GENERAL PATHOLOGY OF INFECTIOUS DISEASES

1
GENERAL PATHOLOGY OFINFECTIOUS 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 TheDevelopment 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 CauseDisease

• 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 TOINFECTIOUS 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
THANK YOU