1. 5.2: Routes of Transmission
Emerging Diseases
Lecture 5:
Disease Transmission
5.1 Overview
5.2: Routes of Transmission
5.3: Summary

2. The Germ Theory explains infectious diseases.
5.1: Overview
The Germ Theory explains infectious diseases.
They pass from person to person-
directly or indirectly through the environment.
How does this happen?

3. 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”

4. To stop a pathogen you have to block its route of transmission.
This is called “breaking the chain of infection”.

5. 5.2: Routes of Transmission
Gastrointestinal
Respiratory
Direct Contact
Body fluids
Vector
They are not always clear-cut: sometimes they overlap

6. 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

7. 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 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.

8. What conditions favor the spread of gastrointestinal disease?
Garbage
Sewage
Bad sanitation
Contaminated water
No refrigeration
Hot weather
Others?

9. 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

10. This is a great way to transmit disease

11. What conditions favor the spread of respiratory disease?
Crowded living conditions
Dirty clothes and bedding
Cold weather
Others?

12. Direct Contact

13. Fomites
Pathogens may contaminate inanimate objects from which a healthy person gets the disease: the objects are called fomites.

14. What conditions favor the spread of direct contact disease?
Public facilities not clean
Improper hand-washing
Others?

15. 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”)

16. What conditions favor the spread of diseases in body fluids?
Behavior
Others?

17. 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).

18. What conditions favor the spread of vector-borne disease?
Climate change
Habitat disruption
Others?

19. 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”.

20. 5.3: Summary-Five Important Routes of Infection
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