Session 10

• Pathology


  The study of disease
• Etiology


  The study of the cause of a disease
• Pathogenesis


  The development of disease
• Pathogen


  Have special properties that allow them to invade the human body or produce toxins
• Infection

  Colonization of the body by pathogens
• Disease


  An abnormal state in which the body is not functioning normally
• Normal Microbiota (Flora)


  • Microbial Antagonism due to competition between microbes
  • Resident Flora (normal) acquired at passage through birth canal

  
• Resident Flora (normal)


  • Establish permanent colonies on/inside body without producing disease
  • Protect the host by occupying niches that pathogens might occupy (Competitive exclusion)
  • Protect the host by producing acids
  • Protect the host by producing bacteriocins
  • Protect the host by stimulation of immune system
• Protective role of Resident Flora

  • Prevent pathogens from attaching
  • Consume available nutrients
  • Produce toxic compounds that inhibit other microbes
• Transient Microbiota (Flora)


  Certain microbes are present for various periods (days, weeks, or months) – then disappears
• Probiotics


  Live microbes applied to or ingested into the body, intended to exert a beneficial effect
• Dynamic nature of resident flora: changes due to age, type of food consumed, Hormonal state, antibiotics
• Various Co-existence Relationships Between Bacteria and Host

  • Symbiosis
  • Mutualism
  • Commensalism
  • Parasitism
• Opportunistic pathogens


  Cause disease under special conditions (mutualistic relationship becomes parasitic)
• Healthy carriers of pathogenic organisms
• Cooperation among microorganisms: One microorganism may make it possible for another to cause disease or produce more severe symptoms
• Koch's Postulates: Proof of Etiology of Infectious Diseases


  • The same pathogen must be present in every case of the disease
  • The pathogen must be isolated from the diseased host and grown in pure culture
  • The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible lab animal
  • The pathogen must be isolated from the inoculated animal and must be shown to be the original microbe
• Exceptions to Koch's Postulates


  • To establish disease etiology for viruses and bacteria, which cannot be grown on artificial media
  • Some diseases, e.g.: 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
• Symptom


  A change in body function that is felt by a patient as a result of disease
• Sign


  A change in a body that can be measured or observed as a result of disease
• Syndrome


  A specific group of signs and symptoms that accompany a disease
• Communicable vs. Non-communicable vs. Contagious

  • Communicable disease: A disease that is spread from one host to another
  • Contagious disease: A disease that is easily spread from one host to another
  • Noncommunicable disease: A disease that is not transmitted from one host to another
• Incidence


  Fraction of a population that contracts a disease during a specific time
• Prevalence


  Fraction of a population having a specific disease at a given time
• Occurrence of a Disease


  • Sporadic disease: Disease that occurs occasionally in a population
  • Endemic disease: Disease constantly present in a population
  • Epidemic disease: Disease acquired by many hosts in a given area in a short time
  • Pandemic disease: Worldwide epidemic
• Severity or Duration of a Disease


  • Acute: Disease develops rapidly
  • Chronic: Disease develops slowly
  • Subacute: Symptoms between acute and chronic
  • Latent: Disease with a period of no symptoms when the causative agent is inactive
• Herd immunity


  Presence of immunity to a disease in most of the population
• Extent of Host Involvement


  • Toxemia: Toxins in the blood
  • Viremia: Viruses in the blood
  • Primary infection: Acute infection that causes the initial illness
  • Secondary infection: Opportunistic infection after a primary (predisposing) infection
  • Subclinical disease: No noticeable signs or symptoms (inapparent infection)
• Types of Infection


  • Local: limited to small area of body
  • Systemic: spread throughout body via_
  • Focal: spread from local infection to specific areas
  • Primary: acute infection causing initial illness
  • Secondary: occurs after host is weakened from primary infection
  • Subclinical (inapparent): no noticeable signs and symptoms
• Patterns of Disease: Predisposing Factors

  • Genetics
  • Gender
  • Climate and weather
  • Age
  • Stress and fatigue,
  • Lifestyle
  • Chemotherapy
• Coronaviruses are a large family of viruses, some of which can infect people

  
• Mild illness (common colds) and severe, or even fatal, disease - such as Middle East Respiratory Syndrome Coronavirus (MERS-CoV) and SARS
• The natural reservoir for coronaviruses is thought to be animal hosts
• New strains emerge from this reservoir, infect an 'intermediate' host, and from there infect people
• Some coronaviruses are efficient at human-to-human transmission, while others are not

  
• Coronaviruses are common in many different species of animals, including camels, cattle, cats, and bats

  
• The 2019-novel coronavirus (2019-nCoV) is a previously-unidentified strain of coronavirus

  
• Symptoms of 2019-nCoV

  • fever
  • cough
  • shortness of breath
  • difficulty breathing
• 2019-nCoV is capable of causing severe illness, and some infected people have died
• It is possible that people with underlying health conditions are at higher risk for severe disease