Infectious Disease

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Infectious Disease
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Infectious Disease

• Globally, Infectious disease is still the single
  most common cause of death
• in 1993, gt16 million people died from infectious
  diseases
• Many diseases, previously considered conquered,
  have once again re-emerged
• Tuberculosis
• pneumonia
• food-borne illnesses

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Reemerging Infectious Disease
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Reemerging Infectious Disease

• Why?
• Human Demographics and Behavior
• Technology and Industry
• Economic development and Land Use
• Microbial Adaptation and Change
• Breakdown of Public Health Measures
• and Deficiencies in Public Health
• Infrastructure

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What is an Infectious disease?

• Communicable infection - a disease that is
  transmitted from person to person (NOT
  necessarily spread by direct contact!)
• influenza
• HIV
• tuberculosis
• chicken pox
• Noncommunicable infection - a disease that is not
  directly transmitted from person to person
• malaria
• botulism
• Rabies

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Reemerging

• Cryptosporidiosis (protozoan)
• Diphtheria (bacterium)
• Malaria (protozoan)
• Meningitis, necrotizing fasciitis (flesh-eating
  disease), toxic-shock syndrome, and other
  diseases Group A Streptococcus (bacterium)
• Pertussis (whooping cough) (bacterium)

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Reemerging

• Rubeola (measles)(virus)
• Schistosomiasis (helminth)
• Rabies (virus)
• Tuberculosis (bacterium) stricken)
• Yellow fever (virus)

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What causes infectious diseases?

• Microorganisms
• Bacteria
• Virus
• Prion
• Fungus
• Protozoa
• Helminth
• Products from microorganisms
• toxins

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Just how big are these guys anyway?
Bar is 10 microns

• viruses
• 0.05 to 0.1 microns
• bacteria
• 0.5 to 1.5 microns
• red blood cell
• 5 microns
• lymphocyte (white blood cell)
• 5 to 8 microns
• human sperm
• 60 microns

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Some Definitions

• Infectivity - capacity of an agent to enter
  replicate within a susceptible host
• Pathogenicity - capacity of an agent to cause
  clinical signs (disease) in a host
• Virulence - refers to the severity of disease
• Clinical disease - patient has noticeable
  symptoms of illness
• Subclinical disease - no apparent symptoms if
  infection persists, patient is known as a carrier

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Modes of Transmission
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Why do people get sick?

• Agent Factors
• new pathogens (HIV, Nile-like virus)
• changes in pathogens (acquire antibiotic
  resistant genes)
• Environmental Factors
• changes in environmental conditions (el niño)
• new environments (natural or man-made)
• (Sweetwater wetlands)

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Why do people get sick?, contd.

• Host Factors
• age
• gender
• ethnicity
• immune status
• nutritional status
• behavior
• Balance is Key!

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Are all bacteria bad?

• No!
• Some bacteria perform essential functions in the
  body such as
• skin prevents more harmful bacteria from
  colonizing
• intestines helps body break down and absorb
  certain nutrients prevents more harmful bacteria
  from causing intestinal infections
• vagina prevents yeasts from overgrowing and
  causing infections
• Other body areas are colonized and infections
  only occur in immunocompromised people
• nasopharynx, oropharynx, esophagus, stomach

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Prevention and Treatment

• Sanitation
• water and waste treatment
• personal hygiene
• Vaccination
• probably the 1 way to prevent communicable
  diseases
• Healthy living (avoidance)
• practice safe sex
• avoid IV drugs
• avoid hospital stays (5 of patients acquire a
  nosocomial infection)
• Antibiotics and other drugs
• use wisely and sparingly
• dont use antibiotics for viral infections

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Antibiotics

• Penicillin
• discovered in 1940s
• natural product of bread mold
• thought to be the miracle cure for all infections
• now many organisms are resistant
• Antibiotic Resistance
• antibiotics do not work on viral infections
• inappropriate use and overuse has resulted in
  many antibiotic resistant organisms (some
  organisms can transfer resistance between
  species)
• research into new antibiotics has fallen behind
• many multiply resistant organisms exist

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Your Immune System

• Part of the lymphatic system
• Primary lymphoid organs
• bone marrow
• spleen
• lymph nodes
• thymus
• Secondary lymphoid organs
• Peyers patches
• tonsils
• appendix
• mucosal associated lymphoid tissues (MALT)

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Immunity
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Cells of the Immune System

• Leukocytes (white blood cells)
• neutrophils (PMNs)
• monocyte/macrophage
• eosinophil
• basophil
• Specialized cells
• B-cells antibodies
• T-cells

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Innate immunity

• First-line defenses
• skin
• low pH, low moisture, normal desquamation,
  antibacterial substances
• vaginal epithelium
• low pH, normal flora,
• conjunctival epithelium
• flushing effects of tears, lysozyme, lactoferrin
• respiratory epithelium
• secretory IgA (sIgA), lysozyme, lactoferrin,
  mucociliary escalator
• gastrointestinal epithelium
• hydrochloric acid, gastric enzymes,mucus,sIgA,
  normal flora
• urinary epithelium
• flushing effects of urine

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Innate immunity

• Second-line defenses (occurs after organism
  breaches epithelial layer)
• Initial environment
• tissue fluids lysozyme, lactoferrin
• monocyte/macrophage engulf destroy
• NK cells recognize altered self cells
• lymphatic fluid drains tissues to lymph nodes

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Innate immunity

• Second-line defenses, contd.
• Inflammation - normal host response to a
  traumatic or infectious injury
• heat
• pain
• redness
• swelling
• loss of function

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Innate immunity

• Second-line defenses, contd.
• Phagocytic defenses (by order of appearance)
• PMNs -polymorphonuclear leukocytes (neutrophils)
• monocytes (in blood)
• macrophages (in tissue)

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Adaptive Immunity

• Cell-mediated
• T-cells(CD4, CD8)
• Humoral
• B-cells
• antibodies (immunoglobulins IgM, IgG, IgA, IgE,
  IgD)
• Both
• complement cascade

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Autoimmune Diseases

• Immune system fails to differentiate between self
  and non-self and generates antibodies against
  self proteins
• lupus - immune cells attack DNA
• arthritis - immune cells attack cartilage and
  bone
• multiple sclerosis - immune cells attack central
  nervous system

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Prevention
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Epidemiology
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Initial case investigation- looking at reported
cases of interest

• There are three questions to consider
• Who?
• Where?
• When?

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Who?

• Gender
• Age
• Occupation
• Cultural background
• Signs and symptoms

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Where?

• Physical location
• Open or enclosed
• High or low

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When?

• Time of day
• Time of Week
• Time of month and year
• Duration of event
• Sequence of events

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Epidemiological Guidelines

• 1. Investigate reported cases

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2. Form a Hypothesis
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3. Come up with a working case definition
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4. Design a questionnaire
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5. Apply questionnaire to cases and controls

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6. Refine case definition, refine hypothesis

• Identify similarities
• Assemble identified case reports
• Exclude disqualified reports
• Test hypothesis against identified cases

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Take Action
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8. Communicate Findings