The Hijacker -- How a Virus Spreads
This lesson provides students with an understanding of how viruses attack the body, and
how the body's immune system defends the body from attack. Additionally, this lesson
simulates how any infectious disease travels through a population, and how scientists
trace the progress of epidemics such as AIDS. The use of video and the simulation of an
epidemic are intended to address the learning styles of both visual and tactile/kinesthetic-oriented students. Students will establish, through deductive reasoning, which student
was the initial carrier of the simulated disease, and how this disease spread throughout
the classroom population. This analysis will be aided by use of a graphic organizer. The
progression of this simulated epidemic will be linked to a real-life situation, the AIDS
Our Human Body from Science Source: #10 Viruses
Students will be able to:
- Describe how the body's immune system attacks invaders
- Explain the breakdown of the immune system in the disease AIDS
- Simulate the transmission of a viral infection
- Track the progress of a viral infection
- Graph the rate of infection in a population, using data collected in class
- Extrapolate from a graph to predict the future growth of an epidemic
- overhead projector
- transparency markers
- transparency, "Tracking an Epidemic"
(Before class begins, fill out this transparency with the names of each student)
- 1 disposable plastic transfer pipet
- distilled water
- 1% phenolpthalein solution (acid/base indicator)
- 1 M NaOH stock solution (dissolve 4 g of NaOH in 100 ml water)
- 0.1 M NaOH stock solution (dilute 1ml of 1 M NaOH in a total volume of 10 ml distilled
- test tube containing distilled water
- 1 or more test tube racks to hold class set of test tubes
- 1 plastic dishwashing pan, labeled "I was not infected"
- 1 plastic dishwashing pan, labeled "I was infected"
- 1 numbered test tube containing distilled water or 0.1 M NaOH (for a class of 25 students,
prepare 24 test tubes of distilled water, and 1 test tube of 0.1 M NaOH)
disposable 7-ml plastic transfer pipet (available from biological supply
- 1 pair of safety glasses/goggles
- pen or pencil
- 1 sheet graph paper
- 1 sheet notebook paper
- immune system
- acquired immune deficiency syndrome
Ask your students to turn to the person next to them and shake hands. Then, tell the
students, "Every time you shake a person's hand, you expose yourself to disease!" Elicit
discussion leading to the fact that our body's immune system is the body's defense
mechanism, by asking questions such as, "How does your body protect itself? If there are
germs or pathogens all around us, why aren't we sick all of the time?" Say, "It makes
sense to understand how our body fights disease, successfully and unsuccessfully, and
how diseases as common as a cold or as deadly as AIDS spread through populations. With
this information, we can prevent exposure to disease, remain healthy, and, possibly, find a
cure or vaccine. Then, hopefully, we can save lives."
Say, "Can anyone tell me what a hijacking is?" (A hijacker boards an airplane and takes it
over by force.) Ask your students, "How does the hijacker get past security? How does
he or she get the pilot to follow his or her orders? Are the people on board safe?"
Distribute a sheet of notebook paper to each student. Tell your students, "You are going to
watch a video that shows how one type of pathogen invades and hijacks the cells of your
body, and how your body's immune system launches a counterattack." To give students a
specific responsibility while viewing, say, "Look for the things that a virus does when it
hijacks your body, and write down those steps."
BEGIN tape where the video shows an image of frolicking seals; the words "Viral
infections" are written in the upper lefthand corner of the screen. Audio is, "Viruses are
specialized in attacking certain cells or bacteria." To allow students an opportunity to
record the sequence of events in a viral hijacking, PAUSE the tape at the end of the computer
animation sequence of viral invasion, replication, and cell death. Video is blue spiked viral
particles being released from yellow hepatic cells. Audio is, "...since the cell no longer
functions correctly." To check comprehension of the sequence of events that occurs during
a viral invasion, REWIND tape to the beginning of this animation sequence. Video is blue
spiked ball moving within a blood vessel. Audio is, "...they can undergo attack by many
different kinds of viruses. " Mute the sound. This will give students the opportunity to
focus on the animation sequence. Use the frame advance (or slow) option to move through
the tape slowly. Say, "Explain, step by step, the process occurring in the animation
(1.Virus travels through the body until it locates a target cell.
to the cell membrane.
3.Virus injects instructions into the cell.
4.These instructions alter
the cell's metabolism.
5.The cell begins to produce many copies of the virus.
viruses are released from the cell.
7.Viruses attack and often destroy other target cells.)
Pause the tape to allow students to finish recording their answers. Video is blue spiked
viral particles being released from yellow hepatic cells. Audio is, "...since the cell no
longer functions correctly."
Ask the students, "How will your body defend itself from this attack?" To give students a
specific responsibility while viewing, say, "Look for the molecule that the body produces,
and sketch it."
RESUME tape. Pause video with visual of orange cell producing Y-shaped
antibodies, so that students may sketch an antibody molecule.
FAST FORWARD tape. During this time, ask students to hypothesize what would happen if one
had no immune system. To give students a specific responsibility while viewing, say,
"Watch the video to find out what part of the immune system is missing when a person has
acquired immune deficiency syndrome."
BEGIN tape with visual of black monolith engraved
with the word AIDS; audio is, "AIDS, or acquired immune deficiency syndrome, is one
recent viral infection that is causing alarm all over the world." To give students the
opportunity to record their responses, PAUSE tape where video shows a virus multiplying
rapidly. Audio is, "The AIDS virus can remain dormant for several years before it
REWIND tape to the beginning of this second animation sequence. Video
is the image of 3 body cells and 1 virus particle. Audio is, "Once infection has taken
MUTE the sound. Use the frame advance option to move slowly through this
animation sequence. Ask the students to explain how this sequence is similar to and
different from the first animation sequence.
PAUSE tape at image of the
words, "SCI FAX More than 350,000 cases of AIDS were reported from 1981 to 1991.
How many survived?" Audio is the sound of a computer printer. Ask students to guess the
answer to that question.
STOP tape at the image of the answer, "none." Ask
the students, "Is this information correct? Are there any survivors of AIDS?"
discussion pertaining to the recent reports of several people who do not have symptoms of
AIDS who have been infected with the HIV virus for over 12 years.)
Additionally, in the
past year, one infant who was born HIV+ is now HIV-. Say, "Later, we will be looking at
how the AIDS epidemic has changed over time."
Say, "We've looked at how your body attacks most pathogens, and how it fails to attack
when infected with AIDS. Now, let's examine how any pathogen can spread from person
to person. At the beginning of class, I said that when you shake hands with someone, you
are exposed to many pathogens. Why do you think that is?" (When a person has a cold,
and sneezes or rubs his nose with his hand, any virus in that person's mucus ends up on
his hand. When you shake hands, the virus is transferred to your hand, and if you rub
your eyes, you may become infected.) Say, "Mucus, saliva, and blood are examples of
body fluids. Any virus or bacteria in your body can be spread if you share your body
fluids. Today we are going to demonstrate this. We are going to use liquids to represent
our body fluids. Each of you will get a test tube containing either pure water or a mystery
chemical." Remind students that they need to wear safety glasses, since they do not know
the identity of the liquid in their test tube. Distribute the handout "The Hijacker" and one
disposable transfer pipet to each student. Allow each student to select a numbered test tube.
Say, "Now that each of you has body fluids, I would like you to share with one other
person. Choose someone that you do not know too well. When I say "go," find your
partner. Ask your partner to tell you something new about herself. Write down this
information and your partner's name on your handout. Then trade 10 drops of body
fluids." Demonstrate how to transfer 10 drops of liquid. Say, "When I say 'stop,' return
to your seat." If there are an odd number of students, say "One of you will be my partner."
Give the signal to begin, and allow two to three minutes for this first trade. Give the signal
to stop and tell students the following: "Now you have shared body fluids with one person.
Before you find a second partner, be sure to do the following: Hold up your test tube and
transfer pipet, and squeeze the bulb on the pipet to return all liquid to the test tube." (It is
critical that students complete this task exactly as directed, to avoid confusing results.)
Give the signal to begin the second trade of body fluids, asking students to choose
someone from the other side of the room. (This is to ensure that small groups of students
do not interact with each other only.) Repeat this procedure for a third trade.
Say, "All of us should have traded our body fluids with 3 people. At the beginning of this
demo, one person was infected. Let's find out how many people are infected now." Ask
for three student volunteers. Say, "We are going to add an indicator dye to each sample of
body fluids. If you are infected, you will see a dramatic color change. Be sure to write
down the color of your solution." Ask the first volunteer to add two or three drops of
phenolpthalein to each test tube, using a clean transfer pipet. Do not touch the pipet to the
liquid in the test tube. Ask the second and third volunteers to collect the test tubes and
transfer pipets after a color change is noted. Uninfected samples should be collected in the
dishwashing pan labeled "I was not infected." (These pipets and test tubes are clean and
may be reused.) Infected samples should be collected in the dishwashing pan labeled "I
was infected." (These pipets should be discarded. Test tubes must be washed thoroughly
before reuse, to avoid false positive results.)
After all samples have been tested and collected, project the transparency "Tracking an
Epidemic." Ask students, "How many of you were infected? Would you like to know who
infected you?" Ask the students to raise their hands if they were infected. Note this on the
overhead by marking an asterisk next to the names of the infected.
Say, "How can we find out who infected whom?" Individuals may immediately give
reasons why he or she could not have been the original carrier. Direct these student
responses by saying, "In real life, scientists track epidemics in a very organized way. It
helps to chart the order that people interacted with each other, and to eliminate people, one
by one. Let's figure out the order first." Ask the infected students to list in order their
first, second, and third partner. Record this data on the transparency "Tracking an
After all infected students have provided data, say, "Now we need to begin eliminating
people. If a person was not the original carrier of the disease, he or she might have
interacted with people who did not become infected. Can anyone look at this data and find
a partner of an infected person who did NOT become infected?" If this person was not the
original carrier, he or she can be eliminated. Cross this person off the list. Ask the
students, "But who infected this person? It must be someone he or she interacted with."
Point out these partners on the transparency. Check one of these potential carriers next.
Did that person exchange fluids with someone who did not become infected? If so, he or
she is not the original carrier. Work backwards until you find two people who infected
each other. At this point say, "We have narrowed things down as far as we can. How can
we figure out who started the epidemic?" Explain that in real life, the time that a person
became ill is often used to figure this out, but sometimes it is impossible to determine who
started an epidemic. In this demonstration, students may be able to infer the original carrier
by observing the color of the solutions. The original carrier should have the most
concentrated base solution. The darkest pink sample contains the most sodium hydroxide,
and is the original carrier. If necessary, reveal the identity of the original carrier by giving
the number of the test tube which contained the sodium hydroxide solution.
Ask students to use the data on the transparency "Tracking an Epidemic" to create a table
that shows the number of people who were infected at the end of rounds one, two, and
three. Students should record this data in a table.
Distribute one sheet of graph paper to each student. Ask the students to create a line graph
to show this information in visual form. Allow time for the students to complete this
assigned task. Ask students to predict what would have happened if a fourth, fifth, or
sixth round of infection had occurred. Ask students to use their graphs to extrapolate these
further rounds of infection.
Ask students to predict how many rounds of infections would be needed to infect the entire
class. (At the end of the first cycle, a total of two students are infected. At the end of the
second cycle, four students are infected. At the end of the third cycle, up to eight are
infected. At the end of the fourth cycle, up to 16 are infected. At the end of the fifth cycle,
up to 32 are infected. This assumes that infected persons always exchange with
uninfected. It will take more cycles if students exchange body fluids randomly.)
Invite a physician from your city or county health department to speak about contagious
diseases, and how epidemics are tracked within your area.
Take a virtual field trip to one or more of the following sites on the World Wide Web:
This site contains an interview with Dr. Frederick Murphy, a researcher of the Ebola virus.
This Web site also has electron micrographs of this virus.
This site has beautiful electron micrographs of viruses, which may be viewed without
The World Wide Web server for the Institute for Molecular Virology at the University of
Wisconsin, Madison, is a colorful, user-friendly site that has a wealth of information on
viruses, including connections to other virology-related Web sites. Color images of many
viruses may be viewed at this site, or larger versions may be downloaded.
For the most current statistics on the spread of the AIDS epidemic, visit the World Health
Organization's Global Programme on AIDS.
Have interested students write a story about a viral hijacking from the point of view of the
virus or the point of view of the body. Reserve time for the students to present these
stories to the class.
Read the book THE HOT ZONE, by Richard Preston, which tells about recent efforts to identify new viruses
such as Ebola and track the spread of epidemics.
Use multimedia software such as Hyperstudio or Digital Chisel to create an interactive
tutorial on virus structure and function.
Research past epidemics, such as bubonic plague, polio, and influenza epidemics.
Compare the number of lives lost in these epidemics to the number of lives lost in different
Master Teachers: Veronica Zonick and Edna Soulas
Lesson Plan Database
Thirteen Ed Online