Transcript 2_Factors in the Spread of Disease

FACTORS IN THE SPREAD
OF DISEASE
Spread of Diseases

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There have been
several diseases that
have spread across the
world killing many
In the middle ages it
was the Bubonic or
Black Plague
In 1981 it was HIV
Epidemiology

An area of investigation that deals with factors that
influence the frequency and distribution of diseases
 Find
ways to control and prevent the outbreak of
disease
 Look for the source of transmission
 Reporting of the control of the disease
Patterns of Disease Occurrence

Incidence or Prevalence
 The
number of new cases seen in a specific time period
 Morbidity Rate
 The
number of new cases per 10,000 in the population per
year
 Mortality
 Refers
Rate
to the number of individuals that died as a result of a
specific disease in a specific time period
Endemic, Epidemic, Pandemic and
Sporadic Disease Patterns

Endemic Disease
A
disease that is constantly present in the population of
a particular geographic area, but involves relative few
individuals
 Severity
of the disease is low
 Does not present as a major public health problem

Tuberculosis, mumps, the STD chancroid and gonorrhea
Endemic, Epidemic, Pandemic and
Sporadic Disease Patterns

Epidemic
 An
unusual occurrence of a disease involving large
segments of a population for a limited period of time
 An endemic disease can develop into an epidemic if a
harmful form of the pathogen appears
 Influenza
and measles are good examples
 Genital Herpes and Genital Warps are in epidemic
proportions
Endemic, Epidemic, Pandemic and
Sporadic Disease Patterns

Pandemic
A
series of epidemics
affecting several
countries, or even
major portions of the
world
 Influenza
of 1918-
1919
 HIV and AIDs are
following a similar
pattern
Endemic, Epidemic, Pandemic and
Sporadic Disease Patterns

Sporadic Diseases
 Are
uncommon, occur
irregularly and affect
only a relatively few
persons
 Diptheria
 Whooping
Cough –
although this is on the
rise in the US

Transmission Factors
include:
 Sources
and reservoirs
of disease agents
 Portals by which the
agents leave and enter
the body
 The mechanisms or
means of transmission
Factors in the Spread of Infectious
Diseases

Reservoirs of Infection
A
host or local environment that supports the survival
and multiplication of pathogens is referred to as a
reservoir of infection
 Living reservoirs include infected humans and other
animals
 Nonliving reservoirs include air, food, soil, water, eating
utensils and toothbrushes
 Provides the disease agent a suitable environment to
survive for prolonged periods
Factors in the Spread of Infectious
Diseases

Carrier
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Healthy Carrier
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The individual who is in an incubating state, undergoing the
initial stages of a disease without exhibiting symptoms
Intermittent Carrier

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A carrier with no apparent ill effects
Incubatory Carrier


Individuals who harbor pathogens transmissible to others
Periodically releases disease agents
Convalescent Carrier

Serves as a source of pathogens during the recovery period
How do Pathogens Get Into and Out of
the Body?

Portals of Entry
 Pathogens
enter the body through a small number or
routes
 Skin
 Respiratory
system
 Gastrointestinal system
 Genitourinary system
 Wounds
 Animal bites

Particular pathogens are generally restricted to a
specific portal of entry
Portal of Entry

Infectious Dose
 The
number of pathogens needed to initiate a disease
process
 May
be as low of one organism or may need hundreds of
thousands


HIV infection requires large doses of disease agent
The pathogen must overcome the hosts defenses in
order to enter
 If
it cannot overcome the defenses the pathogen dies
Portals of Exit

The site at which the organisms leave the body
 Pathogens
are typically discharged with body fluids
and wastes.
 Respiratory pathogens exit by
 Coughing
 Sneezing
 Speaking
 STDs
such as gonorrhea and HIV discharge through
semen and vaginal secretions
Mechanisms of Disease Transmission

Transmission may occur by:
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Direct contact with infected
person or carrier
Indirect contact with
nonliving objects, or food
or water contaminated by
infected individuals
Inhalation of airborne
dust or droplets of saliva,
or other body fluids
containing pathogens
Injection of body fluids
containing disease agents
Insects and related forms
carrying pathogens
Contact Transmission

Direct Contact


Refers to the transmission
of pathogens from
person to person through
close personal
association
Coughing
 Sneezing
 Handshaking
 Kissing
 Sneezing

Indirect Contact


Infectious agents are
carried form one
individual to another on
contaminated, living or
nonliving objects
Fomites

Contaminated nonliving
objects other than food
and water
Hypodermic needle
 Toothbrush
 Eating utensils

Mechanical Transmission

Transmission where situations involving the physical
carrying of pathogens on or within contaminated
materials such as food, water or insects
 Five
F’s
 Food
 Fingers
 Flies
 Feces
 Fomites
Mechanical Transmission
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Vector

Forms of life that transmit disease to humans
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Mechanical Vectors
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Flies
Ticks
Cockroaches
Mosquitoes
Transmitters that carry infectious agents on their bodies and are not used
by the agents for multiplication
Biological Vectors

Serves as reservoirs and are at times required by disease agents for
their development
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
Ticks
Mosquitoes
There are no known STDs transmitted by arthropod vectors
Biological Transmission

A portion of the pathogen’s development occurs in the
form of life that serves to transmit the disease agent
Injection of blood
 Blood products
 Bites of warm-blooded animals
 Arthropods
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Malaria
 Rabies
 Hepatitis
 HIV
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Horizontal and Vertical Transmission

Horizontal Transmission
 Transfer
of disease agents in the population by air,
physical contact, food, water or vectors

Vertical Transmission
 Transfer
of infectious agents from parent to offspring
by means of male and female sex cells or breast milk
or during pregnancy
 Syphilis
and HIV
General Approaches to the Control of
Contagious Diseases

Isolation and Quarantine
 Prevents
contact with the general population
 Minimizes
the spread of the disease
 Protects infected individual from exposure to other diseases

Elimination of Vectors and Sources of Disease
Agents
 Hand
washing
 Disinfectant
 Insecticides
Immunization
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Vaccination for the prevention of diseases
Builds resistance to the disease
Large spread controversy today
The signs of certain sexually transmitted diseases
(STDs) such as syphilis and chlamydial infection are
not always obvious
A.
B.
True
False
In general, STDs can be acquired through casual
contact situations such as shaking hands.
A.
B.
True
False
Diagnostic tests are available for the
detection of most STDs.
A.
B.
True
False
Most STDs are treatable if detected
early.
A.
B.
True
False
Having an STD such as syphilis, chancroid, or genital
wars can increase the possibility of human
immunodeficiency (HIV) transmission.
A.
B.
True
False
The proper use of latex condoms during sexually
related activities, while not foolproof, is effective in
preventing STD transmission.
A.
B.
True
False
An infected mother can transmit certain STDs such
as syphilis and HIV infection to her newborn.
A.
B.
True
False
With the exception of hepatitis B virus infection, no
immunization (vaccines) are available for any STD.
A.
B.
True
False
The use of oil-based lubricants such as Crisco and
Vaseline can weaken condoms, making them useless as
protection against STD transmission
A.
B.
True
False
Sexually transmitted diseases can
spread by women as well as men.
A.
B.
True
False
An individual can acquire an STD by
donating blood.
A.
B.
True
False
Sexually transmitted diseases such as syphilis
and gonorrhea can be spread by kissing.
A.
B.
True
False