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Infectious Diseases. Dr. Wael H. Mansy , MD Assistant Professor College of Pharmacy King Saud University. Infectious Diseases. Study Objectives : to know. What is an infectious disease?? What is an infection?? Causes of re-emerging of the problem of the infectious diseases

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Infectious Diseases

Dr. Wael H. Mansy, MD

Assistant Professor

College of Pharmacy

King Saud University


Infectious Diseases

Study Objectives: to know

  • What is an infectious disease??
  • What is an infection??
  • Causes of re-emerging of the problem of the infectious diseases
  • Microbiological Classification of Infectious Diseases.
  • Means of Transmission of Infectious Diseases.
  • The action of pathogen in infectious process (pathogenicity)
  • What is infectivity ,virulence, Immunogenicity and incubation period .
  • Manifestations of infectious process (Infection spectrum).
  • The immune reaction of host in infectious process.
  • Common symptoms and signs.

Infectious Diseases

What is an infectious diseases??

Infectious disease is:

A group of common diseases

Caused by different pathogens

Possessing infectivity.

To form epidemic.

Infectious disease is a threat to the health of people.


Infectious Diseases

What is an infectious disease??

A case is a risk factor …

  • Infection in one person can be transmitted to others

Infectious Diseases

What is an infection??

Definition of infection

Complex process of interaction between pathogen and human body

Infection is composed of three factors: pathogen, host and environment

There are commensalisms and opportunistic infection

causes of re emerging of the problem of the infectious diseases
Causes of re-emerging of the problem of the infectious diseases:

Infectious Diseases

  • Loss of Antibiotic Effectiveness.
  • Increased Population Density: Transmission from person to person is more likely.
  • Travel: Travelers may bring back pathogens.
  • Global Warming: May affect rainfall or other factors that currently affect diseases or their carriers.
  • Biological Warfare or Terrorist Attacks: There have recently been a number of threats of such attacks involving anthrax.
  • New Routes of transmission: Organ Transplants.
  • Complacency and Ignorance: Many, possibly most, people do not wash their hands after using the toilet.



  • Infectivity
  • Pathogenicity
  • Virulence
  • Immunogenicity
  • Antigenic stability
  • Survival
  • Weather
  • Housing
  • Geography
  • Occupational setting
  • Air quality
  • Food
  • Age
  • Sex
  • Genotype
  • Behaviour
  • Nutritional status
  • Health status


Factors Influencing Disease Transmission


Infectious Diseases

Factors Influencing Disease Transmission( Agent)


What does pathogenicity mean???

  • It means the ability of a microbiological agent to induce disease

The pathogenicity of pathogen is related to :



Number of pathogen

Mutation (variability)


Infectious Diseases

Factors Influencing Disease Transmission( Agent)


  • Ability of agent to cause infection
  • Number of infectious particles required
  • In person-to-person transmission, secondary attack rate is a measure of infectivity

Virulence :

  • Severity of the disease after infection occurs.
  • Measured by case fatality rate or proportion of clinical cases that develop severe disease.

Infectious Diseases


Factors Influencing Disease Transmission( Agent)

  • Ability of an organism to produce an immune response that provides protection against reinfection with the same or similar agent
  • Can be life long or for limited periods
  • Important information for development of vaccines
infection and immunity

Infectious Diseases

Infection and Immunity

Manifestations of infectious process (Infection spectrum):

  • Clearance of pathogen (no infection)
  • Covert infection (subclinical infection)
  • Overt infection (Clinical infection or apparent infection)
  • Carrier states
    • Health carrier after covert infection.
    • Convalescent carrier after overt infection.
    • Incubatory carrier before onset of disease.

According to carrier time : #acute (transient) carrier

#chronic carrier

  • Latent infection.
pathogenetic mechanisms

Infectious Diseases

Pathogenetic Mechanisms:
  • Direct tissue invasion: like smallpox
  • Production of a toxin: anthrax produce toxins that invade and destroy tissue
  • Immunologic enhancement or allergic reaction
  • Persistent or latent infection
  • Enhancement of host susceptibility to drugs
  • Immune suppression

Infectious Diseases












  • Cases
  • Index – the first case identified
  • Primary – the case that brings the infection into a population
  • Secondary – infected by a primary case
  • Tertiary – infected by a secondary case
incubation period

Infectious Diseases

Incubation period
  • Time between exposure and onset of symptoms or signs of infection.
  • Each disease has typical incubation period but varies widely.
  • Requires replication of the organism to some threshold level for producing symptoms

Bacterial Diseases

  • Tuberculosis
  • Scarlet Fever
  • tetanus
  • Gonorrhea
  • Diptheria
  • Streptococcal Infections
  • Pneumonia (can also be viral or fungal)
  • Pertussis
  • Bubonic Plague
  • There are many others.

Viral Diseases

*Common Cold



*Herpes (Simplex and Zoster)

*Hepatitis A,B,C, D, E, F and G.

*Measles, Mumps and Rubella.


*Infectious mononucleosis.


*Organisms, but without chlorophyll

*Generally life off of dead organisms or dead material within a living organism.

*Some are single cell organisms (yeast)

*Some are multi-cell organisms (mushrooms)

*Many are extremely valuable:

-yeasts give us bread and alcohol


*Can cause disease by releasing enzymes that damage cells or by producing toxins. Some mushrooms produce VERY deadly toxins.


fungal diseases
Fungal Diseases


-Athlete’s foot - Tineapedis

-Jock itch - Tineacruris

-Nail fungus - Tineu unguis



-Over-the-counter medications are usually effective for mild infections, except of the nails.

-Systemic treatments can be prescribed for serious infections, including the nails, and for histoplasmosis.

common symptoms and signs

Infectious Diseases

Common symptoms and signs


  • Three stages : effervescence



  • Five kinds of fever:

*Sustained fever.

*Remittent fever: one that shows significant variations in 24 hours but without return to normal temperature. ,

*Intermittent fever: an attack of malaria or other fever, with recurring fever episodes separated by times of normal temperature ,

*Relapsing fever: alternating periods of fever and apyrexia, each lasting from five to seven days.

*Saddle type fever.

*Irregular fever.

mechanism of fever
Mechanism of Fever
  • Temperature is ultimately regulated in the hypothalamus. A trigger of the fever, called a pyrogen, causes a release of prostaglandin E2 (PGE2). PGE2 then in turn acts on the hypothalamus, which generates a systemic response back to the rest of the body, causing heat-creating effects to match a new temperature level.
mechanism of fever1
Mechanism of Fever
  • A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous) to the body.
  • The bacterial substance lipopolysaccharide (LPS), present in the cell wall of some bacteria, is an example of an exogenous pyrogen.
  • Cytokines (especially interleukin 1) are a part of the innate immune system, are produced by phagocytic cells, and cause the increase in the thermoregulatory set-point in the hypothalamus. Other examples of endogenous pyrogens are interleukin 6 (IL-6), and tumor necrosis factor-alpha.
common symptoms and signs1

Infectious Diseases

Common symptoms and signs

Rash eruption

Date of eruption

1st: chickenpox 2nd: scarlet fever

3rd: smallpox 4th: measles

5th: typhus 6th: typhoid fever

Location of eruption

Form of rash

Exanthema :

*maculo-papular rash: A maculopapular rash is a flat, red area on the skin that is covered with small confluent bumps e.g. measles.


*Vesiculo-pustular rash



Toxemic symptoms

Mononuclear phagocyte system reactions

Hepato- splenomegaly

Lymph nodes enlargement

Clinical types

acute, sub acute, mild, common, severe, fulminant, typical, atypical, abortive, ambulatory

Infectious Diseases

Common symptoms and signs