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GENERAL PATHOLOGY OF INFECTIOUS DISEASES

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GENERAL PATHOLOGY OF INFECTIOUS DISEASES * * * * * * Infectious Diseases Are disorders in which tissue damage or dysfunction is produced by a micro-organism ... – PowerPoint PPT presentation

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Title: GENERAL PATHOLOGY OF INFECTIOUS DISEASES


1
GENERAL PATHOLOGY OF INFECTIOUS DISEASES
2
Infectious Diseases
  • Are disorders in which tissue damage or
    dysfunction is produced by a micro-organism
  • Classified as
  • Contagious (person to person)
  • Non-contagious acquired from
  • -Exogenous sources such as animals, insects,
    soil, air
  • -or originating from endogenous microbial flora
    of the body

3
Factors That Influence The Development Of Disease
4
1-Host factors in infection
  • Inherited differences in response to infecting
    agents
  • Effects of age on response to infection
  • Effects of behavior on infection
  • Effects of the condition of the host defenses on
    infection

5
2-Virulence
  • Is the capacity of an organism to achieve
    infection
  • The organism must
  • 1-Gain access (enter) to the body
  • 2-Avoid the host defenses
  • 3-Accommodate to growth (be able to grow) in the
    human environment
  • 4-Parasitize (live on) human resources

6
Host Defense Mechanisms
  1. Skin
  2. Tears
  3. Normal bacterial flora
  4. Gastric acid
  5. Bile
  6. Salivary and pancreatic secretions
  7. Mucociliary blanket
  8. Secretions e.g. bronchial secretion
  9. Immune system (e.g. neutrophils, monocytes)

7
Host Factors In Infection
  • An infectious agent may
  • Fail to infect some persons
  • Produce asymptomatic infections
  • Cause symptomatic disease
  • Produce lethal (deadly) infection

8
Effect of age on response to infection
  • -The age of the host affects the outcome of
    exposure to many infectious agents
  • 1-Some organisms produce more severe disease in
    utero than in children or adults (e.g. German
    Measles)

9
  • 2-Tuberculosis in children lt 3 y ? more severe
    due to immaturity of the immune system)
  • 3-The elderly ? (common respiratory illnesses are
    more often fatal in persons over 65 y)

10
How Infectious Agents Can Cause Disease
  • 1-They can contact or enter host cells and
    directly cause cell death
  • 2-They can release
  • a)Endotoxins or exotoxins that kill cells
  • b)Enzymes that degrade tissue components
  • 3)They can induce host cell responses that cause
    tissue damage usually by immune-mediated
    mechanisms

11
BACTERIAL INFECTION
12
Bacteria Induced Injury Depends On
  • Damage to host cells depends on the ability of
    bacteria to adhere to and enter host cells or to
    deliver toxins

13
Mechanism Of Bacterial Injury
  • Production of toxins
  • a) Endotoxins
  • b) Exotoxins
  • Hypersensitivity reaction causing tissue injury
    i.e. the immune response to infection
  • Tissue invasion by microbes

14
Bacterial Endotoxins
  • A lipopolysaccharide (LPS) - a structural
    component of the outer cell wall of gram negative
    bacteria
  • Biologic effects of endo-toxins
  • Induction of fever
  • Septic shock
  • Disseminated intravascular coagulation (DIC)
  • Acute respiratory distress syndrome (ARDS)
  • Effects on the cells of the immune system

15
Bacterial Exotoxins
  • Are secreted proteins that directly cause cell
    injury and disease manifestations
  • Examples of bacteria that secrete exotoxins
  • Diphtheria bacteria
  • Bacillus anthraces

16
INFLAMMATORY RESPONSE TO INFECTIOUS AGENTS
17
Effects of bacterial infection
  • Cell injury ? necrosis and degeneration
  • Inflammation acute or chronic
  • Blood invasion by bacteria or its products
    leading to either
  • Bacteraemia
  • Toxaemia
  • Septicaemia
  • Pyaemia

18
Bacteraemia
  • Transient invasion of the blood with bacteria
    without significant toxaemia
  • Examples
  • After tooth extraction
  • Blood spread from a septic focus as tonsillitis

19
Toxaemia
  • This is the circulation of bacterial toxins
    leading to harmful effects
  • Types
  • Acute toxemia e.g. typhoid fever diphtheria
  • Chronic toxemia e.g. lung abscess T.B. disease

20
Septicaemia
  • A serious fatal condition in which large numbers
    of virulent bacteria circulate and multiply in
    the blood accompanied by severe toxemia

21
Pyaemia
  • Development of small abscesses (pyaemic abscess)
    within one or more organ causes by circulating
    septic emboli. The condition is commonly fatal

22
Opportunistic Infections
23
Opportunistic Infections (OI)
  • Infections with pathogenic micro-organisms which
    occur in persons with advanced immunodeficiency

24
Opportunistic Infection classifications
  1. Fungal infections
  2. Bacterial infections
  3. Viral infections
  4. Protozoal infections

25
Fungal Opportunistic Infections
  • Candidiasis
  • Pneumocystis carinii pneumonia (PcP)
  • Aspergillosis
  • Cryptococcosis

26
Bacterial Opportunistic Infections
  • Recurrent bacterial pneumonia
  • Progressive Tuberculosis

27
Viral Opportunistic Infections
  • Herpes viruses
  • Cytomegalovirus (CMV)

28
Protozoal Opportunistic Infections
  • Toxoplasmosis
  • Giardiasis

29
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