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Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
Chapter 14
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Chapter 14


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  • 1. Chapter 14: Principles of Disease and Epidemiology
    • Pathology = study of disease
      • Etiology = cause of disease
      • Pathogenesis = manner in which disease develops
      • Structural and functional changes brought about by the disease
      • Final effects the disease has on the body
  • 2. Chapter 14: Principles of Disease and Epidemiology
    • Infection = invasion or colonization of the body by pathogens
    • Disease – occurs when an infection results in any change from a state of health
      • Abnormal state where the body can’t carry out its normal fxs
    • Normal flora or normal microbiota = microbes that have permanent residence without producing disease
      • Transient microbiota – present temporarily and then disappear ex. Streptococcus in lg intestine
  • 3. Chapter 14: Principles of Disease and Epidemiology
    • Microbial antagonism or competitive exclusion = normal microbes preventing overgrowth of pathogens
      • Ex. E. coli produces bacteriocins (proteins that are lethal to closely related bacteria) in the large intestine which inhibit the growth of pathogenic Salmonella and Shigella
  • 4. Chapter 14: Principles of Disease and Epidemiology
    • Symbiosis = relationship between normal microbiota and the host
      • Commensalism = 1 organism benefits while the other is unaffected ex. Normal microbiota
      • Mutualism = both organisms benefit
        • Ex. E. coli in the lg intestine synthesizes vitamin K, B which provides nutrients for you and your body provides nutrients for E. coli in the lg intestine
      • Parasitism = 1 organism benefits at the expense of the other ex. Giardia lamblia
  • 5. Chapter 14: Principles of Disease and Epidemiology
    • Opportunistic pathogens - do not cause disease in their normal habitat in a healthy person
      • Cause disease if they gain entrance to an area that they don’t usually inhabit
        • E. coli in urinary tract
        • Pneumocystis jiroveci in AIDS px – fungal pathogen causes pneumonia
    • Probiotics = live bacterial cultures ingested for beneficial effects
      • Prebiotics are chemicals to promote their growth
  • 6. Koch’s Postulates
    • Demonstrate that a specific microbe is the cause of a specific disease
      • he worked with Bacillus anthracis to prove his postulates
    • The same pathogen must be present in every case of the disease
    • 2. the pathogen must be isolated from the diseased host and grown in pure culture
  • 7. Koch’s Postulates
    • 3. The pathogen from the pure culture must cause disease when inoculated into a healthy, susceptible laboratory animal
    • 4. The pathogen must be isolated from the inoculated animal and be the same pathogen as the original organism
  • 8. Exceptions to Koch’s Postulates
    • A few organisms can’t be grown in laboratory media ex. Treponema – bacteria
    • Some diseases may be caused by a variety of organisms and the specific etiology is not easy to determine from the symptoms ex. Pneumonia
    • Some pathogens may infect a # of organs or tissues and cause very different diseases or sxs ex. Streptococcus pyogenes causes sore throat, scarlet fever, puerperal fever
  • 9. Classifying infectious diseases
    • Symptoms – felt by px, subjective and can’t be seen by a dr. ex. Pain
    • Signs – objective changes that a dr. can observe and measure ex. Fever
    • Syndrome = specific group of sxs or signs accompanying a particular disease
    • Communicable diseases = spread directly or indirectly from 1 host to another ex. Typhoid fever, TB
      • If it is highly communicable esp. thru direct contact = contagious
  • 10. Classifying infectious diseases
    • Non-communicable diseases = caused by microbes like Clostridium tetani which enters the body through a wound
    • Incidence = the # of new cases of a disease during a particular time period
      • It is an indicator of the spread of the disease
    • Prevalence = total # of cases of a disease (old and new) in a certain area and time period
  • 11. Classifying infectious diseases
    • Sporadic diseases occur only occasionally and in an unpredictable fashion ex. Tetanus
    • Endemic diseases are present constantly at a certain level in a particular location
      • Common cold throughout US
      • Lyme disease endemic to some eastern states
  • 12. Classifying infectious diseases
    • Epidemic a sudden increase in morbidity (illness rate) and mortality (death rate) above the usual for a disease = many people in a given area acquire a certain disease in a short period of time
    • Pandemics = worldwide epidemics
    • Acute disease – develops rapidly but lasts for a short period of time ex. Influenza
      • Primary infection = initial acute infection
      • Secondary infection – caused by opportunist after primary infection weakens body defenses
  • 13. Classifying infectious diseases
    • Chronic disease – develops slowly, often the rx is less severe, is continuous or recurrent for long periods of time. Ex TB, leprosy, syphilis
    • Latent disease = pathogen is inactive for long periods of time and then becomes active to produce symptoms
      • Ex. shingles
  • 14. Classifying infectious diseases
    • Herd immunity = when most of the population is immune through vaccination or acquired immunity, few susceptible people so its hard for pathogen to find
    • Local infections – limited to small area of body ex. Boils
    • Systemic or generalized infection – microbes or their products spread throughout the blood or lymphatic system
      • Bacteremia – bacteria in the blood, toxemia – toxins, viremia - viruses
  • 15. Classifying infectious diseases
    • Focal infection = local infection enters blood or lymph and spreads to other parts of body ex. Sinuses, tonsils
    • Sepsis = a toxic, inflammatory condition from spread of bacteria or their toxins from a local infection
      • Septicemia = sepsis from bacterial pathogens in the bloodstream
  • 16. Classifying infectious diseases
    • Sepsis = a toxic, inflammatory condition from spread of bacteria or their toxins from a local infection
      • Septicemia = sepsis from bacterial pathogens in bloodstream
    • Sub-clinical infection – does not cause any noticeable illness
    • Predisposing factors – makes the body more susceptible to a disease
      • Gender, genetics, weather, age etc.
  • 17. Development of disease – follows a certain sequence of events
    • Incubation period – the time between infection and signs and symptoms
    • Prodromal period – mild sxs of the disease
    • Ex. General aches, malaise
    • 3. Period of illness
      • a) Disease is most severe
      • b) Overt signs and sxs
      • c) # of WBCs may increase or decrease
      • d) If body doesn’t overcome the pathogen the px. May die
  • 18. Development of disease
    • 4. Period of decline
      • a) Signs and sxs subside
      • b) Px susceptible to secondary infection
    • 5. Period of convalescence
      • a) Px regains pre-diseased state
      • b) Px can serve as a reservoir of disease and spread infection to others
          • Ex. Typhoid fever, cholera
  • 19. Reservoirs of Infection
    • Reservoirs are sites that are a continual source of the pathogen from which they may be transmitted
    • All pathogens must have 1 or more reservoirs to exist
  • 20. Reservoirs of Infection
    • Human reservoirs
    • a) people harbor and transmit pathogens to others directly or indirectly
    • b) these people may be active carriers and are diseased and obvious transmitters or are healthy carriers and have no sxs
    • c) people are the only known reservoirs for smallpox, gonorrhea, measles, polio, etc.
    • d) smallpox was eradicated once the last known infected person was cured
  • 21. Reservoirs of Infection
    • The reservoir may be different from the source of the pathogen
      • Typhoid Mary was a reservoir of typhoid fever and shed typhoid bacilli in her feces
      • The immediate source would be water or food contaminated with the fecal material – she was a cook early 1900s
  • 22. Reservoirs of Infection
    • Animal reservoirs
      • Diseases that occur in wild and domestic animals that can be transmitted to humans are called zoonoses
      • Transmission is direct contact with infected animals or their hides, fur or feathers, contamination of food or water, insect vectors, or eating infected animal products
  • 23. Reservoirs of Infection
    • Nonliving reservoirs
      • Some organisms are able to survive and multiply in nonliving environments such as soil and water
      • Clostridium that causes tetanus and botulism can survive many years in the soil
      • Hookworms (a helminth) deposit their eggs into the soil
      • Water contaminated by human or animal feces cause GI tract disease (list includes bacteria, viruses, protozoa)
  • 24. Transmission of disease
    • Transmission is the mechanism by which an infectious agent is spread to a susceptible person
    • Contact transmission
      • Direct – person to person by kissing, touching, bites, or sexual intercourse
        • Colds, flu, STD’s
      • Droplet infection – pathogen spreads in saliva or mucus droplets by coughing or sneezing, travel short distance from reservoir
  • 25. Transmission of disease
    • Contact transmission cont.
      • Indirect – involves a nonliving objects = fomite ex. Cup, towel
    • Vehicle transmission
      • Inanimate reservoirs – food, water, blood
      • Airborne transmission – pathogens traveling in droplets or on dust for distances over 1 meter
        • Viruses, bacteria, fungal spores
  • 26. Transmission of disease
    • Vectors = animals that carry pathogens from 1 host to another, arthropods most important
    • Mechanical transmission – carry pathogens passively on their bodies and feet to food
    • Biological transmission – arthropod passes pathogen in a bite or feces which enter wound caused by the bite
  • 27. Nosocomial infections
    • Nosocomial infections are those infections acquired by pxs or hospital staff in a hospital or long term health care facility and account for 20,000 deaths/year in US
    • 3 conditions that compromise a host
      • Broken skin or mucous membranes
      • Suppressed immune system
      • Impaired defense cell activity – drugs, radiation, steroids, etc.
    • Pathogens transmitted by surgical procedures, fomites, medical equipment, air, H2O, people
  • 28. Emerging Infectious Diseases
    • Emerging infectious diseases show an increase in incidence or a potential for increase in the near future ex. West nile virus, SARS, whooping cough
    • Factors that contribute to emerging disease
      • New strains from genetic recombination
      • New serovars ex. Vibrio cholerae O139
      • Use of Abs and pesticides encourage growth
      • Global warming and weather changes may increase the distribution and survival of reservoirs and vectors
      • Diseases may spread to new geographic areas
  • 29. Epidemiology
    • Epidemiology = scientific study of the source and transmission of a disease with in a population
    • Epidemiology has a long hx
      • Hippocrates 460 -377 BC made observations about the link between malaria and yellow fever and swamps (breeding ground for the mosquito vector)
      • Edward Jenner – late 1700’s – observations of cowpox led to his vaccination for smallpox
  • 30. Epidemiology
    • Epidemiology
      • Ignaz Semmelweis – mid 1800s proved that childbed fever resulted from physicians not washing their hands after dissections
      • British epidemiologist John Snow investigated cholera outbreak in London
        • Most of the cholera victims lived in the Broad Street area and used the water from the Broad Street Pump
        • Removing the pump handle ended the cholera epidemic
  • 31. Epidemiology
    • Descriptive epidemiology – collecting all data that describes the occurrence of the disease
      • Info of affected individuals – place, time, age, M/F
      • Snow’s approach was descriptive
      • The approach is looking backwards
  • 32. Epidemiology
    • Analytical epidemiology – look for a common factor among the affected persons that might have preceded the disease
    • Experimental epidemiology tests a hypothesis ex. Effectiveness of a drug
      • 2 groups – 1 to receive the drug and 1 a placebo
      • Compare groups to determine if any difference with drug
  • 33. Center for Disease Control and Prevention (CDC)
    • Branch of US Public Health Service in Atlanta, Georgia – which is the central source of information in the US
    • CDC issues the Morbidity and Mortality Weekly Report (MMWR) at
    • Notifiable diseases – drs and health care workers must report to Public Health Service ex. AIDS, measles, gonorrhea, tetanus, typhoid fever