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Title: Simulating the Spread of an Infectious Diseases
From the bubonic plague, to AIDS, to the Guinea worm parasite, scientists and public health officials have struggled to understand and contain the spread of infectious diseases. Using simple reagents, students can simulate the spread of a simple imaginary disease in order to explore some factors that affect the rate of infection, the challenges of epidemiology, and measures which can help prevent the spread of disease.
Principle(s) Investigated:
- interactions among organisms
- rate of transmission of infectious diseases
- preventing the transmission of diseases
- pathogens
MS-LS2-2.
Construct an explanation that predicts patterns of interactions among organisms across multiple ecosystems
MS-ETS1-1
Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.
Science and Engineering Practices
• Asking questions (for science) and defining problems (for engineering)
• Analyzing and interpreting data
• Constructing explanations (for science) and designing solutions (for engineering)
• Engaging in argument from evidence
Crosscutting Concepts
• Patterns
• Cause and effect: Mechanism and explanation
Materials:
- Test tube* and dropper for each participant
- Distilled water**
- 0.1 molar NaOH
- Phenolphthalein solution
- tape and marker to number test tubes
*You can also use disposable cups if you do not have test tubes, or you do not trust younger students with glass.
**Distilled water may not be necessary. If you test the tap water with the indicator and there is no color change, you can use it.
Procedure:
1. You will be modeling the transmission of a disease by exchanging some of your test tube's contents with other students. One of the test tubes is "infected" with an imaginary infectious disease. You do not know which one it is.
2. Test tubes have been prepared prior to activity by the teacher. Retrieve one test tube and dropper from the teacher.
3. Leave your seats and spread out though out the classroom. Once instructed by the teacher, move around the room. Be careful to not bump into other students or desks.
4. When the teacher says "Stop!", use your dropper to trade fluid with the person nearest you. Be careful not to touch other students' fluid with your dropper. The teacher will have you stop and trade fluid at least three times. Record the number of the test tube you exchanged fluids with HERE.
5. Now it's time to test for the imaginary infection. The teacher will come around and put a drop of phenolphthalein in each test tube. If your fluid turns pink, it is "infected".
6. As a group, use the data to try to deduce which individual was the original carrier of the "disease".
CAUTION: Sodium hydroxide (NaOH) and phenolphthalein can irritate the eyes and skin. Alert students to avoid spilling and warn them to NEVER drink what is in the test tube.
Student prior knowledge:
- Prior to this activity students should know the following vocabulary:
Pathogens: An agent that causes infection or disease, especially a microorganism, such as a bacterium or protozoan, or a virus.
Outbreak: a sudden rise in the incidence of a disease
- Students should also know the different modes of transmission of diseases.
- Students should know the difference between bacteria and a virus.
Explanation:
How to Prepare Lab: Prepare the test tubes prior to the activity. Fill one tube halfway with 0.1 molar NaOH and one with the phenolphthalein solution; fill the rest of the tubes halfway with distilled water. If you have a large group (35 or more) you may want to begin with two test tubes containing NaOH. Explain to students that they are going to model the transmission of a disease by exchanging some of their test tube’s contents with that of other participants. Mention that one of the test tubes is "infected" with an imaginary infectious disease. Distribute prepared test tubes and droppers to the class. Make a mental note of who receives the test tube containing NaOH. Keep the test tube with the phenolphthalein.Have participants walk around the room with their test tubes. When you say "Stop!", each participant should use a dropper to trade a drop of fluid with the person nearest them. Repeat until at least three trades have occurred. Put a drop of phenolphthalein in each test tube. If the fluid turns pink, the cup is "infected" with NaOH. The final number of "infected" test tubes will vary depending on (1) the number of trades and (2) how many trades occur between two already infected tubes.
Why does the "infected" solution turn pink?
Reaction between Phenolphthalein(H2ln) and Sodium Hydroxide(NaOH):
H2ln + 2 NaOH ---> ln2- + 2 Na+ + 2 H2O
In the pH range of 8.2-10 both acidic protons are rapidly removed from the colorless H2ln by NaOH,(OH-) resulting in the product of ln2- ions and a pink color.
How to determine "patient zero": The sample chart shows one example of how to trace the infection (bolded names are infected). Participants who "test positive" and find that everyone with whom they traded also tested positive may be original carriers of the disease (Cal, Dee, Gib, and Hal in this example). It is likely that there will be several candidates for "patient zero." Cross-checking the history of each contact can narrow the field, but probably not to less than two candidates. (For example, here, Cal and Dee can be eliminated as "patient zero" because their first contacts, Bob and Ed, did not infect their own second contacts, Fran and Ilsa; either Gib or Hal, however, could be "patient zero.") If participants are unable to reach a clear conclusion, the exercise will raise useful questions about the challenges facing real epidemiologists as they try to trace the sources of an infection.
Sample Chart Tracing Infection
Questions & Answers:
1. Why might it be important to locate the source of infection?
Answer: We refer to the source of infection as the origin from which a host acquires the infection, either endogenous (i.e. originating from a person's own commensal microbial flora) or exogenous (i.e. an individual, animal or object that in the external environment of the host). Usually the source can be identified as an individual, animal or object in a specific place, and at a specific time. Identifying the source will hopefully lead to containment and possible treatment.
2. Note that the simulated disease has a 100% rate of infection that appears immediately under testing. Some infections, such as AIDS and chicken pox, can remain dormant in the body for a long time. Others, such as Ebola, kill the host rapidly. How might each of these factors affect the spread of disease?
Answer: If a disease kills its host rapidly, then there is less of a chance for it to be spread to others. This is because there is less time for the infected host to interact with others and spread the disease. Diseases that remain dormant in their hosts increase the chance that they will spread. Since the host does not know that they are infected, they are likely to interact with people as usual and therefore spread the disease.
3. What are some ways of preventing the transmission of diseases?
Answer: Barriers can be used as a form of preventing transmission. Such barriers include wearing masks to prevent the escape of mucus and saliva, as well as condoms in preventing the spread of STDs, and mosquito nets to prevent the spread of West Nile virus. There are also immunizations and therapeutic drugs. Furthermore, some people are born with a natural immunity which originates from somewhere in their genetic make up.
Applications to Everyday Life:
1. This lab can also be used in health classes, as it is a great way to demonstrate the spread of sexually transmitted diseases.
2. The topic of disease transmission is very relevant right now with the outbreak of Ebola. This lab can help students have a better understanding of how Ebola is spread. An educated population can help prevent panic as well as the further spread of the Ebola virus.
3. This type of demonstration may also be slightly adapted and used to demonstrate the spread of different populations of people throughout history and how their genes were spread across the world.
Photographs:
Videos:
For a computer based, interactive activity about the transmission of diseases go to Explorelearning.com and click on “Browse Gizmos.” Select “Biology” and then “Human biology, anatomy, and health.” Find “Disease Spread” and click on “Launch Gizmo.”
Source: This activity is based in part on an activity presented at: www.pbs.org/wgbh/aso/resources/guide/medact4index.html.
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