Infectious Diseases
Presented by: M. Alvarez
Adapted from:M. Arias, C. Goedhart,
and M.Burke
What is an Infection?
A harmful invasion and spread of foreign species,
or pathogen, in a host.
VIRUS
 Small pox, measles, influenza, Ebola
PRIONS
Cow’s disease
BACTERIA
Tuberculosis, pneumonia, salmonella, anthrax
FUNGUS
Athlete’s foot, ring worm
PROTISTS
Malaria, toxoplasmosis, Algae
Infectious Agents
Worldwide mortality due to
infectious diseases
Estimated number of people in the
world living with HIV/AIDS in 2008
Spread of Disease & Transmission
Infection in one person can be transmitted to others
T
S
Susceptible
Immune
Sub-clinical
P
S
S
T
Clinical
Cases
 Patient “Zero” – the first case identified
 Primary – the case that brings the infection into a population
 Secondary – infected by a primary case
 Tertiary – infected by a secondary case
Transmission of Pathogens
•Direct contact
•Indirect contacts
•Air
•Objects
•Vectors
Routes of transmission
Direct
Indirect
 Skin-skin
 Herpes type 1
 Mucous-mucous
 Food-borne
 STI
 Across placenta
 toxoplasmosis
 Through breast milk
 Salmonella
 Water-borne
 Hepatitis A
 Air-borne
 Chickenpox
 HIV
 Sneeze-cough
 Influenza
Vector
 A carrier of an infectious agent
Ex. Malaria Parasite carried
by Mosquito
Factors Influencing Disease
Transmission
Agent
Environment
• Weather
• Infectivity
• Housing
• Pathogenicity
• Geography
• Virulence
• Occupational setting
• Antigenic stability
• Air quality
• Survival
• Food
• Age
• Sex
Host
• Genetics
• Behaviour
• Nutritional status
• Health status
What is Epidemiology?
Epidemiology is the science of
discovering causes of illness and
injury in populations.
Epidemiology studies are used to
control and prevent health
problems.
Number of Cases of a
Disease
Disease Patterns
Endemic
Epidemic
Time
 Endemic
 Transmission occur, but the number of cases remains constant
 Epidemic
 The number of cases increases
 Pandemic
 When epidemics occur at several continents – global epidemic
Outbreak Investigation
Basic steps in an outbreak investigation:
1) Gather information and confirm existence of outbreak
2) Confirm diagnosis
3) Establish a case definition – a standard set of criteria
for identifying who has the disease
4) Perform descriptive studies
5) Develop and test hypotheses
6) Implement control and prevention
7) Report findings
The Spread of Infectious Disease
an epidemiological simulation
Objective:
This activity will simulate the spread of an infectious disease.
Our simulation will show how an infectious disease can spread
from one infected person to other people, who in turn infect
others.
Hypotheses
1.
How many people will be infected after two rounds
of interactions? _______
2.
How many people will be infected after three
rounds of interactions?_______
Procedure
1.
Obtain a cup labeled A filled with a clear solution (body
fluid). Only one person in the class will have a cup that has
been “infected”. Do not drink from the cup.
2.
In this part of the activity, you will interact with two other
students. To interact with another student, pour all of your
solution into your partner’s cup, then have your partner pour
half of the mixed solution into your cup. Then move to another
part of the classroom and interact with a second student.
3.
Repeat step 2 with cup B, this time interacting with four
students.
4.
Your teacher or I will come around and put an “infection
indicator” in your cups. If you have exchanged solutions an
infected person, you are now infected and your solution will
turn pink.
Data Cup A
Your vial # _______
Name
1st
partner
2nd
partner
Your results______
Vial #
Dinner
Results
Data Cup B
Your vial # _______
Name
1st
partner
2nd
partner
3rd
partner
4th
partner
Same from
cup A
Same from
cup A
Your results______
Vial #
Dinner
Results
Analysis Questions
1. Who was patient zero?______________________
2. How many students in the class were infected after two rounds of interactions?_____
3. How many students in the class were infected after four rounds of interactions?_____
4. Was your hypothesis correct?_________________
5. How many people do you think would be infected if you had ten interactions? Explain.
6. What kind of mathematical model best explains your data (i.e. is the pattern random,
linear, etc.)?
7. List three infectious diseases you have heard of and how they are transmitted.
8. What are some ways you can prevent the spread of an infectious disease?