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MicrobeHuman Interactions Infection and Disease

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Title: MicrobeHuman Interactions Infection and Disease


1
Microbe-Human Interactions- Infection and
Disease
2
The Human Host
  • Constantly exposure to microbes
  • Humans excellent hosts for microorganisms
  • May lead to infection pathogenic microorganisms
    penetrate the host defenses, enter the tissues,
    and multiply
  • Infectious disease the disruption of a tissue
    or organ caused by microbes or their products

3
Symbiotic Relationships
  • Symbiosis means to live together
  • Describes the relationship between microorganisms
    and their human hosts
  • Three types
  • Mutualism
  • Commenalism
  • Parasitism

4
The Three Types of Symbiotic Relationships
5
Resident Biota
  • Resident Biota The Human as a Habitat
  • Cell for cell, microbes on the human body
    outnumber human cells at least ten to one
  • Human Microbiome Project

6
Resident Microbiota
7
Resident Microbiota
8
Axenic (A-Zen-ik) or sterile sites in the human
host
9
Biota
  • Microbial antagonism- resident biota may benefit
    the human host by preventing the overgrowth of
    harmful microorganisms
  • Hosts with compromised immune systems could be
    infected by their own biota
  • Endogenous infections caused by biota that are
    already present in the body

10
Acquisition of Normal Microbiota
  • Development in the womb is generally free of
    microorganisms
  • Microbiota begins to develop during the birthing
    process
  • Much of ones resident microbiota established
    during the first months of life

11
Initial Colonization of the Newborn
Figure 13.1
12
The Progress of an Infection
  • Pathogen a microbe whose relationship with its
    host is parasitic and results in infection and
    disease
  • Type and severity of infection depend on
    pathogenicity of the organism and the condition
    of its host

13
Pathogenicity
  • Pathogenicity an organisms potential to cause
    infection or disease
  • True pathogens
  • Opportunistic pathogens
  • -Normal microbiota or other normally harmless
    microbes that can cause disease under certain
    circumstances

14
Conditions that provide opportunities for
pathogens
15
Virulence
  • Virulence is the degree of pathogenicity
  • Determined by its ability to
  • Establish itself in the host
  • Cause damage
  • Virulence factor any characteristic or
    structure of the microbe that contributes to its
    virulence
  • Different healthy individuals have widely varying
    responses to the same microorganism hosts evolve

16
Becoming Established Step One- Portals of Entry
  • Microbe enters the tissues of the body by a
    portal of entry
  • Major portals
  • Skin
  • Gastrointestinal tract
  • Respiratory tract
  • Urogenital tract
  • Placenta
  • Perinatal route
  • Source of infectious agent
  • Exogenous (external)
  • Endogenous (internal)

17
Infectious Agents that Enter the Skin
  • Outer layer of packed, dead, skin cells usually
    acts as a barrier to pathogens- few microbes can
    penetrate
  • Nicks, abrasions, punctures and insect bites
    -possible entry points
  • Some create their own passageways using digestive
    enzymes or bites
  • Examples
  • Staphylococcus aureus (boils)
  • Streptococcus pyogenes (impetigo)
  • Haemophilus aegyptius (pink eye)
  • Chalmydia trachomatis (trachoma)
  • Neisseria gonorrhoeae (gonorrhoea)

18
The Gastrointestinal Tract as Portal
  • Pathogens contained in food, drink, and other
    ingested substances
  • Adapted to survive digestive enzymes and pH
    changes
  • Examples of enteric pathogens
  • Gram-negative rods- Salmonella, Shigella, Vibrio,
    Certain strains of Escherichia coli,
  • Viruses- Poliovirus, Hepatitis A virus,
    Echovirus, Rotavirus,
  • Protozoa- Entamoeba hitolytica, Giardia lamblia

19
The Respiratory Portal of Entry
  • The portal of entry for the greatest number of
    pathogens
  • Examples
  • Streptococcal sore throat, Meningitis,
    Diphtheria, Whooping cough, Influenza, Measles,
    Mumps, Rubella, Chickenpox, Common cold, Bacteria
    and fungi causing pneumonia

20
Urogenital Portals of Entry
  • Sexually transmitted diseases (STDs)
  • Enter skin or mucosa of penis, external
    genitalia, vagina, cervix, and urethra
  • Some can penetrate an unbroken surface
  • Examples
  • Syphilis
  • Gonorrhea
  • Genital warts
  • Chlamydia
  • Herpes

21
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22
Pathogens that Infect During Pregnancy and Birth
  • Some microbes can cross the placenta (ex. the
    syphilis spirochete)
  • Other infections occur perinatally when the child
    is contaminated by the birth canal
  • TORCH (toxoplasmosis, other diseases, rubella,
    cytomegalovirus, and herpes simplex)

23
Some Pathogens that Cross the Placenta
24
Figure 13.3
25
The Size of the Inoculum
  • The quantity of microbes in the inoculating dose
  • For most agents, infection only proceeds if the
    infectious dose (ID) is present
  • Microorganisms with smaller IDs have greater
    virulence

26
Becoming Established Step Two- Attaching to the
Host (Adhesion)
Adhesion- attachment to host Mediated by
- adhesion factors - specialized
structures (e.x. adhesion discs
on some protozoa) - adhesion proteins
- match receptor molecules on
host (e.x. adhesins found of
fimbrae)
Figure 13.4
27
Adhesion and invasion of enteropathogenic
bacteria into human epithelial cells.
28
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29
Becoming Established Step Three- Surviving Host
Defenses
  • Phagocytes
  • White blood cells that engulf and destroy
    pathogens
  • Antiphagocytic factors used by some pathogens
    to avoid phagocytes
  • Leukocidins toxic to white blood cells,
    produced by Streptococcus and Staphylococcus
  • Extracellular surface layer makes it difficult
    for the phagocyte to engulf them, for example-
    Streptococcus pneumonia, Salmonella typhi,
    Neisseria meningitides, and Cryptococcus
    neoformans
  • Some can survive inside phagocytes after
    ingestion Legionella, Mycobacterium, and many
    rickettsias

30
Virulence Factors of Infectious Disease
  • Pathogenicity ability of a microorganism to
    cause disease
  • Virulence degree of pathogenicity
  • Virulence factors contribute to an organisms
    virulence
  • Adhesion factors
  • Biofilms
  • Extracellular enzymes
  • Toxins
  • Antiphagocytic factors

31
Causing Disease How Virulence Factors
Contribute to Tissue Damage
  • Exoenzymes
  • Enzymes secreted by the pathogen
  • Dissolve structural chemicals in the body
  • Help pathogen maintain infection, invade further,
  • and avoid body defenses (ex. Mucinase,
    collegenase,
  • coagulase, kinase)

32
Bacterial Toxins
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 (secreted from living bacterial
cells e.x. hemolysins) Endotoxins (not secreted-
part of outer membrane released from cell)
33
Figure 13.6
34
Comparison of endo- and exotoxins
35
The Stages of Infectious Disease
  • Following infection, sequence of events called
    the disease process occurs
  • Many infectious diseases have five stages
    following infection
  • Incubation period
  • Prodromal period
  • Illness
  • Decline
  • Convalescence

36
The Stages of Infectious Disease
Figure 14.10
37
Incubation periods for selected infectious
diseases
38
The Process of Infection and Disease
  • Establishment, Spread, and Pathologic Effects
  • Microbes eventually settle in a particular target
    organ and continue to cause damage at the site
  • Frequently weakens host tissues
  • Necrosis accumulated damage leads to cell and
    tissue death
  • Patterns of Infection

39
Figure 13.7
40
Signs and Symptoms Warning Signals of Disease
  • Sign any objective evidence of disease as noted
    by an observer
  • Symptom the subjective evidence of disease as
    sensed by the patient
  • Syndrome when a disease can be identified or
    defined by a certain complex of signs and
    symptoms
  • Asymptomatic, or subclinical, infections lack
    symptoms but may still have signs of infection

41
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42
Signs and Symptoms of Inflammation
  • Fever, pain, soreness, swelling
  • Edema- accumulation of fluid
  • Granulomas and abscesses- walled-off collections
    of inflammatory cells and microorganisms
  • Lymphadenitis- swollen lymph nodes
  • Lesion the site of infection or disease

43
Signs of Infection in the Blood
  • Changes in the number of circulating white blood
    cells
  • Leukocytosis- increase in level of white blood
    cells
  • Leukopenia - decrease in level of white blood
    cells
  • Septicemia general state in which
    microorganisms are multiplying in the blood and
    are present in large numbers
  • Bacteremia or viremia microbes are present in
    the blood but are not necessarily multiplying

44
Movement of Pathogen Out of Host
  • Pathogens leave host through portals of exit

45
Exit Portals
  • Respiratory and Salivary Portals
  • Coughing and sneezing
  • Talking and laughing
  • Skin Scales
  • Fecal Exit
  • Urogenital Tract
  • Removal of Blood or Bleeding

46
The Persistence of Microbes and Pathologic
Conditions
  • Latency a dormant state
  • The microbe can periodically become active and
    produce a recurrent disease
  • Examples
  • Herpes simplex
  • Herpes zoster
  • Hepatitis B
  • AIDS
  • Epstein-Barr
  • Sequelae long-term or permanent damage to
    tissues or organs

47
Reservoirs Where Pathogens Persist
  • Reservoir the primary habitat in the natural
    world from which a pathogen originates
  • Source the individual or object from which an
    infection is actually acquired
  • Living Reservoirs
  • Carrier an individual who inconspicuously
    shelters a pathogen and spreads it to others
    without any notice
  • Asymptomatic carriers
  • Incubation carriers (HIV)
  • Convalescent carriers (Diptheria)
  • Chronic carrier (long-term carriage e.x. herpes,
    tuberculosis)
  • Passive carrier (e.x. transfer of nosocomial
    infections by care-givers)

48
Figure 13.9
49
Animals as Reservoirs and Sources
  • Vector a live animal that transmits an
    infectious agent from one host to another
  • Majority are arthropods
  • Larger animals can also be vectors
  • Biological vector actively participates in a
    pathogens life cycle
  • Mechanical vectors transport the infectious
    agent without being infected

50
Figure 13.10
51
Zoonosis
  • Zoonosis an infection indigenous to animals but
    naturally transmissible to humans
  • Human does not contribute to the persistence of
    the microbe
  • Can have multi-host inovlement
  • At least 150 worldwide
  • Example SWINE-FLU!

52
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53
Nonliving Reservoirs
  • Human hosts in regular contact with environmental
    sources
  • Soil
  • Water

54
The Acquisition and Transmission of Infectious
Agents
  • Communicable disease when an infected host can
    transmit the infectious agent to another host and
    establish infection in that host
  • Transmission can be direct or indirect
  • Contagious agent highly communicable
  • Noncommunicable disease does not arise through
    transmission of the infectious agent from host to
    host
  • Acquired through some other, special circumstance
  • Compromised person invaded by his or her own
    microbiota
  • Individual has accidental contact with a microbe
    in a nonliving reservoir

55
Patterns of Transmission in Communicable Diseases
Figure 13.11
56
Transmission
  • Contact transmission
  • Indirect transmission
  • Vehicle any inanimate material commonly used by
    humans that can transmit infectious agents (food,
    water, biological products, fomites)
  • Contaminated objects (doorknobs, telephones,
    etc.)
  • Food poisoning
  • Oral-fecal route
  • Air as a vehicle
  • Indoor air
  • Droplet nuclei
  • Aerosols

57
Figure 13.12
58
Nosocomial Infections The Hospital as a Source
of Disease
  • Nosocomial infections infectious diseases that
    are acquired or develop during a hospital stay
  • 2-4 million cases a year
  • The importance of medical asepsis

59
Figure 13.13
60
Universal Blood and Body Fluid Precautions
  • Universal precautions (UPs) guidelines from the
    Centers for Disease Control and Prevention
  • Assume that all patient specimens could harbor
    infectious agents
  • Include body substance isolation (BSI)techniques
    to be used in known cases of infection

61
Which Agent is the Cause? Using Kochs
Postulates to Determine Etiology
  • Etiology study of the cause of the disease
  • Etiologic agent the causative agent
  • Robert Koch developed a standard for
    determining causation that would stand the test
    of scientific scrutiny

62
Figure 13.14
63
Kochs Postulates
  • Find evidence of a particular microbe in every
    case of a disease
  • Isolate that microbe from an infected subject and
    cultivate it in pure culture in the laboratory
  • Inoculate a susceptible healthy subject with the
    laboratory isolate and observe the same resultant
    disease
  • Reisolate the agent from this subject

64
Epidemiology The Study of Disease in Populations
  • Epidemiology the study of the frequency and
    distribution of disease and other health-related
    factors in defined human populations
  • Involves not only microbiology but also anatomy,
    physiology, immunology, medicine, psychology,
    sociology, ecology, and statistics

65
Who, When, and Where? Tracking Disease in the
Population
  • Epidemiologists concerned with virulence, portals
    of entry and exit, and the course of the disease
  • Also interested in surveillance collecting,
    analyzing, and reporting data on the rates of
    occurrence, mortality, morbidity, and
    transmission of infections
  • Reportable diseases by law, must be reported to
    authorities
  • Centers for Disease Control and Prevention (CDC)
    in Atlanta, Georgia
  • Weekly notice the Morbidity and Mortality
    Report
  • http//www.cdc.gov/mmwr/
  • Shares statistics with the World Health
    Organization (WHO)

66
Epidemiological Statistics Frequency of Cases
  • Prevalence the total number of existing cases
    with respect to the entire population
  • Prevalence (total number of cases in population
    / total number of persons in population) x 100
  • Incidence the number of new cases over a
    certain time period
  • Incidence number of new cases / total number of
    susceptible persons
  • Mortality rate the total number of deaths in a
    population due to a certain disease
  • Morbidity rate the number of persons afflicted
    with infectious diseases

67
Figure 13.15
68
Figure 13.16
69
Current epidemiological data on H1N1
  • As of October 3, 2009, 99 of circulating
    influenza viruses in the United States were 2009
    H1N1 influenza.
  • Among people who become infected with 2009 H1N1,
    certain groups appear to be at increased risk of
    complications and may benefit most from early
    treatment with antiviral medications.
  • Based on currently available data, approximately
    70 of persons hospitalized with 2009 H1N1
    influenza have had a recognized high risk
    condition. These groups are similar to those who
    are at increased risk for seasonal
    influenza-related complications
  • Children younger than 2 years old
  • Adults 65 years of age or older
  • Pregnant women and women up to 2 weeks postpartum
    (including following pregnancy loss)
  • Persons with the following conditions
  • Chronic pulmonary (including asthma),
    cardiovascular (except hypertension), renal,
    hepatic, hematological (including sickle cell
    disease), or metabolic disorders (including
    diabetes mellitus)
  • Disorders that that can compromise respiratory
    function or the handling of respiratory
    secretions or that can increase the risk for
    aspiration (e.g., cognitive dysfunction, spinal
    cord injuries, seizure disorders, or other
    neuromuscular disorders)
  • Immunosuppression, including that caused by
    medications or by HIV
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