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Epidemiology of Infectious disease

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Title: Epidemiology of Infectious disease


1
Epidemiology of Infectious disease
2
Symbiotic Relationships Between Microbes and
Their Hosts
  • Symbiosis means to live together
  • We have symbiotic relationships with countless
    microorganisms
  • Types of symbiosis
  • Mutualism
  • Commensalism
  • Parasitism

3
Symbiotic Relationships Between Microbes and
Their Hosts
4
Infection
  • Mutualsim Each one benefits
  • Commensual One organism benefits, the other is
    not harmed.
  • Parasitism Advantage to one, disadvantage to
    the other.
  • Obligate relationship one depends on the other
    for survival (parasites are obligate pathogens)

5
  • Normal Flora Organism is always on or in us
    GI, GU, oral mucosa.
  • Sterile areas of the body Blood, CSF. Any
    organism here indicates something is wrong. The
    first indicator is decreased glucose, increased
    protein
  • Opportunistic Pathogens A normal flora organism
    that becomes a pathogen when the hosts immune
    defense decreases.
  • Trauma, Surgery, Burns overcomes barriers of
    defense
  • Catheterization allows increased access and
    decreased defense
  • Chemotherapy e.g. ablative (for CA) destroys
    bone marrow,
  • therefore myeloid and
    lymphoid immunity goes down.
  • Co-infection e.g. haemophilic influenza is 2
    to viral influenza.

6
Tissue Tropism
  • Tissue Tropism (organisms are selective of
    tissues they infect) influenza does not affect
    your hand gonorrhea only effects mucosa.
    Tropism can also be species, organ, or
    non-specific.
  • HIV integrates a provirus into our chromosome.
    Antibodies actually assist the HIV organisms
    because opsinization helps to internalize the
    virus. Because of almost no cell mediated
    immunity (T-cells are infected), AIDS patients
    die from TB, cytomegalovirus (CMV), Candida,
    pneumocystis. When a person has a second
    infection, it is called a CO-INFECTION.

7
OBLIGATE PATHOGENS
  • Will always cause infection and disease whenever
    and wherever they are encountered (e.g. Yersinia
    pestis plague, anthrax, smallpox) unless you are
    immune. However, they dont want to kill their
    host.

8
Virulence
  • VIRULENCE Ability to cause infection and
    disease.
  • MULTIPLICITY OF INFECTION (INNOCULUM) the
    number of organisms needed to cause disease.
    There is an inverse relationship between
    virulence and Multiplicity of Infection. If only
    a few bacterial cells cause the disease, it is
    said to be very virulent.
  • Obligate pathogens are virulent, even with a low
    inoculum, because they are effective. Most
    innoculum needs 103-5 organisms. Only 10
    organisms can form an innoculum in a virulent
    organism such as anthrax.
  • Anthrax avoids immune defenses by exploiting the
    very mechanisms used to fight it. It becomes
    activated after phagocytosis.
  • Mycobacterium will coat the wall of vacuoles so
    lysozymes cant fuse.
  • Rickettsia is on a timer, and escapes the vacuole
    to invade the nucleus.

9
PORTALS OF ENTRY (POE)
  • CEPHALIC (7 PORTALS) Mouth, nose, eyes, ears.
  • CORPOREAL Mammary, Vaginal, Urethral, Rectal
  • TRAUMA/MEDICAL Burn, Compound Fracture,
    surgical/catheter, injury/IVDA, abnormal mucosa
    (CA chemo).

10
MODES OF TRANSMISSION (MOT)
  • AEROSOL Airborne micro-particles (soil aerosol
    containing endospores)
  • DROPLET NUCLEI Mucoid micro-droplet via cough
    or sneeze, durable on surfaces, mainly
    transmitted by contact. Sneeze and cough into
    your elbow!
  • DIRECT CONTACT Direct object/tissue-to-tissue
    contact.
  • CASUAL TRANSMISSION handshake, clothing
  • ASPIRATION inhalation of oral, GI, or
    food-borne organisms
  • FECAL-ORAL autoinoculation or contamination
  • (poor
    hygiene)
  • SEXUAL TRANSMISSION (STD) sexual/bodily fluid
    contact

11
AGENTS OF TRANSMISSION
  • VECTOR a living organism that spreads disease
    from one host to another.
  • (mosquitoes, ticks, rats, humans)
  • FOMITE inanimate object that spreads disease
    from one host to another.
  • (toothbrush, water glass, toys, handles)

12
HOST-PATHOGEN RELATIONSHIP (HPR)
  • INFECTION presence of organism
  • DISEASE adverse symptoms due to infection
  • NORMAL FLORA organism typically found on
    healthy individual
  • PATHOGEN organism causing disease (etiologic
    agent)
  • IMMUNOCOMPROMISED suppressed or deficient
    immunity
  • NOSOCOMIAL acquired in hospital setting
  • COMMUNITY-ACQUIRED acquired in routine,
    day-to-day activities
  • OPPORTUNISTIC PATHOGEN normal flora
    compromised ? pathogen
  • OBLIGATE PATHOGEN always causes Dz if present
  • PATHOGENESIS (Px) events leading to Dz (POE?Dz)
  • MULTIPLICITY OF INFECTION (MOI) inoculum
    required for infxn
  • INCUBATION (INC) time from transmission to Dz
  • VIRULENCE measure of Dz capability
  • VIRULENCE FACTOR (VF) ultrastructure,
    exoenzyme, or exotoxin

13
BACTERIAL SYMPTOM TERMINOLOGY
  • BACTEREMIA bacteria in bloodstream
  • BACTERURIA bacteria in urine (normal or
    pathogenic flora)
  • SEPTICEMIA Gram negative bacteremia in the
    bloodstream
  • PYEMIA Gram bacteremia
  • PYROGENIC fever-producing infection or
    bacterial components
  • PURULENT pus-producing, reaches an opening to
    drain out. The pus is a collection of dead
    neutrophils, which are the 1 immune cells when
    there is pus.
  • GRANULOMATOUS infxn where macrophages are 1
    immune cells (no pus)
  • DIFFERENTIAL DIAGNOSIS (DDx) all possible
    causes of the disease.
  • UROSEPSIS Septicemia from UTI
  • FACULTATIVE INTRACELLULAR PARASITES are not
    obligate pathogens. They can survive temporarily
    in white cells, such as neutrophils, Monocytes/
    Macrophages.
  • EXOTOXINS A toxin made and then secreted, e.g.
    pesticin, hemolysins, shigatoxins, choleragen,
    enterotoxins, plasminogen activating factor,
    coagulase, etc.
  • ENDOTOXINS A component of the cell wall is
    toxic to us, e.g. LPS and LOS.

14
Symbiotic Relationships Between Microbes and
Their Hosts
  • Normal Microbiota in Hosts
  • Also termed normal flora and indigenous
    microbiota
  • Organisms that colonize the bodys surfaces
    without normally causing disease
  • Two types
  • Resident microbiota
  • Transient microbiota

15
Symbiotic Relationships Between Microbes and
Their Hosts
  • Resident microbiota
  • Are a part of the normal microbiota throughout
    life
  • Are mostly commensal
  • Transient microbiota
  • Remain in the body for short period
  • Found in the same regions as resident microbiota
  • Cannot persist in the body
  • Competition from other microorganisms
  • Elimination by the bodys defense cells
  • Chemical or physical changes in the body

16
Symbiotic Relationships Between Microbes and
Their Hosts
  • Acquisition of normal microbiota
  • Development in womb free of microorganisms
    (axenic)
  • Microbiota begin to develop during birthing
    process
  • Much of ones resident microbiota established
    during first months of life

17
Symbiotic Relationships Between Microbes and
Their Hosts
  • How Normal Microbiota Become Opportunistic
    Pathogens
  • Opportunistic pathogens
  • Normal microbiota that cause disease under
    certain circumstances
  • Conditions that provide opportunities for
    pathogens
  • Introduction of normal microbiota into unusual
    site in body
  • Immune suppression
  • Changes in the normal microbiota
  • Changes in relative abundance may allow
    opportunity for a member to thrive and cause
    disease

18
Inflammation
19
Host defense summary
What can you catch from a toilet seat?
20
Cell surface markers
  • Designated as CD
  • Cluster of Differentiation
  • used to identify specific structures on a cell
  • 200 different designations

21
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22
Reservoirs of Infectious Diseases of Humans
  • Most pathogens cannot survive for long outside of
    their host
  • Reservoirs of infection
  • Sites where pathogens are maintained as a source
    of infection
  • Three types of reservoirs
  • Animal reservoir
  • Human carriers
  • Nonliving reservoir

23
Reservoirs of Infectious Diseases of Humans
  • Animal Reservoirs
  • Zoonoses
  • Diseases naturally spread from animal host to
    humans
  • Acquire zoonoses through various routes
  • Direct contact with animal or its waste
  • Eating animals
  • Bloodsucking arthropods
  • Humans are usually dead-end host to zoonotic
    pathogens

24
Reservoirs of Infectious Diseases of Humans
  • Human Carriers
  • Infected individuals who are asymptomatic but
    infective to others
  • Some individuals eventually develop illness while
    others never get sick
  • Healthy carriers may have defensive systems that
    protect them

25
Reservoirs of Infectious Diseases of Humans
  • Nonliving Reservoirs
  • Soil, water, and food can be reservoirs of
    infection
  • Presence of microorganisms often due to
    contamination by feces or urine

26
The Movement of Microbes into Hosts Infection
  • Exposure to Microbes Contamination and Infection
  • Contamination
  • The mere presence of microbes in or on the body
  • Infection
  • When organism evades bodys external defenses,
    multiplies, and becomes established in the body

27
The Movement of Microbes into Hosts Infection
  • Portals of Entry
  • Sites through which pathogens enter the body
  • Four major pathways
  • Skin
  • Mucous membranes
  • Placenta
  • Parenteral route (intravenous)

28
Routes by which humans acquire parasitic
infections
Figure 23.1
29
Routes of entry for invading pathogens
30
Portals of exit
31
The Movement of Microbes into Hosts Infection
  • Portals of Entry
  • Skin
  • Outer layer of dead skin cells acts as a barrier
    to pathogens
  • Some pathogens can enter through openings or cuts
  • Others enter by burrowing into or digesting outer
    layers of skin

32
The Movement of Microbes into Hosts Infection
  • Portals of Entry
  • Mucous membranes
  • Line the body cavities that are open to the
    environment
  • Provide a moist, warm environment hospitable to
    pathogens
  • Respiratory tract is the most common site of
    entry
  • Entry is through the nose, mouth, or eyes
  • Gastrointestinal tract may be route of entry
  • Must survive the acidic pH of the stomach

33
The Movement of Microbes into Hosts Infection
  • Portals of Entry
  • Placenta
  • Typically forms effective barrier to pathogens
  • Pathogens may cross the placenta and infect the
    fetus
  • Can cause spontaneous abortion, birth defects,
    premature birth

34
The Movement of Microbes into Hosts Infection
  • Portals of Entry
  • Parenteral route
  • Not a true portal of entry
  • Pathogens deposited directly into tissues beneath
    the skin or mucous membranes (needle injection or
    i.v.)

35
The Movement of Microbes into Hosts Infection
  • The Role of Adhesion in Infection
  • Process by which microorganisms attach themselves
    to cells
  • Required to successfully establish colonies
    within the host
  • Adhesion factors include
  • Specialized structures (acts like Velcro)
  • Attachment proteins (acts like glue)
  • The presence of adhesions are considered a
    virulence factor.

36
The Movement of Microbes into Hosts Infection
  • The Role of Adhesion in Infection
  • Attachment proteins help in adhesion
  • Found on viruses and many bacteria
  • Viral or bacterial ligands (proteins) bind host
    cell receptors
  • Interaction can determine host cell specificity
  • Changing/blocking a ligand or its receptor can
    prevent infection
  • Inability to make attachment proteins or adhesins
    renders microorganisms avirulent
  • Some bacterial pathogens attach to each other to
    form a biofilm

37
The Nature of Infectious Disease
  • Infection is the invasion of the host by a
    pathogen
  • Disease results if the invading pathogen alters
    normal body functions
  • Disease is also referred to as morbidity

38
The Nature of Infectious Disease
  • Manifestations of Disease Symptoms, Signs, and
    Syndromes
  • Symptoms
  • Subjective characteristics of disease felt only
    by the patient
  • Signs
  • Objective manifestations of disease observed or
    measured by others
  • Syndrome
  • Symptoms and signs that characterize a disease
    or abnormal condition
  • Asymptomatic, or subclinical, infections lack
    symptoms but may still have signs of infection

39
The Nature of Infectious Disease
  • Cause of Disease Etiology
  • Study of the cause of disease
  • Germ theory of disease
  • Disease caused by infections of pathogenic
    microorganisms
  • Robert Koch developed a set of postulates one
    must satisfy to prove a particular pathogen
    causes a particular disease

40
Kochs Postulates
41
The Nature of Infectious Disease
  • Causation of Disease Etiology
  • Exceptions to Kochs postulates
  • Some pathogens cant be cultured in the
    laboratory
  • Diseases caused by a combination of pathogens and
    other cofactors
  • Ethical considerations prevent applying Kochs
    postulates to pathogens that require a human host
  • Difficulties in satisfying Kochs postulates
  • Diseases can be caused by more than one pathogen
  • Pathogens that are ignored as potential causes of
    disease

42
The Nature of Infectious Disease
  • Virulence Factors of Infectious Agents
  • Pathogenicity
  • Ability of a microorganism to cause disease
  • Virulence
  • Degree of pathogenicity (how good is it at its
    job?)
  • Virulence factors contribute to virulence
  • Adhesion factors
  • Biofilms
  • Extracellular enzymes
  • Toxins
  • Antiphagocytic factors

43
The Nature of Infectious Disease
  • Virulence Factors of Infectious Agents
  • Extracellular enzymes
  • Secreted by the pathogen
  • Dissolve structural chemicals in the body
  • Help pathogen maintain infection, invade, and
    avoid body defenses

44
The Nature of Infectious Disease
  • Virulence Factors of Infectious Agents
  • Toxins
  • Chemicals that harm tissues or trigger host
    immune responses that cause damage
  • Toxemia refers to toxins in the bloodstream that
    are carried beyond the site of infection
  • Two types
  • Exotoxins (made and secreted)
  • Endotoxins (part of the bacterial cell wall)

45
The Nature of Infectious Disease
46
The Nature of Infectious Disease
  • Virulence Factors of Infectious Agents
  • Antiphagocytic factors
  • Factors prevent phagocytosis by the hosts
    phagocytic cells
  • Bacterial capsule
  • Composed of chemicals not recognized as foreign
  • Slippery difficult for phagocytes to engulf
    bacteria
  • Antiphagocytic chemicals
  • Prevent fusion of lysosome and phagocytic
    vesicles
  • Leukocidins directly destroy phagocytic white
    blood cells

47
The Nature of Infectious Disease
  • The Stages of Infectious Disease
  • The disease process occurs following infection
  • Many infectious diseases have five stages
    following infection
  • Incubation period
  • Prodromal period
  • Illness
  • Decline
  • Convalescence

48
The stages of infectious disease
49
The Movement of Pathogens Out of Hosts Portals
of Exit
  • Pathogens leave host through portals of exit
  • Many portals of exit are the same as portals of
    entry
  • Pathogens often leave hosts in materials the body
    secretes or excretes

50
Portals of exit
51
Modes of Infectious Disease Transmission
  • Transmission is from a reservoir or a portal of
    exit to another hosts portal of entry
  • Three groups of transmission
  • Contact transmission
  • Direct, indirect, or droplet
  • Vehicle transmission
  • Airborne, waterborne, or foodborne
  • Vector transmission
  • Biological or mechanical

52
Classification of Infectious Diseases
  • Diseases can be classified in number of ways
  • The body system they affect
  • GI system, nervous system, blood
  • Taxonomic categories
  • Viral disease, Gram
  • Their longevity and severity
  • Chronic vs. acute mild vs. severe
  • How they are spread to their host
  • STD, blood borne, food
  • The effects they have on populations (rather than
    on individuals) global/pandemic vs. epidemic

53
Classification of Infectious Diseases
  • Terms used to classify infectious disease
  • Acute disease (rapid onset, short duration)
  • Chronic disease (long duration)
  • Subacute disease (slower onset, medium duration)
  • Latent disease (present but not obvious system)
  • Communicable (Contagious)

54
Epidemiology of Infectious Diseases
INFECTION Presence of microbe DISEASE
Symptomatic consequence of infection
55
Epidemiology
  • Epidemiology is the study of the patterns,
    causes, and effects of health and disease
    conditions in defined populations. It is the
    cornerstone of public health by identifying risk
    factors for disease and provides information for
    preventive healthcare.
  • Major areas of epidemiological study include
    disease etiology, outbreak investigation, disease
    surveillance and screening, biomonitoring, and
    comparisons of treatment effects such as in
    clinical trials.

56
John Snow
  • Dr. John Snow is known as the father of modern
    epidemiology. He showed that cholera was
    water-borne, and debunked the Miasma theory,
    which stated that cholera came from bad air. 

57
John Snow
  • John Snow was a British physician in London in
    1854, where a major cholera outbreak struck the
    nearby city of Soho.
  • In three days, 127 people who lived near Broad
    Street died of Cholera. Within a week, 500 people
    had died and one in seven people who developed
    cholera eventually died from it.
  • John Snow suspected contamination of the water,
    but couldnt find any organic matter in it.
    Almost all the cases of cholera occurred close to
    the Broad Street Water Pump.
  • Snow mapped out the cases of cholera in relation
    to the water pump.

58
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59
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60
  • The evidence Snow presented convinced the local
    council to remove the pump handle, halting the
    spread of the disease. It wasnt until 1885, when
    Robert Koch identified V. cholerae as the
    bacillus causing the disease that he had proof of
    his theory. He was right, but wasnt around to
    see this discovery himself. John Snow died four
    years later, at the age of 45. 

61
Epidemiology of Infectious Diseases
  • Frequency of Disease
  • Track occurrence of diseases using two measures
  • Incidence
  • Number of new cases of a disease in a given area
    during a given period of time
  • Prevalence
  • Number of total cases of a disease in a given
    area during a given period of time
  • Occurrence also evaluated in terms of frequency
    and geographic distribution

62
The incidence and estimated prevalence of AIDS
63
Epidemiologists report data in a number of ways
64
Different terms for the occurrence of disease
65
Epidemics Defined Relative to Expected Number of
Cases
66
Epidemiology of Infectious Diseases
  • Epidemiological Studies
  • Descriptive epidemiology
  • Careful tabulation of data concerning a disease
  • Record location and time of the cases of disease
  • Collect patient information
  • Try to identify the index case (or first case) of
    the disease

67
Epidemiology of Infectious Diseases
  • Epidemiological Studies
  • Analytical epidemiology
  • Seeks to determine the probable cause (etiology),
    mode of transmission, and methods of prevention
  • Useful in situations when Kochs postulates cant
    be applied
  • Often retrospective
  • Investigation occurs after an outbreak has
    occurred

68
Epidemiology of Infectious Diseases
  • Epidemiological Studies
  • Experimental epidemiology
  • Involves testing a hypothesis concerning the
    cause of a disease
  • Application of Kochs postulates is experimental
    epidemiology

69
Endemic
  • 1 characteristic of or prevalent in a particular
    field, area, or environment
  • 2 restricted or peculiar to a locality or region
  • Endemic" means "in the population."
  • "Endemic" is often used to characterize diseases
    that are generally found in a particular area
    malaria, for example, is said to be endemic to
    tropical and subtropical regions. This use
    differs from that of the related word "epidemic"
    in that it indicates a more or less constant
    presence in a particular population or area
    rather than a sudden, severe outbreak within that
    region or group. The word is also used by
    biologists to characterize the plant and animal
    species that are only found in a given area.

70
Epidemic
  • Affecting or tending to affect a disproportionatel
    y large number of individuals within a
    population, community, or region at the same time 

71
Demographics
  • The changes (such as the number of births,
    deaths, marriages, and illnesses) that occur over
    a period of time in human populations also  a
    set of such changes.
  • The demographics of a particular disease would
    include the ratio of males to females that have
    the disease, the average age, the geographical
    distribution, and the incidence (the likelihood
    of a person getting the disease) in a particular
    Country.

72
Epidemiology of Infectious Diseases
  • Hospital Epidemiology Nosocomial Infections
  • Types of nosocomial infections
  • Exogenous
  • Pathogen acquired from the health care
    environment
  • Endogenous
  • Pathogen arises from normal microbiota due to
    factors within the health care setting
  • Iatrogenic
  • Results from modern medical procedures

73
The interplay of factors that result in
nosocomial infections
74
Epidemiology of Infectious Diseases
  • Hospital Epidemiology Nosocomial Infections
  • Control of nosocomial infections
  • Precautions designed to reduce factors that
    result in disease
  • Hand washing is the most effective way to reduce
    nosocomial infections

75
Epidemiology of Infectious Diseases
  • Epidemiology and Public Health
  • Agencies at the local, state, national, and
    global level share information concerning disease
  • The United States Public Health Service
  • World Health Organization (WHO)
  • Public health agencies work to limit disease
    transmission
  • Monitor water and food safety
  • Public health agencies campaign to educate the
    public on healthful choices to limit disease

76
Basic Principles of Microbial Control
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