Prions are misfolded proteins capable of inducing abnormal folding of normal proteins in the brain, leading to neurodegenerative diseases.

• Examples of prion diseases:

  • Creutzfeldt-Jakob disease (CJD)

  • Bovine spongiform encephalopathy (mad cow disease)

• Mechanism of Infection: Unlike other pathogens, prions do not replicate but induce the conversion of normal proteins into abnormal forms.

II. Sources of Infection

The source or reservoir of infection is the habitat where the pathogen normally lives and multiplies. Understanding sources is vital in breaking the chain of infection.

1. Human Reservoirs

Humans can harbor pathogens with or without symptoms.

• Symptomatic carriers: Individuals actively showing signs of disease

• Asymptomatic carriers: Individuals who harbor pathogens but show no symptoms (e.g., Typhoid Mary)

2. Animal Reservoirs

Some infections are zoonotic, originating from animals.

• Examples:

  • Rabies from dogs and bats

  • Plague from rodents

  • Avian flu from birds

3. Environmental Reservoirs

Non-living environments can harbor infectious agents.

• Examples:

  • Soil: Clostridium tetani (tetanus)

  • Water: Vibrio cholerae (cholera)

  • Surfaces and equipment in hospitals: harbor resistant organisms like MRSA

III. Modes of Transmission

Pathogens are transmitted through various mechanisms. Understanding these pathways is essential for nurses to implement effective infection control measures.

1. Contact Transmission

• Direct contact: Physical contact with an infected individual (e.g., touching wounds, body fluids)

• Indirect contact: Contact with contaminated objects (fomites) such as doorknobs, stethoscopes, or medical devices

2. Droplet Transmission

Occurs when respiratory droplets containing pathogens are expelled during coughing, sneezing, or talking and land on the mucosa of another person.

• Diseases: Influenza, COVID-19, pertussis

3. Airborne Transmission

Involves small particles or aerosols that remain suspended in air and are inhaled.

• Diseases: Tuberculosis, measles, varicella (chickenpox)

4. Vector-Borne Transmission

Vectors such as mosquitoes, ticks, or fleas transmit infections through bites or contact.

• Diseases: Malaria (mosquito), Lyme disease (tick), plague (flea)

5. Common Vehicle Transmission

Occurs when a single contaminated source spreads infection to multiple hosts.

• Examples: Contaminated food, water, medications, or intravenous fluids

IV. Risk Factors That Promote Infection

1. Host Susceptibility

A person’s immune system plays a critical role in defense against infection. Certain conditions increase susceptibility:

• Age: Infants and the elderly have weaker immune defenses

• Chronic diseases: Diabetes, cancer, HIV/AIDS

• Nutritional status: Malnutrition weakens immunity

• Medications: Immunosuppressants, chemotherapy, long-term antibiotics

• Stress and fatigue: Reduce immune responses

• Breaks in skin integrity: Wounds, surgery, burns

2. Hospital/Healthcare Environment

Healthcare settings are high-risk areas due to the presence of vulnerable patients and invasive procedures.

• Catheters and IV lines: Breach natural barriers

• Surgical procedures: Increase infection risk

• Healthcare workers: Can act as vectors

• Contaminated equipment: May harbor resistant bacteria

• Poor hand hygiene: Major contributor to HAIs

3. Invasive Medical Devices

• Urinary catheters: Associated with UTIs

• Central lines: Associated with bloodstream infections

• Endotracheal tubes: Linked to ventilator-associated pneumonia

V. Pathogenesis of Infection

Pathogenesis refers to the process by which an infection leads to disease. Several stages characterize this process:

1. Entry of Pathogen

Pathogens enter through specific portals:

• Respiratory tract (e.g., flu)

• Gastrointestinal tract (e.g., cholera)

• Urogenital tract (e.g., gonorrhea)

• Skin or mucosal breaches (e.g., tetanus)

2. Adhesion to Host Cells

Pathogens must adhere to host tissues using pili, fimbriae, or adhesive proteins.

3. Invasion and Multiplication

After attachment, pathogens invade tissues and multiply, often avoiding immune responses.

4. Host Damage

Damage occurs via:

• Toxin production (e.g., botulinum toxin)

• Immune-mediated injury

• Direct tissue invasion

5. Spread of Infection

Infections may remain localized or spread systemically via blood or lymphatic system (sepsis, bacteremia).

VI. Types of Infections Based on Cause or Source

1. Primary vs. Secondary Infection

• Primary infection: The initial infection caused by a pathogen

• Secondary infection: Occurs due to lowered immunity from the primary infection or treatment

2. Opportunistic Infections

Caused by organisms that do not typically cause disease in healthy individuals but infect immunocompromised hosts.

• Examples: Pneumocystis jirovecii pneumonia in HIV patients

3. Nosocomial or Hospital-Acquired Infections (HAIs)

Infections acquired during hospital stay after 48 hours of admission.

• Common sites: Urinary tract, surgical sites, bloodstream, respiratory tract

• Common pathogens: MRSA, VRE, Clostridium difficile

4. Community-Acquired Infections

Infections acquired outside healthcare settings.

VII. Emerging and Re-Emerging Infections

Increased globalization, climate change, and microbial adaptation have led to the emergence of new pathogens and the re-emergence of old ones.

• Emerging infections: SARS, COVID-19, Ebola

• Re-emerging infections: Tuberculosis, measles

Factors contributing to emergence:

• Antibiotic resistance

• Urbanization

• International travel

• Poor sanitation

VIII. Antimicrobial Resistance (AMR)

A critical modern cause of persistent infections is antimicrobial resistance.

• Definition: The ability of microorganisms to resist the effects of drugs

• Common resistant pathogens:

  • Methicillin-resistant Staphylococcus aureus (MRSA)

  • Vancomycin-resistant Enterococci (VRE)

  • Multidrug-resistant TB (MDR-TB)

• Causes:

  • Overuse and misuse of antibiotics

  • Inadequate infection control

  • Poor patient compliance

  • Agricultural use of antibiotics

• Impact:

  • Prolonged hospital stays

  • Increased mortality

  • Higher treatment costs

IX. Role of Nurses in Preventing Infections

Nurses play a pivotal role in preventing and controlling infections:

• Hand hygiene: Most effective infection prevention measure

• Aseptic techniques: During invasive procedures

• Use of PPE: Gloves, masks, gowns to prevent cross-contamination

• Patient education: Promoting hygiene, vaccination, and medication adherence

• Sterilization and disinfection: Of equipment and environment

• Surveillance and reporting: Early identification and containment of outbreaks