CHAPTERS 3&4

• Pathology


  The scientific study of disease
• Etiology


  Cause of disease
• Pathogenesis


  Studies how the disease develops
• Infection


  Invasion or colonization of the body by pathogenic organisms
• Disease


  Occurs when an infection results in a change in a state of health
• Normal Microbiota


  Microbial populations that rapidly establish themselves in the newborn's body after birth
• Resident Microbiota


  Microorganisms that remain throughout an individual's life
• Transient Microbiota


  Microorganisms that are present for a certain time period and then disappear
• Microbial Antagonism


  • Normal flora inhibits the overgrowth of harmful microbes through competition for nutrients and affecting environmental factors such as pH, toxic substances, and oxygen availability
• Symbiosis Relationship


  • Commensalism - One organism benefits, and the other is not affected (+/0)
  • Mutualism - Both organisms benefit from living together (+/+)
  • Parasitism - One organism benefits benefits, and the other is harmed (+/-)
• Opportunistic Pathogens


  Organisms that normally do not cause disease in their natural habitat in a healthy person, but may cause disease if the host is weakened or if they enter a different part of the body
• Synergism


  The effect of two microbes acting together is greater than the effect of either acting alone
• Etiology of Infectious Disease

  Diseases can be caused by many factors: infection, genetics, degeneration, and others
• Symptoms


  Subjective feelings that are not obvious to an observer, e.g. pain and malaise
• Signs


  Objective changes that can be measured, e.g. fever, redness, swelling, paralysis

  
• Syndrome


  A group of signs and symptoms that are associated with a disease, e.g. AIDS (Acquired Immune Deficiency Syndrome)
• Types of Infectious Diseases

  • Communicable Diseases - Spread from one host to another, directly or indirectly
  • Contagious Diseases - Spread easily from one person to another
  • Noncommunicable Diseases - The disease is not spread from one host to another
• Disease Incidence


  Percentage of the population that contracts a disease in a given time period
• Disease Prevalence


  Percentage of the population that has the disease during the given time period
• Types of Disease Occurrence

  • Sporadic Disease - Occurs only occasionally
  • Endemic Disease - Constantly present in the population
  • Epidemic Disease - Many people acquire the disease in a short time period
  • Pandemic Disease - Worldwide epidemic
• Types of Disease Duration

  • Acute Disease - Develops rapidly, but lasts a short time
  • Chronic Disease - Develops more slowly, and reactions are less severe. Tend to recur for long periods or to be continual
  • Subacute Disease - Intermediate between acute and chronic
  • Latent Disease - Causative agent remains inactive for a time, but then becomes active and produces disease symptoms

  
• Types of Host Involvement

  • Local Infection - Microorganism is limited to a small part of the body
  • Systemic Infection - Microbes are spread throughout the body by blood or lymph
  • Focal Infection - Starts as a local infection and spreads to other parts of the body

  
• Types of Host Resistance

  • Primary Infection - Acute infection that causes initial illness
  • Secondary Infection - Caused by opportunistic pathogen after primary infection has weakened the host immune system
  • Subclinical Infection - Does not cause any noticeable illness in the host
• Reservoirs of Infection

  • Human Reservoir - Infected individuals who may or may not present disease
  • Animal Reservoir - Zoonoses are diseases that occur primarily in wild and domestic animals
• Types of Disease Transmission

  • Contact Transmission - Direct, indirect, or droplet
  • Vehicle Transmission - Waterborne or airborne
  • Vector Transmission - Mechanical or biological
• Nosocomial Infections


  Infections acquired in a healthcare setting, often due to a wide variety of microbes, weakened or immunocompromised patients, and transmission via healthcare workers, patients, fomites, or airborne
• Important Nosocomial Pathogens

  • Normal microbiota
  • Antibiotic-resistant bacteria, especially Gram-negative Enterobacteria like E. coli, Klebsiella, Proteus, Enterobacter, and Serratia

  
• Stages of Disease Development

  • Incubation Period
  • Prodromal Period
  • Illness Period
  • Decline Period
  • Convalescence Period

  
• Epidemiology


  The science that studies when and where diseases occur and how they are transmitted in a population
• Types of Epidemiological Investigation

  • Descriptive Epidemiology - Retrospective studies that collect data on disease occurrence
  • Analytical Epidemiology - Analyze a disease to determine its probable cause
  • Experimental Epidemiology - Test drugs or vaccines on susceptible populations
• Carrier


  A person or animal with an asymptomatic infection that can be transmitted to another susceptible person or animal
• Microbiota


  Microbial flora harbored by normal, healthy individuals
• Nonpathogen


  A microorganism that does not cause disease; it may be part of the normal microbiota
• Opportunistic Pathogen


  An agent capable of causing disease only when the host's resistance is impaired (i.e., when the patient is immunocompromised)
• Pathogen


  A microorganism capable of causing disease
• Pathogenicity


  The ability of an infectious agent to cause disease
• Virulence


  The quantitative ability of an agent to cause disease. Virulent agents cause disease when introduced into the host in small numbers.
• Adherence


  The process by which bacteria stick to the surfaces of host cells. A major initial step in the infection process.

  
• Invasion


  The process whereby microbes enter host cells or tissues and spread in the body
• Toxigenicity


  The ability of a microorganism to produce a toxin that contributes to the development of disease