Chapter 14 epidemiology.cj


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Chapter 14 epidemiology.cj

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