Upload
audra-ellis
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
Emerging Diseases
Lecture 5: Disease Transmission
5.1 Overview5.2: Routes of Transmission
5.3: Summary
5.1: OverviewThe Germ Theory explains infectious diseases.
They pass from person to person-directly 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
• 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 water-borne, 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 WriterBEAVER - Richard Miller will be on anti-rejection 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?
• 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
What conditions favor the spread of respiratory disease?
• Crowded living conditions• Dirty clothes and bedding• Cold weather• Others?
Pathogens may contaminate inanimate objects from which a healthy person gets the disease: the objects are called fomites.
Fomites
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 direct contact disease?
• Public facilities not clean• Improper hand-washing • 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, twoImportant 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”.