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PRINCIPLES OF DISEASE

PRINCIPLES OF DISEASE. Symbiosis. Relationship between 2 or more species Mutualism- both benefit, . Symbiosis. Commensalism-one benefits and other unaffected. Parasitism. One benefits at expense of other Pathogen-causes disease Metabolically unstable relationship

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PRINCIPLES OF DISEASE

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  1. PRINCIPLES OF DISEASE

  2. Symbiosis • Relationship between 2 or more species • Mutualism- both benefit,

  3. Symbiosis • Commensalism-one benefits and other unaffected

  4. Parasitism • One benefits at expense of other • Pathogen-causes disease • Metabolically unstable relationship • Host dies or eliminates pathogen • Most successful parasites

  5. Parasitism • Host under continuous pressure from infection • Battle between host & parasite • Emergence of new & return of old infectious diseases

  6. Pathogenicity • Capacity to produce disease • Adherence • Multiply on host • Ability to invade host or cause damage • Avoid being damaged by host’ defenses • Depends upon # of organisms

  7. Virulence • Intensity of disease produced

  8. Terms • Contamination • Infection- multiples and invades tissue • Disease- disrupts state of health

  9. Normal Flora • 1 x10 13 body cells with 1 X1014 bacterial cell • Resident flora always present

  10. Normal Flora • Resident flora • Transient flora

  11. Opportunists • Usually cause no disease • Conditions allow them to cause disease

  12. Opportunists • Intro of bug into unusual body sites • Disturbance of normal flora

  13. Advantage of Normal Flora • Ensures normal development of immune system • Prevent over growth of harmful organism-microbial antagonism

  14. Microbial Antagonism • Normal flora in colon prevents overgrowth of C. difficile • E. coli produces bacteriocins

  15. Disadvantage of Normal Flora • Potential for spread into sterile parts of body • Intestine may perforate • Skin broken • Extraction of tooth • Perianal skin flora enters urinary tract

  16. Etiology • Cause of disease • Koch’s postulates-organism causes disease

  17. Frequency of Disease • Endemic • Always present in population • Epidemic • Occurs in unusually high number of people • Pandemic- • Epidemics world wide

  18. Types of Infectious Diseases • Acute -develops rapidly but lasts for short time- influenza • Chronic disease -develops more slowly and continues or recurs for long periods -TB, hepatitis B • Latent- agent remains inactive for a time and later becomes active-shingles

  19. Herd Immunity • Proportion of people in community who are immune • Important in cyclic diseases • If high, disease can only spread among susceptible people • Loss of herd can lead to reemergence of disease

  20. Extent of Disease • Local infection-limited to small area of body- boils • Focal - starts as local infection (sinus or teeth) then enter blood or lymph and spreads • Systemic -organisms or products spread through out body-measles • Bacteremia- presence of bacteria in blood

  21. Extent of Disease • Septicemia-bacteria multiplies in blood • Toxemia-toxins in blood • Viremia-virus in blood • Subclinical (inapparent )- no noticeable illness-hepatitis A • Primary disease- initial acute infection • Secondary infection -opportunistic infection

  22. Stages of Disease • Incubation period-time between initial infection and first appearance of S&S

  23. Prodromal Period • Short period–only in some diseases 

  24. Invasive Period • Period of illness-most acute • Overt signs and symptoms • Cough, sore throat

  25. Decline/Convalescence • S&S subside • Regain strength and recovery

  26. Epidemiology • Study of mechanism and factors involved in the frequency and spread of disease • Incidence of diseases • Prevalence of diseases

  27. Chain of Infection Infecting Agents Susceptible Host Bacteria Parasites Viruses Elderly & Young Pts w/ Chronic Illness Diabetic Use of Invasive Equip Reservoir People Food Equipment Entry Portal of Exit Broken Skin Respiratory System GI & GU System Respiratory System GI & GU System Direct Contact Indirect Contact Transmission Airborne Droplet

  28. Spread of Disease • Chain of infection • Agent- pathogen • Reservoir-source/site of organism • Human reservoirs • Animal reservoirs -zoonoses

  29. Humans • Sick people • Carriers • Incubatory or asymptomatic carriers • HIV but not AIDS • Hepatitis C • Chronic carriers • Typhoid Mary excreted salmonella for years in feces • S. pyogenes in throat

  30. Animals • Domestic and wild • Mammals carry rabies-exposure to saliva • Consume contaminated animals or products • Arthropod borne-West Nile • Zoonoses • Lyme disease: wild deer and mice • Hantavirus pulmonary disease: rodents

  31. Environmental Reservoirs • Able to survive in nonliving reservoirs • Soil: C. tetani • Humans produces toxin • Survives in soil by forming endospores • Contaminated water

  32. Portal of Exit • Via body fluid or feces • Respiratory tract • GI • GU • Nonintact skin-lesions, wounds

  33. Modes of Transmission • Airborne • Tiny droplet nuclei vs large droplets • Dust particles • Suspended in air don’t fall • More likely to reach lower resp tract • Resistant to drying • TB, measles and chicken pox • Spread rapidly in crowded conditions

  34. Droplet • Large droplets, short distances • Mucous droplets -coughing , sneezing • Pertussis, influenza, SARS • Talking less transmission

  35. Contact • Direct- person to person, touching ,sex, colds • Horizontal transmission • Fecal-oral transmission especially if public health & hygiene lacking

  36. Contact • Vertical • Parent to offspring-birth canal, breast milk, placenta • Indirect-via fomites-tissues, diapers , door knobs- hands • Normal person sheds skin atrr rate of 5 x10 8 per day • Hep B, C, D, lice, STDs

  37. Vehicle • Via medium-water, food, blood - Shigella in water or food, S. aureus • Vector-arthropod • Mechanical-passive • Biological- active

  38. Portals of Entry • Respiratory • GI - in food and water • GU-sexually transmitted microbes • Non intact skin- parenteral

  39. Susceptible Host • Imunocompromised • Old age or young • Not vaccinated • Large inoculum

  40. Healthcare Infections • Healthcare acquired • Exogenous • Endogenous

  41. Consequences • Serious illness or death • Prolonged hospital stay • Need for antimicrobial therapy • Foci for spreading infection

  42. Controlling Disease Transmission • Standard precautions-everyone • Isolation for communicable diseases or bugs

  43. Prevention • SSIs –prophylactic antibiotics • Devices- central lines & ventilators

  44. Prevention • Quarantine • Immunization- influenza & pneumococcal • Vector control

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