infection
Immune Response to Injury
Injury Activation System: When skin injury occurs, a signaling system activates to initiate the immune response.
Vasodilation: Blood vessels expand, increasing blood flow to the injury site, which aids healing by delivering immune cells and nutrients.
Increased Fluid: Fluid accumulation helps to clear pathogens and debris.
Role of Immune Cells
Migration of Immune Cells: Upon arrival at the injury site, immune cells aim to seal the wound and clear out debris.
Pathogen Destruction: Immune cells work to eliminate any microorganisms present to prevent infection.
Consequences of Failure: If immune response is insufficient and microorganisms are not contained, it can lead to infection and potential organ destruction.
Lines of Defense Against Microorganisms
Microorganisms and Resident Flora: The body hosts a balance of beneficial and harmful microorganisms known as resident flora.
Commensal Relationship: Healthy resident flora usually coexist without causing harm (e.g., h. pylori in the stomach).
Potential Imbalances: If resident flora overgrows, it can lead to problems (e.g., h. pylori causing ulcers).
Importance of Balance: A diverse microbiome is healthy and necessary; disruption can lead to disease.
Pathogens and Disease Mechanisms
Definition of Pathogen: A microbe capable of causing disease.
Mechanisms of Damage: Pathogens may destroy host cells, interfere with their function, or produce toxins that harm cells.
Important Terms in Infection Dynamics
Pathogenicity: The capacity of a microbe to cause disease.
Virulence: The degree of pathogenicity; how effective a pathogen is at causing disease.
Toxigenicity: Ability of a pathogen to produce toxins.
Antigenicity: The ability of a microbe to be recognized by the immune system.
Co-infection vs Superinfection:
Co-infection: Two pathogens causing disease simultaneously.
Superinfection: New infection occurring in a patient already suffering from an existing infection.
Types of Pathogens
Parasites: Categorized as obligate (needs host) and facultative (can live independently).
Helminths: Worms that can cause disease but exposure might also provide beneficial effects (e.g., helminth therapy in autoimmunity).
Bacteria: Common single-celled organisms.
Classification: Identified by shape (rod, circular) and staining properties (gram-positive, gram-negative).
Inducing Inflammation: Bacteria can provoke an immune response and produce toxins.
Endotoxins & Exotoxins:
Endotoxins: Released from gram-negative bacteria when they lyse (e.g., LPS causing septic shock).
Exotoxins: Secreted by living bacteria and target various body functions.
Viruses: Obligate parasites that replicate using host cell machinery, leading to acute or chronic infections.
Reactivation of Dormant Viruses: E.g., shingles due to chickenpox reactivation in immunocompromised individuals.
Fungi: Larger organisms that thrive in warm, moist environments (e.g., yeast infections).
Protozoa: Larger parasites (e.g., trichomonas).
Chain of Infection
Concept: Series of steps necessary for a pathogen to successfully infect a host.
Essential Steps:
Infectious Agent: Virus, bacteria, etc.
Reservoir: Where pathogens live before transmission.
Portal of Exit: Route by which the pathogen leaves the reservoir.
Mode of Transmission: How the pathogen moves to another host.
Portal of Entry: Route into a new host.
Susceptible Host: Individual who can be infected.
Breaking Chains to Prevent Infection: Interfering with any step can halt infection spread.
Phases of Infection
Exposure: Initial contact with a pathogen starts the infection process.
Incubation Phase: Pathogen multiplies without causing symptoms.
Prodrome Phase: Non-specific symptoms indicating an infection is present.
Clinical Illness: Specific symptoms emerge related to the infection.
Recovery/Chronic Infection: Immune system either resolves the infection or the individual experiences ongoing illness.
Clinical Manifestations of Infection
Local: Specific to the site of infection (e.g., inflammation).
Systemic: Affects the entire body (e.g., fever, weakness).
Diagnostic Measures: White blood cell count indicates infection severity (e.g., leukocytosis). Presence of antibodies and cultures assists in identifying pathogens and proper treatment.
Match Treatment to Pathogen: Antibacterial for bacterial infections, antiviral for viral, and antifungal for fungal infections.
Influenza
Definition: Viral infection affecting the epithelial cells of the airway.
Caused by different strains: Types A, B, and C.
Rapid mutation leads to different subtypes annually, complicating vaccination.
Transmission: Primarily through respiratory droplets.
Pathophysiology:
Attaches to epithelial cells, inhibiting mucus production and ciliary movement.
Causes necrosis in infected cells, leading to shedding and symptom presentation.
Impairs oxygen exchange which can result in complications such as bacterial pneumonia.
Clinical Manifestations:
Common symptoms include cough, fever, and systemic symptoms.
Diagnosis:
Based on patient history, symptoms, and viral tests for types A & B.
Treatment:
Focus on prevention with handwashing and flu vaccines.
Antiviral medications available but no antibiotics needed for viral infections.
Hepatitis
Definition: Inflammatory process of the liver, focusing here on viral causes.
Can be acute or chronic and transmitted via fecal-oral routes or bodily fluids.
Role of the Liver: Produces bile, detoxifies substances, and is crucial for overall health.
Pathophysiology:
Viral entry leads to necrosis of hepatocytes.
Types of Hepatitis Viruses: A, B, C (vaccines available for A and B).
Clinical Manifestations:
Symptoms include fatigue, jaundice (icterus), hepatomegaly, clay-colored stools, and dark urine.
Diagnosis:
Blood tests for antibodies, elevated bilirubin levels, and clotting time assessments.
Treatment:
Emphasis on hygiene, vaccination, and symptom management. Antivirals may be prescribed.
Tuberculosis (TB)
Definition: A highly contagious bacterial infection caused by Mycobacterium tuberculosis.
Transmitted via airborne droplets; humans are the sole reservoir.
Pathophysiology:
Infiltrates lungs, eliciting an immune response that contains the bacteria in granulomas.
Clinical Manifestations:
Common signs include fatigue, weight loss, night sweats, and productive cough (hemoptysis).
Diagnosis:
Gold standard test: QuantiFERON Gold. Additional tests include sputum cultures, NAT tests, and chest X-rays.
Treatment:
Requires long-term antibiotic therapy and monitoring.
Preventive measures include vaccinations and protective gear (N95 masks for caregivers, surgical masks for the patient).
Urinary Tract Infections (UTIs)
Definition: Infection of the urinary tract, typically caused by E. coli
Pathophysiology:
Bacteria ascend from the rectum to the urinary tract, leading to tissue necrosis.
Clinical Manifestations:
Symptoms include dysuria (painful urination), frequency, urgency, and possible hematuria (blood in urine).
Diagnosis:
Urinalysis and urine cultures to identify pathogens. Presence of nitrites indicates infection.
Treatment:
Administering antibiotics and increasing fluid intake to flush bacteria.
Educating on hygiene practices, especially for women (wiping front to back).
Meningitis
Definition: Infection of the meninges, commonly caused by bacteria.
Spread through respiratory droplets; rapid onset of severe symptoms.
Pathophysiology:
Bacterial growth leads to inflammation of meninges, which can affect brain function.
Clinical Manifestations:
Key symptoms: sudden severe headache, nuchal rigidity, altered mental status, and seizures.
Diagnosis:
Analysis of cerebrospinal fluid (CSF) through spinal tap alongside blood work.
Treatment:
Requires immediate initiation of antibiotics and may involve vaccination of close contacts.