NURS 236: Human-Microbe Interactions Quiz

Human-Microbe Interactions: Principles of Disease and Transmission

• This course, NURS 236, focuses on human-microbe interactions and disease transmission.
• Learning objectives include recalling predisposing factors for disease, explaining disease stages, exploring infection reservoirs, contrasting transmission methods, and providing examples.

Patterns of Disease

• Predisposing Factors: Any factor that increases a host's susceptibility to infection or alters disease progression.
  • Examples include gender (UTIs, pneumonia), genetics (sickle-cell anemia, malaria), climate (MO survival), environment, lifestyle, and occupation.
• Stages of Disease:
  • Incubation period: Initial infection to first symptoms, early, mild symptoms; might be absent in some diseases.
  • Prodromal period: Early, mild symptoms; relatively short; may not be present in all diseases (due to virulence).
  • Period of illness: Most severe signs and symptoms; major immune response occurs.
  • Period of decline: Symptoms decrease, susceptibility to secondary infections increases.
  • Period of convalescence: Return to normal/homeostasis. -Stages can link to stages of microbial growth. Different microbes may have varying periods for each phase.

Spread of Infection: Reservoirs

• Reservoirs: Source of disease-causing microbes.
• 3 major groups:
  • Humans:
    • Symptomatic individuals.
    • Asymptomatic individuals (e.g., carriers like hospital staff with MRSA).
    • During incubation/convalescence stages of disease (e.g., STIs, streptococcal infections).
  • Animals:
    • Zoonoses: Diseases transferred from animals to humans.
    • Spread through many routes (direct contact with animal/feces, contaminated water/food/products/hides).
    • Can be transmitted by arthropods (insect vectors).
  • Nonliving:
    • Environmental sources of infection.
    • Soil: Fungi, nematodes, Clostridium tetani, C. botulinum.
    • Water: Protozoa, some helminths.
    • Food: Food poisoning (e.g., salmonellosis).

Spread of Infection: Transmission

• 3 Modes: Contact, vehicles, vectors.
• Contact:
  • Direct Contact: Physical contact (touching, kissing) between sources and hosts. Common cold, influenza, Hepatitis A, measles, STIs. Prevention via protective equipment.
  • Indirect Contact: Physical contact through nonliving objects (e.g., HIV or hepatitis B in contaminated syringes, organisms living in a hospital environment). Prevention by maintaining a clean environment.
  • Droplet: Contact with aerosolized liquid containing microbes (<1 m). Influenza, whooping cough. Prevention via good hygiene.
• Vehicle Transmission: Diseases transmitted by a medium.
  • Water: Fecal contamination (cholera, leptospirosis)
  • Food: Poor cooking/storage (food poisoning, tapeworms).
  • Air: Similar to droplet (larger distances); airborne microbes/dust (tuberculosis, fungal infections).
• Vectors: Microbes transmitted between hosts by another organism (typically an insect).
  • Mechanical: Passive transport by insect from vector's body to food (typhoid fever).
  • Biological: More active and complex; some phase of microbial life cycle occurs in a vector (malaria by Plasmodium species).

Nosocomial Infections

• Infections acquired during a hospital or other healthcare-associated visit.
• Increasing frequency.
• Interaction between 3 factors (microorganisms in the hospital environment, compromised host, chain of transmission).
  • Microorganisms: Common in hospital environment. Resistance to cleaning agents and antibiotics.
  • Compromised Host: Many body structures prevent illness; these structures can be broken (open wounds, skin), or the immune system can be weakened.
  • Chain of Transmission: Mostly through direct and indirect contact between hospital staff and patients, or between patients, or shared equipment.

Emerging Infectious Diseases

• Diseases that either appear for the first time or change in a manner that increases incidence.
• Factors Influencing Emergence:
  • New Diseases: (e.g., HIV). Zoonotic diseases that newly infect humans (e.g., West Nile virus, smallpox).
  • Genetic: Acquisition of new traits (e.g., antibiotic resistance, toxin production).
  • Environmental: Movement of microbes, reservoirs, or vectors to new areas, climate change altering disease patterns.

Important terms

• Pathology: Scientific study of disease.
• Etiology: Cause of a particular disease, often a specific microorganism.
• Pathogenesis: Steps in the progression of a disease.
• Infection: Pathogenic microorganism enters a host and begins to grow.
• Disease: Change in a host's state of health associated with infection.

Many MOs on the human body

• Microbiomes impacted by many factors.
• Differences between Normal and Transient Microbiota:
  • Normal: Normally found on the body.
  • Transient: Live on/in the body for a period of time and then leave.
  • Differences exist among individuals.

Example Human-Microbe Relationships

• Relationships: Commensalism (one benefits, other unaffected); mutualism (both benefit); parasitism (one benefits at expense of other) are affected by conditions and potentially by opportunistic pathogens like Candida albicans and Clostridium difficile.