مواضيع المحاضرة: Pathogens transmission of infectious agents Tissue response to infectious agent Suppurative inflammation Necrotizing inflammation Granulomatous inflammation Interstitial inflammation cytopathic-cytoproliferative response
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Infectious Diseases


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Definitions

disease

deviation in the normal structure or function 

of body organ or system

•Infection

Entry, establishment & multiplication of a 

microorganism in the body

•Infectious disease: 

disease caused by infectious agent

•Symptoms

: features of a disease that is felt by the patient.

•Signs

: features or manifestations of a disease that is 

observed by the doctor.

•Clinical features

: symptoms & signs of a disease


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Incubation period

: time interval between onset of infection 

& appearance of symptoms.

host

: organism that harbor & nourish another organism 

(parasite)

Carrier

: A person or animal with asymptomatic infection that 

can be transmitted to another person or animal. 

Pathogen

: A microorganism capable of causing disease.

Pathogenicity

: ability of infectious agent to cause disease


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Toxigenicity

: ability of a microorganism to produce a toxin. 

Opportunistic pathogen

: microorganism that cause a disease 

only when the host's resistance is impaired.

Virulence

: quantitative ability of an agent to cause disease. 

Virulence involves invasiveness & toxigenicity 

Invasiveness

: process by which microorganisms enter & 

spread in the body


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Mode of transmission of infectious agents

• I

ngestion: e.g., Typhoid

• I

nhalation: e.g., infleunza

• I

noculation: e.g., malaria

Infectious agents

(Prions, Viruses, Chlamydia, Mycoplasma, Bacteria,

Fungi, Protozoa, Helminthes)


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Prions

•An infectious protein particle without nucleic acid.

•Obligate intracellular agents

•Resistant to common disinfectant e.g., ethanol, 
, but susceptible to household bleach & iodine

•Causes kuru, Crutzfeldt-Jacob & bovine spongiform 

encephalitis


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Viruses

• Are obligate intracellular agents

• Contain DNA or RNA within a cylindrical or spherical 

protein coat (capsid), which may be surrounded by
lipid envelope.

• Viral infection can cause:
1. Acute illness (e.g., common cold, infleunza etc)
2. Chronic disease (e.g., AIDS)
3. Latent infection with occasional re-activation 

e.g., Herpse viruses


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Bacteria

•Simple cell (prokaryotic: Karyo- = nucleus) w/o true nucleus

i.e., chromosomes not surrounded by nuclear membrane

•Divided into 2 main groups according to Gram stain reaction 

(Gram positive bacteria looks purple-violet or Gram negative 

deep pink)

•Extracellular like streptococci or intracellular like 

mycobacterium tuberculosis


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Chlamydia, Rickettsiae and 
Mycoplasmas

Are similar to bacteria  but lack certain structures (a cell wall-
mycoplasma) or metabolic capabilities (ATP synthesis-
chlamydia)

Chlamydia cause genitourinary infections, conjunctivitis, and 
or respiratory infections of newborns.

Rickettsia are transmitted by insect vectors, including lice, 
tick, and mites and causes hemorrhagic vasculitis, 
pneumonia, hepatitis and encephalitis.

Mycoplasma bind to the surface of epithelial cells and cause 
atypical pneumonia or urethritis


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Fungi

•Eukaryotic (has true nucleus, mitochondria like 
human cells)

•Cause superficial infection (e.g., candida) or deep 

infection in immune  compromized persons as in 

AIDS patients


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Protozoa

•Single celled eukaryotic organisms.
•Trichomonas vaginalis transmitted sexually
•Entamoeba histolytica & Giardia lamblia transmitted

by ingestion 

•Plasmodium & leishmania transmitted by insect


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Helminthes

- Are highly differentiated multicellular 

organisms with complex life cycles.

-

Cause disease in proportion to the 
number of infecting organisms

-

Roundworms, hookworms, flatworms.


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Tissue response to infectious agent

1.Suppurative inflammation

2.Necrotizing inflammation

3.Granulomatous inflammation

4.Interstitial inflammation

5.cytopathic-cytoproliferative response


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Suppurative inflammation:

Acute inflammatory response 

with neutrophil infiltration, & purulant exudate.

Typically seen in pyogenic bacterial infections 
e.g., Staphylococci & streptococci (bacterial 
meningitis, Bacterial pneumonia) 


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Necrotizing inflammation

Virulent organism producing sever tissue damage 
and extensive cell death  e.g.(Necrotizing 
fasciitis , Necrotizing pharyngitis)


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Granulomatous inflammation

* Granulomatous response 

predominates

* Slow- growing organisms

- Mycobacteria

-Fungi

- Parasites


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Interstitial inflammation

- Diffuse mononuclear interstitial infiltrate

- As in interstitial lung disease can caused by 
long term exposure to hazardous materials 
such as asbestos.

And autoimmune disease as rheumatoid 

arthritis or even viral infection as myocarditis 
, hepatitis and others.


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Cytopathic-cytoproliferative response

Structural changes in host cells that are caused 
by viral invasion.

Characterized by virus induced damage to 
individual 

host cells with little or no inflammatory 
response

May show inclusion bodies (intranuclear or 
cytoplasmic 

aggregate of viral components or blisters 

(e.g., herpse viruses) or apoptosis (as in viral 
hepatitis) 


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Thank you




رفعت المحاضرة من قبل: Bahaa
المشاهدات: لقد قام 4 أعضاء و 140 زائراً بقراءة هذه المحاضرة








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