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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
1. What is an infectious disease??
2. What is an infection??
3. Causes of re-emerging of the problem of the infectious diseases
4. Microbiological Classification of Infectious Diseases.
5. Means of Transmission of Infectious Diseases.
6. The action of pathogen in infectious process (pathogenicity)
7. What is infectivity ,virulence, Immunogenicity and incubation period .
8. Manifestations of infectious process (Infection spectrum).
9. The immune reaction of host in infectious process.
10. Common symptoms and signs.
Infectious Diseases
What is an infectious diseases??
Infectious disease is:
①
A group of common diseases
②
Caused by different pathogens
③
Possessing infectivity.
④
To form epidemic.
⑤
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
①
Complex process of interaction between pathogen
and human body
②
Infection is composed of three factors: pathogen,
host and environment
③
There are commensalisms and opportunistic
infection
Infectious Diseases
Causes of re-emerging of the problem of the infectious diseases:
1. Loss of Antibiotic Effectiveness.
2. Increased Population Density: Transmission from person to person is more likely.
3. Travel: Travelers may bring back pathogens.
4. Global Warming: May affect rainfall or other factors that currently affect diseases
or their carriers.
5. Biological Warfare or Terrorist Attacks: There have recently been a number of
threats of such attacks involving anthrax.
6. New Routes of transmission: Organ Transplants.
7. Complacency and Ignorance: Many, possibly most, people do not wash their hands
after using the toilet.
Microbiological Classification of Infectious
Diseases
Bacterial
Viral
Fungal
Parasitic
Gram-negative
Gram-positive
DNA virus
RNA virus
Enveloped vs non-enveloped
Disseminated
Localized
Protozoa
Helminths
Means of Transmission of Infectious
Diseases
Contact
Requires direct or indirect contact (fomite,
blood, or body fluid)
Food or
Water
Ingestion of contaminated food or water
Airborne
Inhalation of contaminated air
Vector-borne Dependent on biology of vector as well as
infectivity of organism
Perinatal
Sexual
Similar to contact infection, however, the
contact may occur in utero or during delivery.
transmission by sexual intercourse.
Factors Influencing Disease Transmission
Agent
Environment
• Infectivity
• Weather
• Pathogenicity
• Housing
• Virulence
• Geography
• Immunogenicity
• Occupational setting
• Antigenic stability
• Air quality
• Survival
• Food
• Age
Host • Sex
• Genotype
• Behaviour
• Nutritional status
•Health status
Infectious Diseases
Factors Influencing Disease Transmission( Agent)
Pathogenicity
What does pathogenicity mean???
It means the ability of a microbiological agent to induce
disease
The pathogenicity of pathogen is related to :
1.
Invasiveness
2.
virulent
3.
Number of pathogen
4.
Mutation (variability)
Infectious Diseases
Factors Influencing Disease Transmission( Agent)
Infectivity:
 Ability
of agent to cause infection
 Number
 In
of infectious particles required
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)
Immunogenicity
 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
Infectious Diseases
Infection and Immunity
Manifestations of infectious process (Infection spectrum):
1) Clearance of pathogen (no infection)
2) Covert infection (subclinical infection)
3) Overt infection (Clinical infection or apparent infection)
4) 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
5) Latent infection.
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
Transmission
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
T
S
Susceptible
Immune
Sub-clinical
Clinical
P
S
S
T
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
*Influenza
*AIDS/HIV
*Herpes (Simplex and Zoster)
*Hepatitis A,B,C, D, E, F and G.
*Measles, Mumps and Rubella.
*Poliomyelitis.
*Infectious mononucleosis.
Fungi
*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
-mushrooms.
*Can cause disease by releasing enzymes that damage cells or by
producing toxins. Some mushrooms produce VERY deadly toxins.
Fungal Diseases
-Candidiasis.
-Athlete’s foot - Tinea pedis
-Jock itch - Tinea cruris
-Nail fungus - Tineu unguis
-Ringworm
-Histoplasmosis
-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.
Infectious Diseases
Common symptoms and signs
Fever:
 Three stages : effervescence
fastigium
deffervescence

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
• 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 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.
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.
*Petechia:
*Vesiculo-pustular rash
*Urtecaria.
Enanthema
Infectious Diseases
Common symptoms and signs
 Toxemic symptoms
 Mononuclear phagocyte system reactions
Hepato- splenomegaly
Lymph nodes enlargement
 Clinical types
acute, sub acute, mild, common, severe, fulminant,
typical, atypical, abortive, ambulatory