Download Infectious Diseases

INFECTIOUS
DISEASES
Chain of Infections
ORDER OF THE CHAIN
 Agent
 Reservoir
 Portal of exit
 Mode of transmission
 Portal of entry
 The new host
ORDER OF THE CHAIN
 Agent
 Reservoir
 Portal of exit
 Mode of Transmission
 Portal of entry
 The new host
AGENT
 The first link in the chain of infection is the disease causing agent
 This is the actual pathogen
 Example in the video: Influenza B
RESERVOIR
 Where it lives and thrives- must have a favorable environment to
survive
 In many of the most common diseases, the reservoirs are the bodies of
already infected people
 For other diseases, the reservoir could be animals (rabies) or non living
environments such as soil (tetanus)
 Example in the video: man in the elevator
PORTAL OF EXIT
 For agents to cause disease and illness, it is necessary that they leave
their reservoirs
 Example in the video: the respiratory system (sneeze)
 Principle portals of exit are:
 Digestive system
 Urinary system
 Respiratory system
 Reproductive system
 Blood
MODE OF TRANSMISSION
 This is the way that the
pathogen is passed from the
reservoir to a susceptible host
 How is it being transmitted
 Example in the video: air
droplets (airborne-inhalation of
infected particles)
 Two Principle Methods of
Transmission:
 Direct

Human to human

Droplet

Fecal-oral spread
 Indirect: occurs between infected and
uninfected people when infectious
agents travel by means of non human
objects

Inanimate objects (ex: water, food)

Vectors (ex: insects, birds, deer)

Airborne (ex: inhalation of infected
particles)
PORTAL OF ENTRY
 How the pathogen gets into the next person
 Four possible portals of entry:
 Digestive system
 Respiratory system
 Reproductive system
 Break in the skin
 Example in the video: respiratory system (inhalation of particles)
THE NEW HOST
 This is the new carrier
 Example in the video: Holly’s friend at the coffee shop who drank out of
her cup