Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Dilute the 0.1 M sodium hydroxide solution to 0.001 M:.
   1. Fill a 1-L Erlenmeyer flask about half full with distilled or deionized water.
   2. Measure 7 ml of the 0.1 M sodium hydroxide solution in a graduated cylinder. Add 7 mL of sodium hydroxide to the Erlenmeyer flask.
   3. Fill the Erlenmeyer flask to 700 mL with deionized water and mix well.
2. Number each test tube in sequential order.
3. Prepare the test tubes by filling all but one of the tubes required approximately one-half full with distilled or deionized water. This is about 20 mL of deionized water in each tube.
4. Fill the remaining tube (“the carrier”) to the same level as the other tubes with the 0.001 M sodium hydroxide solution. The carrier tube should appear exactly as the remaining tubes and be randomly placed among them in the test tube rack. Record the number of the “carrier” tube.
5. Set up a result grid on the white board or on an overhead. It will appear similar to the following chart. Write in the test tube numbers in sequential order in the first column.
   {11257_Preparation_Table_2}

Safety Precautions

Dilute sodium hydroxide solutions are skin and eye irritants. Thymol blue will stain skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Use forceps to retrieve any pipets that fall into the test tubes. Do not tip the test tube. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The resulting solutions may be disposed of down the drain with excess water following Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for five classes of 30 students. This laboratory activity can reasonably be completed in one 50-minute class period.
• Participants should be cautioned at the outset to exchange fluids carefully to avoid spillage. Spills should be absorbed on damp paper towels immediately. It is also possible for the pipet to fall into the test tube, in which case the student should not attempt to retrieve it with bare fingers or by tipping the tube. The instructor should retrieve pipets either with forceps or with gloved fingers. At no time should pipets be used by participants to “squirt” each other. The possibility of eye contact with dilute sodium hydroxide should be strictly avoided.
• It may be necessary to use a 0.01 M sodium hydroxide solution if more than 4 exchanges are used.
• The number of exchanges each participant conducts and the number of tubes initially “infected” will determine the ultimate rate of “infection.” For class sizes of 30 or less, one carrier should provide a dramatic result. The instructor should direct a minimum of two exchanges per participant for smaller classes but no more than four for up to 35 participants. It is important that participants circulate throughout the room or between groups following each exchange—this will ensure that the same few people do not simply keep re-infecting each other. When repeating the exercise, the instructor may wish to vary the number of exchanges, the number of initial carriers, or even to instruct one or more participants to “abstain” from exchanging.
• Thymol blue is a pH indicator. It is blue at pH levels of 9.8 or greater, yellow at pH levels between 8 and 2.8, and red at pH levels below 1.2. Check the pH of the deionized water before beginning. Deionized water is often slightly acidic due to carboxylic acid formed when the water is exposed to the carbon dioxide in air. The pH of the deionized water used to test this procedure was 5.5. Six exchanges from the original tube of 0.001 M sodium hydroxide still resulted in a positive-blue result.
• Tracking the original host is the most challenging aspect of the lab, especially when more than two exchanges occur. If students have a difficult time working from the result to the original host, have them work from the host forward to track who infected whom.

Teacher Tips

• Although the Background section focuses on EBV, the same activity can be used to focus on sexually transmitted pathogens, such as HIV.
• Extend the learning by assigning pathogens to be researched to students. Have them create a mini-lesson or poster with information (e.g., type of pathogen, method of infection, vaccines or treatments).

Answers to Prelab Questions

1. Read the Safety Precautions section. Why is it important to protect skin and eyes from the liquid used in this lab activity?

   The solutions used are skin and eye irritants and will stain skin and clothing.

2. Of the diseases listed in the Introduction and Background sections, only one has a vaccine associated with it. Using other reference sources, such as your textbook or an Internet site like www.nih.gov, research which disease has a vaccine and how vaccines work to protect against the disease.

   Mumps is the only disease listed that currently has a vaccine. The mumps vaccine is a live, attenuated vaccine. The vaccine is injected into the body where the person’s immune system is able to react to the weakened virus and to create immunity to the virus should it ever enter the vaccinated person.

Sample Data

Answers to Questions

1. Determine which test tube initially contained the simulated saliva and record your choice below.

   Student answers will vary. In the example above it is test tube 1.

2. Describe how you determined your choice.

   Student answers will vary but should include a discussion of the test result color and tracking the color. The best way to determine the initial test tube if you need to help is to cross out the numbers of those tubes that tested yellow. Then look for a pattern. In the example above, tube 20 tested blue but it exchanged with tubes 6 and 18 which remained yellow. Consequently it was the last tube, number 1, that caused 20 to be blue. Work backwards if possible. This demonstrates how difficult tracking the source can be. If need be, give the students the number of the initial tube, in our example tube 1, and let them work it forward.

3. As a class, reach a consensus on which test tube initially contained the simulated saliva. Did the majority of the class agree with your initial choice?

   Student answers will vary.

4. Epidemiologists are scientists who try to determine the cause of an outbreak of disease. Besides laboratory test results, epidemiologists often interview the patient and family members. Hypothesize why interviews are important in tracking the initial host for a disease outbreak.

   The actual pathogen will help narrow how it was transmitted but does not allow the epidemiologist to determine exactly who (or what) is responsible for the outbreak of disease. Patient interviews regarding where they’ve been, what they’ve eaten, and so on will help narrow the potential host further. Once the choices have been narrowed down to a few possibilities, the epidemiologist can request tests to confirm the host.

References

Centers for Disease Control and Prevention. About Epstein-Barr Virus (EBV). http://www.cdc.gov/epstein-barr/about-ebv.html. (accessed April 2014)

Understanding Vaccines. NIH Publication No. 08-4219, National Institute of Allergy and Infectious Diseases (NIAID). Updated January 2008. http://www.niaid.nih.gov/topics/vaccines/documents/undvacc.pdf (accessed April 2014)

Introduction

The exchange of body fluids, such as saliva, is a very common method of infection. Some diseases that may be acquired by the exchanging of saliva include mononucleosis, strep throat, cold sores and mumps. This activity mimics the exchange of saliva and therefore the potential to transfer a pathogen by kissing.

Concepts

• Infectious disease
• Pathogen
• Virus

Background

Infectious and parasitic diseases are spread from person to person mainly through air, water, and physical contact by way of small organisms called pathogens. Most pathogens are difficult to avoid as they cannot be seen and symptoms occur after the infected individual is contagious. Examples of pathogens are viruses, bacteria, fungi and infectious parasites such as Plasmodia, amoebae and nematodes.

Saliva contains immune cells but certain pathogens take advantage of these cells and replicate within oral tissues where they are able to spread to the next host. The Epstein-Barr virus (EBV) that causes mononucleosis (mono) is one of these. In developed countries, mononucleosis is also known as the kissing disease because of its tendency to infect young adults. In undeveloped countries, EBV infection occurs in early childhood and the virus doesn’t develop into mononucleosis. The Centers for Disease Control estimates that 95% of all adults in the United States have been infected by EBV with 25% of those infected showing the symptoms of mono. Anyone infected with EBV will remain infected because EBV does not just remain in the active infection/growth phase. The virus enters into the immune system’s B-cells where it becomes latent. Although unlikely, it is possible for the virus to immerge from the latent phase and become viral once again.

Kissing is just one way saliva is exchanged. Sharing utensils, bottles and cups can lead to infection as well. With the reduced amount of saliva though comes a reduced likelihood of infection, however, it does only take one virus to cause infection.

Experiment Overview

In this activity, the exchange of simulated saliva mimics the sharing of a beverage contaminated with an infectious virus. By documenting the exchange partners, it is possible to trace the infection to the original host.

Materials

Prelab Questions

1. Read the Safety Precautions section. Why is it important to protect skin and eyes from the liquid used in this lab activity?
2. Of the diseases listed in the Introduction and Background sections, only one has a vaccine associated with it. Using other reference sources, such as your textbook or an Internet site like www.nih.gov, research which disease has a vaccine and how vaccines work to protect against the disease.

Safety Precautions

The solutions used in this activity are skin and eye irritants and will stain skin and clothes. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Write your test tube number on the Infection! Worksheet.
2. Find another student with whom to exchange the solution in the test tube.
3. Use the disposable pipet to remove 3 mL of the solution from your test tube. Being careful not to contaminate the test tubes, gently squeeze the solution into the other person’s test tube. The other person should put a similar amount of solution into your test tube, having removed the solution before you added yours. Note: See the teacher if a pipet falls into the test tube.
4. Write down the test tube number of the other student on the Infection! Worksheet.
5. Repeat steps 2–4 with additional partners, making sure they have not exchanged solutions with anyone who has already exchanged with you.
6. After completing three exchanges, place the pipet onto the paper towel and proceed to the testing solution area.
7. Place 3–4 drops of thymol blue indicator into the test tube. Thymol blue will appear blue or green in test tubes that contain the simulated virus. A yellow color indicates no exposure.
8. Write your results in the data table on the Infection! Worksheet. Fill in your exchange information in your row on the board. For example, if you had test tube 1 and you exchanged with test tubes 2, then 10, then 20 on the board table, you will fill in test tube row one. Write the number 2 in the 2nd column, 10 in the 3rd column, and 20 in the 4th exchange column.
9. Next, fill in the color of your test tube’s solution. Using test tube 5 as our example again, let’s assume it became blue in step 7. Find test tube 5 in each column on the board and write blue next to the number.

   Sample of Data Table

   {11257_Data_Table_1}
10. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

11257_Student1.pdf