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Chapter 14

Chapter 14. Principles of Disease and Epidemiology. Principles of Disease and Epidemiology. Pathology Study of disease Disease in a state of not being healthy, change from health Pathogens disease causing organisms Etiology Study of the cause of a disease

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Chapter 14

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  1. Chapter 14 Principles of Disease and Epidemiology

  2. Principles of Disease and Epidemiology • Pathology Study of disease • Disease in a state of not being healthy, change from health • Pathogens disease causing organisms • Etiology Study of the cause of a disease • Pathogenesis Development of disease • Infection Colonization or invasion of pathogens, may be microbes in the wrong place (E. coli in the urinary tract)

  3. Normal Microbiota (Flora) and the Host • Normal Flora - the normal bacteria in you and on you • You have 1013 eucaryotic cells and 1014 prokaryotic cells • Within 8 - 12 hours of life you are colonized by normal flora (microbiota). • Breast feeding versus bottle - different organisms • Transient microbiota may be present for days, weeks, or months • Microbial antagonism • Normal microbiota overwhelm pathogens - no place for them to colonize • Intestines and vagina - excessive antibiotics disrupts balance • Vagina normally pH ~ 4 with Lactobacillus spp without can lead to Candida infections • Symbiosis is the relationship between normal microbiota and the host

  4. Normal Microbiota and the Host: • In commensalism, one organism is benefited and the other is unaffected. • In mutualism, both organisms benefit. • Be able to give a few examples of mutualistic bacteria • In parasitism, one organism is benefited at the expense of the other. • Some normal microbiota are opportunistic pathogens. • E. coli and urinary tract • Pneumocystis carinii and respiratory system • Streptococcus pneumoniae and pneumonia

  5. Normal Microbiota and the Host: • Locations of normal microbiota on and in the human body Figure 14.2

  6. Normal Microbiota and the Host: • Microbial antagonism is competition between microbes. • Normal microbiota protect the host by: • occupying niches that pathogens might occupy • producing acids • producing bacteriocins • Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect. • Lactobacillus spp

  7. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.1

  8. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. • Problems with Koch’s Postulates: • Not all diseases have bacterial etiologies • Genetic • Degenerative • Congenital • Exceptions • Not culturable • Treponema / Rickettsia / Chlamydia / viruses • Some pathogens cause many different diseases Figure 14.3.2

  9. Classifying Infectious Diseases • 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.

  10. Classifying Infectious Diseases Diseases may be grouped by how spread • 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. Example: Clostridium tetani

  11. By occurrence of Disease • 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. • 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. • Herd immunity Immunity in most of a population.

  12. By Severity or Duration of a Disease • Acute disease Symptoms develop rapidly • Chronic disease Disease develops slowly • Subacute disease Symptoms between acute and chronic • Latent disease Disease with a period of no symptoms when the patient is inactive Shingles

  13. By Extent of Host Involvement • Local infection Pathogens limited to a small area of the body • Systemic infection An infection throughout the body • Focal infection Systemic infection that began as a local infection • Bacteremia Bacteria in the blood • Septicemia Growth of bacteria in the blood

  14. 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 Pneumocystis pneumonia and AIDS • Subclinical disease No noticeable signs or symptoms (inapparent infection) Hepatitis / Typhoid mary / Polio

  15. Predisposing Factors • Make the body more susceptible to disease • Short urethra in females • Inherited traits such as the sickle-cell gene • Climate and weather • Fatigue and Stress • Age • Lifestyle • Chemotherapy • Gender

  16. Development of Disease Stages of Disease • Incubation infection up to first symptoms may or may not be variable • Prodromal short period of early mild symptoms -- malaise • Period of Illness overt signs -- fever and chills, swollen lymph nodes, GI disturbance increase in WBC’s • Period of Decline signs and symptoms subside - susceptible to 2˚ infections • Period of Convalescence regain strength and recovery BUT maybe reservoir

  17. The Stages of a Disease Figure 14.5

  18. Reservoirs of Infection • Reservoirs of infection are continual sources of infection. • Human — AIDS, gonorrhea • Carriers may have inapparent infections or latent diseases. • Carriers may be in pre-symptom stage or recovery of a disease - no symptoms • Animal — Rabies, Lyme disease • Some zoonoses may be transmitted to humans • Plague / psittacosis / swine flu / bird flu • Nonliving — Botulism, tetanus • Soil • Water - rivers, lakes, snow, oceans and laundry water

  19. Transmission of Disease • Three main routes • Contact - Direct or indirect • Vehicles - inanimate objects - e.g. food or drugs • Vectors - arthropods Contact • Direct Requires close association between infected and susceptible host • Indirect Spread by fomites (inanimate objects) glass, toothbrush or clothing • Droplet Transmission via airborne droplets

  20. Transmission of Disease Figure 14.6a & 8

  21. Transmission of Disease • VehicleTransmission by an inanimate reservoir (food, water) Shigella, cholera, airborne on dust aerosol >3’, tapeworm Staphylococci, Streptococci, tuberculosis, fungal spores -- histoplasmosis, coccidiodomycosis • Vectors Arthropods, especially fleas, ticks, and mosquitoes • Mechanical Arthropod carries pathogen on feet • BiologicalPathogen reproduces in vector and bites host. Dengue fever, Yellow fever, Malaria, encephalitis, plague, Lyme disease RMSF

  22. Transmission of Disease Figure 14.6b, c

  23. Nosocomial (Hospital-Acquired) Infections • Are acquired as a result of a hospital stay • 5-15% of all hospital patients acquire nosocomial infections Figure 14.7, 9

  24. Nosocomial Hospital acquired • 5 - 15% acquire >20,000 per year die • why? • a) microbes in environment -- (lots of sick people) • b) already sick or wounded -- compromised host • c) close to people - chain of transmission • Also resistant strains - E. coli, Pseudomonas, enterics like Serratia • Control by aseptic techniques • Antibiotic abuse

  25. Relative frequency of nosocomial infections Figure 14.10

  26. Common Causes of Nosocomial Infections

  27. Emerging Infectious Diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. • Contributing factors: • Evolution of new strains • V. cholerae O139 • Inappropriate use of antibiotics and pesticides • Antibiotic resistant strains • Changes in weather patterns • Hantavirus • Spread of human populations and travel

  28. Emerging Infectious Diseases • Contributing factors: • Modern transportation • West Nile virus • Ecological disaster, war, expanding human settlement • Coccidioidomycosis • Animal control measures • Lyme disease • Public Health failure • Diphtheria

  29. Epidemiology • The study of where and when diseases occur Figure 14.11

  30. Epidemiology

  31. Table 14.7

  32. Centers for Disease Control and Prevention (CDC) • Collects and analyzes epidemiological information in the U.S. • Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov Morbidity: incidence of a specific notifiable disease Mortality: deaths from notifiable diseases Morbidity rate = number of people affected/total population in a given time period Mortality rate - number of deaths from a disease/total population in a given time

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