Infectious DiseasesInfectious Diseases

Presented by: M. AlvarezAdapted from:M. Arias, C. Goedhart, and M.Burke

What is an Infection?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 diseaseBACTERIA

Tuberculosis, pneumonia, salmonella, anthrax FUNGUS

Athlete’s foot, ring wormPROTISTS

Malaria, toxoplasmosis, Algae

A harmful invasion and spread of foreign species, or pathogen, in a host. VIRUS

Small pox, measles, influenza, Ebola PRIONS

Cow’s diseaseBACTERIA

Tuberculosis, pneumonia, salmonella, anthrax FUNGUS

Athlete’s foot, ring wormPROTISTS

Malaria, toxoplasmosis, Algae

Infectious Agents

Worldwide mortality due to infectious diseases

Worldwide mortality due to infectious diseases

Estimated number of people in the world living with

HIV/AIDS in 2008

Estimated number of people in the world living with

HIV/AIDS in 2008

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

P

S

S

T

Susceptible

Immune

Sub-clinical

Clinical

ST

Spread of Disease & Transmission

Infection in one person can be transmitted to others

Transmission of Pathogens

•Direct contact

•Indirect contacts•Air•Objects

•Vectors

Routes of transmissionRoutes of transmission

Direct Skin-skin

Herpes type 1 Mucous-mucous

STI Across placenta

toxoplasmosis Through breast milk

HIV Sneeze-cough

Influenza

Indirect Food-borne

Salmonella Water-borne

Hepatitis A Air-borne

Chickenpox

Vector A carrier of an infectious agent

Ex. Malaria Parasite carried by Mosquito

Agent

Host

Environment

• Age

• Sex

• Genetics

• Behaviour

• Nutritional status

• Health status

• Infectivity

• Pathogenicity

• Virulence

• Antigenic stability

• Survival

• Weather

• Housing

• Geography

• Occupational setting

• Air quality

• Food

Factors Influencing Disease Transmission

What is Epidemiology?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.

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

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

Endemic Epidemic

Nu

mb

er o

f C

ases

of

a D

isea

se

Time

Disease Patterns

Outbreak InvestigationOutbreak Investigation

Basic steps in an outbreak investigation:Basic steps in an outbreak investigation:

1)1) Gather information and confirm Gather information and confirm existence of outbreakexistence of outbreak

2)2) Confirm diagnosisConfirm diagnosis

3) Establish a case definition – a 3) Establish a case definition – a standard set of criteria for standard set of criteria for identifying who has the diseaseidentifying who has the disease

4) Perform descriptive studies4) Perform descriptive studies

5) Develop and test hypotheses5) Develop and test hypotheses

6) Implement control and prevention6) Implement control and prevention

7) Report findings7) Report findings

The Spread of Infectious Diseasean epidemiological simulation

The Spread of Infectious Diseasean 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?_______

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?_______

ProcedureProcedure1. 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. 

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 AData Cup AData Cup AData Cup AYour vial # _______ Your Your vial # _______ Your results______results______

Your vial # _______ Your Your vial # _______ Your results______results______

NameName Vial #Vial # DinnerDinner ResultResultss

11stst partnepartnerr

22ndnd partnepartnerr

Data Cup BData Cup BData Cup BData Cup BYour vial # _______ Your Your vial # _______ Your results______results______

Your vial # _______ Your Your vial # _______ Your results______results______

NameName Vial #Vial # DinnerDinner ResultResultss

11stst partnepartnerr

22ndnd partnepartnerr

Same from cup A

33rdrd partnepartnerr

44thth partnepartnerr

Same from cup A

Analysis QuestionsAnalysis 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?