious particle of protein and nucleic acid outside a host cell.
  • Envelope portion of an enveloped virus is composed of: Host cell membranes containing virus-encoded glycoproteins.
  • Viral Replication Cycle: Attachment, Entry, Synthesis, Assembly, Release.
  • Plaque Assays: Determining the density of phage in a culture.
  • Prions cause disease in mammals.
  • During latency, viral synthesis is suspended.

Respiratory System Infections

Upper Respiratory System

  • Nose
  • Nasal cavity
  • Pharynx
  • Uvula

Lower Respiratory System

  • Larynx
  • Trachea
  • Bronchi
  • Alveoli
  • Diaphragm (microorganisms are not present typically)

Bacterial Respiratory Infections

  • Streptococcus pyogenes: Causative agent of scarlet fever.
  • Streptococcal Respiratory Diseases:
    • Pathogenesis: Occurs when normal microbiota are depleted, a large inoculum is introduced, or adaptive immunity is impaired.
    • Epidemiology: Spread via respiratory droplets. Occurs most often in winter and spring.
  • Anthrax: Acquired by inhalation of endospores. Virulence factors are capsule and toxin.
  • Diphtheria: Presence of pseudomembrane.
  • Legionnaires’ Disease: Survives in domestic water sources, affects the elderly and smokers.
  • Pertussis: Whooping cough.
  • Klebsiella pneumoniae: Pneumonia symptoms with bloody sputum and chills.
  • Tuberculosis: BCG vaccine is available. Mycolic acid gives bacteria unique features.

Fungal Respiratory Infections

  • Blastomycosis: Flu-like, can produce lesions on the face and upper body.

Viral Respiratory Infections

  • RSV: Most common childhood respiratory disease.
  • Common Cold: Rhinoviruses are the most common cause.
  • Influenza: Hemagglutinin and neuraminidase, there are type A and B, sudden fever distinguishes from a cold.
  • HPS: Hantavirus transmitted from mice via inhalation.
  • SARS: High fever, shortness of breath, difficulty breathing.

Other Respiratory Conditions

  • Otitis Media: Severe pain in ears.
  • Bacterial Pneumonia: Diagnosed by identifying diplococci in sputum smears.
  • Mycoplasmal Pneumonia: Most common pneumonia in teenagers and young adults.

Gastrointestinal Infections and Diseases

Bacterial Gastrointestinal Infections

  • Dental Caries: Streptococcus mutans is a frequent cause.
  • Periodontal Disease: Gums are swollen, tender, red, or bleeding.
  • Peptic Ulcers: Helicobacter pylori is a causing agent.
  • Shigellosis: Diarrhea with blood and abdominal pain, enterotoxin.
  • Traveler’s Diarrhea: Caused by E. coli, common in developing countries.
  • Campylobacter Diarrhea: Diarrhea that chickens are the main source of infection.
  • Clostridium difficile: Pseudomembranous colitis in severe cases.
  • Salmonellosis: Is often acquired by consuming contaminated eggs.
  • Typhoid Fever: Acquired by contaminated food or water.
  • Cholera: Diagnosis of “rice-water” stool.
  • Food Poisoning: Nausea, vomiting, diarrhea caused by S. aureus.

Viral Gastrointestinal Infections

  • Oral Herpes: Presence of cold sores caused by HHV-1.
  • Mumps: Once common in childhood and humans are the only host.
  • Viral Gastroenteritis: One common pathogen is Rotaviruses.
  • Viral Hepatitis: Jaundice, abdominal pain, vomiting, and weight loss.

Parasitic Gastrointestinal Infections

  • Giardiasis: Individuals ingest cysts from contaminated water.
  • Cryptosporidiosis: Severe watery diarrhea with serious complications.
  • Amebiasis: Severe diarrhea, colitis, caused by Entamoeba histolytica.
  • Tapeworm: Taenia saginata and Taenia solium in beef and pork.
  • Pinworm: Enterobius vermicularis, symptom – perianal itching.
  • Anisakiasis: Prevented by avoiding raw and undercooked marine fish.

Accessory Digestive Organs

  • Tongue and teeth
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas