Ch.16+Disease+and+Epidemiology

Chapter 16: Disease and Epidemiology

Pathology, Infection, & Disease

  • Pathology: Study of disease

  • Etiology: Cause of a disease

  • Pathogenesis: Development of disease

  • Infection: Invasion/colonization of the body by pathogens

    • Infection can exist without detectable disease.

    • Abnormal presence of microorganisms causes infection.

  • Disease: Abnormal state in which the body does not perform normal functions.

Human Microbiome

  • Microbial establishment: Begins before birth, during in utero.

    • Placental microbiome: Limited bacteria, mainly Enterobacteriaceae and Propionibacterium.

    • Vaginal delivery introduces Lactobacilli into the newborn's intestines.

    • Rapid changes occur in the microbiome during the first three years of life.

Birth, Microbiome, & Health Conditions

  • Vaginal Birth:

    • Microbiome rich in Lactobacillus and Bacteroides.

  • Cesarean Birth:

    • Microbiome is similar to skin, notable presence of Staphylococcus aureus.

Human Microbiome Analysis

  • Human Microbiome Project: Investigates relationships between microbial communities and health.

  • Normal microbiota: Permanently colonize the host and generally do not cause disease under normal conditions.

  • Transient microbiota: Present for limited durations (days, weeks, or months).

Distribution and Composition

  • Determined by various factors:

    • Nutrients

    • Physical and chemical factors

    • Host defenses

    • Mechanical factors

Representative Normal Microbiota

  • Skin:

    • Microbes include Propionibacterium, Staphylococcus, and others.

    • Antimicrobial properties of secretions prevent resident establishment.

  • Eyes (Conjunctiva):

    • Similar microbiota as skin, influenced by tears and blinking.

  • Nose and Throat:

    • Despite potential pathogens, microbial antagonism reduces disease risk.

  • Mouth:

    • Abundant moisture and nutrients support diverse microbe populations.

  • Large Intestine:

    • Largest population of microbiota due to moisture and nutrients available.

  • Urinary and Reproductive Systems:

    • Vagina has acid-tolerant microbes; urine flow and mucus prevent attachment.

Influencing Factors on Microbiota

  • Factors include:

    • Age

    • Nutritional status

    • Health status

    • Stress

    • Living conditions

    • Lifestyle

Relationships Between Microbiota and Host

  • Microbial antagonism: Competition between microbes protects the host.

    • Mechanisms:

      • Nutrient competition

      • Production of harmful substances

      • pH and oxygen availability

Symbiosis Types

  • Commensalism: One benefits; the other is unaffected.

  • Mutualism: Both benefit.

  • Parasitism: One benefits at the other’s expense.

  • Some normal microbiota are opportunistic pathogens, causing disease in different environments.

Koch’s Postulates

  • Developed by Robert Koch to determine disease causation:

    1. Same pathogen present in every disease case.

    2. Pathogen must be isolated and grown in pure culture.

    3. Pathogen should cause disease when inoculated into a healthy host.

    4. Pathogen must be isolated from the inoculated host.

  • These postulates aid in diagnosing and treating diseases.

Exceptions to Koch’s Postulates

  • Modified for viruses/bacteria that cannot be cultured.

  • Some diseases have varied causative agents (e.g., pneumonia).

Classifying Infectious Diseases

  • Symptoms: Subjective changes felt by patient (not visible).

  • Signs: Objective changes visible & measurable.

  • Syndrome: Specific group of signs/symptoms for a disease.

  • Communicable diseases: Spread between hosts.

  • Contagious diseases: Easily spread.

  • Noncommunicable diseases: Not spreadable (e.g., tetanus).

Epidemiology Overview

  • Epidemiology: Study of disease occurrence and transmission in populations.

  • Incidence: New cases during a time period.

  • Prevalence: Total cases at a specified time.

Disease Occurrence Types

  • Sporadic disease: Occasional occurrences.

  • Endemic disease: Constant presence in population.

  • Epidemic disease: Affecting many individuals in a short time.

  • Pandemic disease: Worldwide spread.

Disease Severity and Duration

  • Acute disease: Rapid symptom onset; short duration (ex: influenza).

  • Chronic disease: Slow symptom development; prolonged duration (ex: Hep. C).

  • Latent disease: Inactive but can later produce symptoms (ex: shingles).

Herd Immunity

  • Immunity in the majority of the population reduces spread of disease.

Types of Infections

  • Local infection: Limited to a small area.

  • Systemic infection: Widespread throughout the body.

  • Focal infection: Local infection that spreads systemically.

Sepsis and Related Conditions

  • Sepsis: Toxic condition due to microbe spread.

  • Bacteremia: Bacteria in blood.

  • Viremia: Viruses in blood.

  • Toxemia: Toxins in blood.

Patterns of Disease

  • Infection and disease have a sequence:

    • Reservoir of infection → Transmission → Invasion → Pathogenesis.

Predisposing Factors

  • Factors influencing disease occurrence:

    • Gender, age, climate, health status, lifestyle.

Stages of Disease Development

  1. Incubation period: Time from infection to first symptoms.

  2. Prodromal period: Early mild symptoms.

  3. Period of illness: Severe disease manifestation.

  4. Period of decline: Symptoms subside.

  5. Period of convalescence: Return to prediseased state.

Reservoirs of Infection

  • Human reservoirs: Carriers can be asymptomatic or latent.

  • Animal reservoirs: Transference of zoonoses.

  • Nonliving reservoirs: Situations like soil and water.

Contact Transmission

  • Direct contact: Close association needed.

  • Indirect contact: Via fomite (nonliving object).

  • Droplet transmission: Airborne droplets less than 1 meter.

Vehicle Transmission

  • Involves inanimate reservoirs:

    • Airborne

    • Waterborne

    • Foodborne

Vectors of Disease

  • Arthropods: Fleas, ticks, and mosquitoes transmit diseases.

    • Mechanical transmission: Pathogen on vector's feet.

    • Biological transmission: Pathogen reproduces in the vector.

Healthcare-Associated Infections (HAIs)

  • Infections acquired during healthcare treatment.

  • Affect 1 in 25 hospital patients; result in 70,000 deaths annually.

Control of Healthcare-Associated Infections

  • Standard precautions: Basic hygiene measures.

  • Transmission-based precautions: For known/suspected infections.

  • Efforts include handwashing and thorough cleaning to minimize infection risks.

Epidemiology and CDC Responsibilities

  • Epidemiology: Studies disease patterns and suggests control methods.

  • CDC: Collects/analyzes epidemiological data in the U.S.; publishes reports on disease morbidity and mortality.