ch 14 ppt

Pathology, Infection, and Disease

• Pathology: The study of disease. This field encompasses various areas:
  • Etiology: The cause of disease.
  • Pathogenesis: The manner in which a disease develops.
  • Effect of Disease: The impact of disease on the body.
• Infection vs Disease:
  • Infection: The presence of a pathogenic microbe in the body.
  • Disease: Occurs when tissue damage results from infection.

Normal Microbiota and the Host

• At birth, infants become colonized by microorganisms.
• Colonization occurs in several body areas, notably:
  • Lower intestine
  • Upper respiratory tract
• Normal Flora:
  • Permanent residents: Always present, generally non-pathogenic.
  • Transient flora: Temporarily present.
• Symbiosis: Interactions between normal microbiota and the host.
  • Types of symbiosis include:
  • Commensalism: One benefits without affecting the other (e.g., Staphylococcus epidermidis).
  • Mutualism: Both benefit (e.g., E. coli producing vitamins in intestines).
  • Parasitism: One benefits at the other's expense (e.g., pathogens).

Opportunistic Microorganisms

• Pathogens that only cause disease under favorable conditions.
• Example: Staphylococcus aureus causing toxic shock syndrome.

Normal Flora Interactions

• Synergism: Combined effects of organisms that enhance the outcome (e.g., Trichomonas vaginalis increasing susceptibility to HIV).
• Cooperative interactions in microbial communities.

Classifying Infectious Diseases

• Symptoms: Subjective changes felt by patients (e.g., pain).
• Signs: Objective changes that can be measured (e.g., fever).
• Syndrome: A group of signs and symptoms associated with a specific disease.
• Types of Diseases:
  • Communicable: Spread from host to host (e.g., influenza).
  • Noncommunicable: Not transmitted between hosts (e.g., tetanus).

Occurrence of a Disease

• Incidence: Fraction of the population contracting a disease during a time period.
• Prevalence: Fraction of a population with a specific condition at a time.
• Disease classifications include:
  • Sporadic Disease: Rare occurrences.
  • Endemic Disease: Constant presence (e.g., Neisseria gonorrhoeae).
  • Epidemic Disease: Rapid increase in incidence across a region.
  • Pandemic Disease: Worldwide spread (e.g., COVID-19).

Severity or Duration of a Disease

• Acute Disease: Rapid onset and short duration (e.g., flu).
• Chronic Disease: Develops slowly and lasts long (e.g., TB).
• Asymptomatic Disease: No noticeable symptoms; person may be a carrier.
• Latent Disease: Inactive period where symptoms are absent (e.g., shingles).

Extent of Host Involvement

• Local Infection: Limited to a small body area (e.g., a boil).
• Systemic Infection: Throughout the body (e.g., chicken pox).
• Focal Infection: Multiple but defined areas impacted (e.g., tuberculosis).
• Sepsis/Septicemia: Infection and inflammation due to microbes in the blood.

Stages of Disease Development

• Incubation Period: Time between infection and symptom onset.
• Prodromal Period: Mild symptoms appear after incubation.
• Invasive Phase (Illness): Major symptoms evident, possibly fulminating infection.
• Period of Decline: Symptoms lessen, increased risk of secondary infection.
• Convalescent Period: Recovery and strong immune response, though at risk of secondary infection.

Spread of Infection

• Infectious Agent Sources: Need a source to maintain infectivity, often found in hosts.
• Entry and Exit Portals:
  • Entrances: Mucous membranes (respiratory, GI, urinal), skin, parenteral routes.
  • Exits: Respiratory, GI, and genitourinary tracts, skin, blood.

Reservoirs of Infection

• Reservoir: Continuous source of pathogens, which can be living (human/animal) or nonliving (water, soil).

Transmission of Disease

• Methods of Transmission:
  • Contact: Direct (close association) or indirect (via fomites).
  • Droplet: Via airborne droplets.
  • Vehicle: Inanimate reservoir transmission (e.g., water/food).
  • Vectors: Arthropods transmitting via mechanical or biological means.

Nosocomial Infections

• Infections acquired in healthcare settings, affecting 5-15% of patients.
• Common types include MRSA, CRE, and C-DIF.
• Involves patient-to-patient spread, and requires strict infection controls.

Emerging Infectious Diseases

• New or increasing diseases influenced by:
  • Genetic changes
  • Antibiotic misuse
  • Climate change
  • Human expansion and transportation.

Epidemiology

• Study of disease occurrence and transmission patterns.
• Key metrics:
  • Morbidity: Disease incidence.
  • Mortality: Disease-related deaths.

Historical Figures in Epidemiology

• John Snow: Mapped cholera occurrence in London, demonstrated the water pump's role in transmission.
• Ignaz Semmelweis: Advocated handwashing to decrease infection rates.
• Florence Nightingale: Improved sanitation practices affecting health.

Cholera and Its Outbreaks

• Caused by Vibrio cholerae, transmitted through contaminated water.
• Severe dehydration can occur, leading to high mortality without treatment.
• Historical outbreaks highlight sanitation's critical role in disease control (e.g., Goma Refuge Camp, 1994).
• Cholera leads to characteristic "rice water" stool in patients.

The Broad Street Pump Incident

• John Snow's intervention in 1854 involving the pump handle removed due to contamination concerns.
• The true cause was later traced to a cesspit leaking into the water source, illustrating the importance of sanitary practices.