Epidemiology: Following an Infection

Many contagious diseases are caused by pathogens such as bacteria, viruses, or protozoa. The causative agent is spread by direct contact with someone who is infected or by indirect contact, as with water or objects contaminated by an infected person's body fluids or wastes (blood, saliva, feces, etc.). The dangerously rapid spread of Acquired Immune Deficiency Syndrome (AIDS) has caused a great deal of concern. Human Immunodeficiency Virus (HIV), the virus that causes AIDS, attacks and weakens the immune system by infecting T_H cells. HIV is transmitted from one person to another by the exchange of body fluids, including blood, semen, vaginal secretions, in utero, or breast feeding.

Epidemiologists study the causes and the spread of diseases through populations so that we can learn how to better control and prevent them. In this activity, we will model the spread of a disease and try to trace it back to Patient Zero.

Procedure

1. Take a cup containing a small amount of liquid representing a body fluid. One of the samples contains fluid “infected” with “HIV.”

2. A role card is attached to each cup which identifies a behavioral role telling you when and with whom you can exchange body fluids). You must keep this secret throughout the activity.

3. Choose a partner and ask their permission to exchange fluids. Do NOT tell the other person what your role is. If the person agrees, exchange fluids. You can exchange fluids only if the exchange is in keeping with your behavioral role, as stated on your role card. You cannot act out of character.

4. To simulate the exchange of body fluids, pour half of your fluid into the cup of another person. After your fluid is mixed with your partner, take back half of their fluid.

5. To keep track of who you exchanged body fluids with record each partner’s name in Table 1.

6. Before you find a new partner to exchange again, wait until you are told to do so.

7. After exchanging five times, get tested for HIV and record the result.

8. Repeat the activity ignoring your role, exchanging fluid with anyone.

Questions

Trial 1

1. Determine the identity of Patient Zero.

2. If you were infected, what was the behavioral role of the person who directly infected you?

3. What was the behavioral role of the person who started the infection?

Trial 2

4. Determine the identity of Patient Zero.

5. If you were infected, what was the behavioral role of the person who directly infected you?

6. What was the behavioral role of the person who started the infection?

7. Was there a difference between the number of people infected in trial 1 vs. trial 2?

8. Were you surprised at the number of people infected from the one original infected person?

9. Why is HIV so successful in infecting humans?

10. Was the epidemic a common-source epidemic or was it a propagated epidemic? Explain.

11. This is considered a propagated, behavioral risk related outbreak. What does that mean? Is HIV infection considered endemic, epidemic, or pandemic?

12. What is the adaptive value of having an immune system?

13. Describe what a vaccine is and explain how it might protect you from infection. Why is a vaccine useless after you’ve been infected?