Download Set 5 Transmission

Emerging Diseases
Lecture 5:
Disease Transmission
5.1 Overview
5.2: Routes of Transmission
5.3: Summary
5.1: Overview
The Germ Theory explains infectious diseases.
They pass from person to persondirectly or indirectly through the
environment.
How does this happen?
Overview: Disease Transmission
• The “route of infection” is the way the disease
moves from one individual to another
• The disease enters the body through a “portal of
entry”.
• Different diseases are characterized by different
routes of infection
• Some pathogens (disease-causing agents) utilize
more than one route
• To attack your body, the pathogen must attach to
a molecule on the surface of your cells called a
“disease receptor”
To stop a pathogen you
have to block its route of
transmission.
This is called “breaking
the chain of infection”.
5.2: Routes of Transmission
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Gastrointestinal
Respiratory
Direct Contact
Body fluids
Vector
They are not always clear-cut: sometimes they overlap
Gastrointestinal Route
• Also known as: fecal-oral, food-borne or waterborne, alimentary
• Disease agent enters with contaminated food or
water
• Examples: typhoid, polio, Salmonella, E. coli
O157:H7, many parasitic diseases
• Raw or undercooked food is usually the problem
• Beaver Valley Mall outbreak of hepatitis A is the
classic example in Pennsylvania
Hepatitis A Outbreak Beaver Valley Mall
• 660 cases and 4 deaths Oct-Nov. 2003
• Largest Hepatitis Outbreak in State History
• Health officials issued an alert yesterday, warning the estimated 11,000
customers who ate at the Beaver Valley Mall Chi-Chi's between October
22nd and November 2nd that they may have been exposed to Hepatitis A,
and should get immunized as a precaution.
January 9, 2004
Bill Vidonic, Times Staff Writer
BEAVER - Richard Miller will be on antirejection medication for the rest of his
life to keep his new liver functioning
properly.
The 57-year-old said he is struggling to
regain the stamina he lost after a liver
transplant on Nov. 8, a life-saving
procedure made necessary when he
contracted hepatitis A after eating at the
Chi-Chi's Mexican restaurant in Center
Township.
"I lost my liver for no reason at all,"
Miller said from his Beaver home
Thursday.
What conditions favor the spread of
gastrointestinal disease?
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Garbage
Sewage
Bad sanitation
Contaminated water
No refrigeration
Hot weather
Others?
Respiratory Route
• Pathogen enters via breathing or via contact
with the respiratory system
• Smallpox, influenza, measles, many bacterial
pathogens
• Inhalation of dust or aerosols
• Irritation of respiratory system leads to
sneezing-droplets carry germs
This is a great way to transmit disease
What conditions favor the spread of
respiratory disease?
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Crowded living conditions
Dirty clothes and bedding
Cold weather
Others?
Direct Contact
Fomites
Pathogens may
contaminate inanimate
objects from which a
healthy person gets the
disease: the objects are
called fomites.
What conditions favor the spread of
direct contact disease?
• Public facilities not clean
• Improper hand-washing
• Others?
Transmission via Body Fluids
(not inhaled)
• “blood-borne”: Hepatitis B, HIV-1 and HIV-2
• “sexually-transmitted” or “STDs” or
“urogenital”: Hepatitis B, HIV-1 and HIV-2,
syphilis, gonorrhea, chlamydia
• Herpes viruses like Epstein-Barr Virus can be
transmitted through saliva (“mono” or “kissing
disease”)
What conditions favor the spread of
diseases in body fluids?
• Behavior
• Others?
Vector Transmission
The disease is carried from person to person
by an animal:
Usually an insect or close relative such as a
tick.
The carrier animal is called a “vector”.
Often, there are host species in addition to
humans. These are called “reservoir”
species or “reservoir” hosts.
Malaria is the best example of a vector-borne disease. In Pennsylvania, two
Important vector-borne diseases are West Nile (virus) and Lyme Disease
(bacterial-caused by Borrelia burgdorferi).
What conditions favor the spread of
vector-borne disease?
• Climate change
• Habitat disruption
• Others?
More terms
• Some pathogens live peacefully on or in your
body until it weakens-then they attack. These
are called “opportunistic” pathogens.
• Diseases acquired from animals are called
“zoonotic”.
• Diseases acquired as a result of a medical
procedure are “iatrogenic”.
• Diseases acquired in a hospital are
“nosocomial”.
5.3: Summary-Five Important
Routes of Infection
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Gastrointestinal: food-borne or water-borne
Respiratory: air borne, most dangerous
Direct Contact: common
Body fluids: easy to stop
Vector: complex because additional species
involved