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• Pathogens


  Disease-causing microorganisms
• Pathogenic microorganisms


  • Have special properties that allow them to invade the human body or produce toxins
• When a microorganism overcomes the body's defenses


  A state of disease results
• Pathology


  The scientific study of disease
• Pathology


  • Concerned with the etiology (cause), pathogenesis (development), and effects of disease
• Infection


  The invasion and growth of pathogens in the body
• Host


  An organism that shelters and supports the growth of pathogens
• Disease


  An abnormal state in which part or all of the body is not properly adjusted or is incapable of performing normal functions
• Microorganism colonization


  Microorganisms begin colonization in and on the surface of the body soon after birth
• Normal microbiota


  Microorganisms that establish permanent colonies inside or on the body without producing disease
• Transient microbiota


  Microbes that are present for various periods and then disappear
• Normal microbiota can prevent pathogens from causing an infection


  This phenomenon is known as microbial antagonism
• Symbiosis


  The normal microbiota and the host living together
• Types of symbiosis


  • Commensalism (one organism benefits, and the other is unaffected)
  • Mutualism (both organisms benefit)
  • Parasitism (one organism benefits, and one is harmed)
• Opportunistic pathogens


  Do not cause disease under normal conditions but cause disease under special conditions
• Koch's postulates


  Criteria for establishing that specific microbes cause specific diseases
• Koch's postulates requirements


  • The same pathogen must be present in every case of the disease
  • The pathogen must be isolated in pure culture
  • The pathogen isolated from pure culture must cause the same disease in a healthy, susceptible laboratory animal
  • The pathogen must be reisolated from the inoculated laboratory animal
• Koch's postulates are modified to establish etiologies of diseases caused by viruses and some bacteria, which cannot be grown on artificial media
• Some diseases, such as tetanus, have unequivocal signs and symptoms
• Some diseases, such as pneumonia and nephritis, may be caused by a variety of microbes
• Some pathogens, such as S. pyogenes, cause several different diseases
• Certain pathogens, such as HIV, cause disease in humans only
• Symptoms


  Subjective changes in body functions
• Signs


  Measurable changes
• Diagnosis


  Identification of the disease
• Syndrome


  A specific group of symptoms or signs that always accompanies a specific disease
• Communicable diseases


  Transmitted directly or indirectly from one host to another
• Contagious disease


  A very communicable disease that is capable of spreading easily and rapidly from one person to another
• Noncommunicable diseases


  Caused by microorganisms that normally grow outside the human body and are not transmitted from one host to another
• Incidence


  Number of people contracting the disease
• Prevalence


  Number of people with the disease
• Disease occurrence


  • Sporadic
  • Endemic
  • Epidemic
  • Pandemic
• Scope of a disease

  • Acute
  • Chronic
  • Subacute
  • Latent
• Herd immunity


  The presence of immunity to a disease in most of the population
• Local infection


  Affects a small area of the body
• Systemic infection


  Spread throughout the body via the circulatory system
• Primary infection


  An acute infection that causes the initial illness
• Secondary infection


  Can occur after the host is weakened from a primary infection
• Subclinical infection


  Does not cause any signs or symptoms of disease in the host
• Predisposing factor


  One that makes the body more susceptible to disease or alters the course of a disease