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Infectious Disease. Infectious Disease. Globally, Infectious disease is still the single most common cause of death in 1993, >16 million people died from infectious diseases Many diseases, previously considered conquered, have once again re-emerged Tuberculosis pneumonia

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Infectious Disease

  • Globally, Infectious disease is still the single most common cause of death

    • in 1993, >16 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

  • 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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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

What is an Infectious disease?


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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)

Reemerging


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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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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

    • don’t 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

      • Peyer’s patches

      • tonsils

      • appendix

      • mucosal associated lymphoid tissues (MALT)



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Cells of the Immune System

  • Leukocytes (white blood cells)

    • neutrophils (PMN’s)

    • 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, cont’d.

    • 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, cont’d.

    • Phagocytic defenses (by order of appearance)

      • PMN’s -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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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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6. Refine case definition, refine hypothesis

  • Identify similarities

  • Assemble identified case reports

  • Exclude disqualified reports

  • Test hypothesis against identified cases




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