Download Infectious Diseases

Infectious
Diseases
Dr. Wael H. Mansy, MD
Assistant Professor
College of Pharmacy
King Saud University
2009
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
The immune reaction of host
in infectious process will be :
Infection
and Immunity
Non specific
immunity
Humoral
Immunity
Immunoglobulin:
IgG, IgM, IgE, IgA, IgD
Barrier Action
Ext. barriers:
skin , mucosa &
their Secretion
Specific
immunity
Int. barriers:
Placenta or BBB
Phagocytosis
Humoral Action
Complement, Lysozyme,
Fibronectin, Cytokines
Cell mediated
immunity
Infectious Diseases
Barriers for Defense Against Infection:
1. Skin:

Prevents entry of infectious organisms, unless injured.

Severe burn patients who die are usually killed by infections. So much skin is
damaged they are very vulnerable to infections.
2. Mucus membrane:

Mucous is usually rich in enzymes that will kill many pathogens
3. Cilia:

These are hair-like structures lining the respiratory tract. They work to sweep
foreign particles out of the respiratory tract.

Damaged by smoking, leaving smokers more vulnerable to infections.
4. Coughing:

Helps remove foreign material from respiratory tract.
5. Personal Hygiene

Helps reduce the number of pathogenic organisms on the skin and other
surfaces of the body.
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
Fever:

Common symptoms and signs
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.
Mechanism of Fever

PGE2 acts on neurons in the preoptic area
(POA) through the prostaglandin E receptor
3 (EP3). EP3-expressing neurons in the POA
innervate
the
dorsomedial
hypothalamus
(DMH), the rostral raphe pallidus nucleus in
the
medulla
oblongata
paraventricular
hypothalamus .
nucleus
(rRPa)
(PVN)
and
the
of
the
Mechanism of Fever
Fever signals sent to the DMH and rRPa
lead to stimulation of the sympathetic
output system, which evokes nonshivering thermogenesis to produce body
heat and skin vasoconstriction to decrease
heat loss from the body surface.
 It is presumed that the innervation from
the POA to the PVN mediates the
neuroendocrine effects of fever through
the pathway involving pituitary gland and
various endocrine organs

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