of extreme poverty, infectious diseases remain the leading cause of death.
In the United States, prevention and control of infectious diseases have
been so successful in the past half century that many people view
infectious diseases as either a thing of the past or minor illnesses easily
treated and cured, except among the very young, very old, or seriously ill.
In recent years, however, Americans have been shocked by the emergence
of a variety of “new” infectious diseases. For example, Escherichia coli
strain O157:H7 caused vomiting and severe diarrhea among children
swimming in public pools in Atlanta, Georgia, in 1998, and among 58
people across nine states in 2011 who ate romaine lettuce tainted with
the bacteria. A previously unrecognized virus (a hantavirus) caused a
frequently fatal respiratory illness among apparently healthy young people
in the Southwest. New diseases have emerged in developing countries as
well. Ebola hemorrhagic fever, which was first described in 1976 in Zaire
(now the Democratic Republic of the Congo), has particularly horrifying
symptoms and a fatality rate of 50 to 90 percent. West Nile virus, first
isolated in Uganda, is now found in other African countries, West Asia,
Europe, and the Middle East. And AIDS, which emerged simultaneously
in the United States and Africa in the early 1980s, has become a
global pandemic.
Likewise, many diseases thought to be adequately controlled appear to
be making a comeback. In developed countries, public health measures
such as sanitation, sewage treatment, vaccination programs, and access to
good medical care—including a wide range of antibiotics—have virtually
eliminated “traditional” diseases such as diphtheria, whooping cough,
and tuberculosis. However, many of these diseases are becoming a public
health problem once again, as immunization programs and other public
health standards are enforced less vigorously and, especially, as antibiotic-
resistant pathogens evolve. In fact, medical workers have identified strains
of pneumonia-causing Staphylococcus aureus that are resistant to all of
the currently available drug treatments, and physicians and public health
workers are concerned that we are about to re-enter the preantibiotic era
for treating such diseases, especially with inexpensive drugs. Among
the diseases “re-emerging” as a consequence of microbial resistance are
tuberculosis and gonorrhea, a leading cause of death from infectious
diseases worldwide and a major cause of infertility, respectively.
This lesson engages students in the seriousness of infectious diseases by
helping them become aware of the widespread impact of such diseases.
Students discover that some diseases are relatively new to humankind
(emerging diseases), while others that had been nearly eliminated
in developed countries are now beginning to increase in incidence
(re-emerging diseases). They also learn that many diseases have been
a perennial problem in human populations, never significantly
declining (endemic diseases).
50
Photocopies and Transparencies
Equipment and Materials
In Advance
• 1 transparency of Master 1.1
• 1 overhead projector
for the class
• red transparency pen
• 1 copy of Master 1.2
• (Optional) computers with
for the class
access to the Internet
• 1 transparency of Master 1.3
for the class
Preparation
Make the disease cards: copy Master 1.2, and cut the copy apart to form
individual cards. Glue each card to a 5 × 7 index card.
Note to teachers: Lesson 3 includes a bacterial growth experiment. If you
are teaching the lessons on consecutive days, students will need to complete
Steps 5 to 8 on Master 3.1b, Bacterial Growth Experiment, during this class
session. See Master 3.1b for details. (Students should have completed
Steps 1 to 4 in 2 to 3 days before this class; see suggested timeline, page 16.)
1. Introduce the module and this lesson by asking students, “What
Procedure
disease do you think is the greatest threat to students in this class?
What disease do you think is the greatest threat to the world’s
population?” Solicit several responses and entertain a brief
discussion about the diseases students perceive as threats and why.
List students’ responses on the board or a transparency.
If you can project the
Heart disease was the top killer globally in 2008. AIDS and cancer
video “Infectious Disease
are likely to be two of the top threats students perceive. According
Then and Now” from the
to the World Health Organization (WHO), in 2008 HIV/AIDS was the
Web site to the whole
sixth-highest killer worldwide, while cancer of the trachea, bronchus,
class, you can substitute
or lung was the seventh-highest killer. Also in the top 10 killers globally this video for the quiz.
were stroke and other cerebrovascular disease (2nd), pneumonia (3rd),
chronic obstructive pulmonary disease (4th), diarrheal diseases such
as cholera (5th), tuberculosis (8th), diabetes mellitus (9th). (8th),
diabetes mellitus (9th).
supplements/diseases, and click on “Web Portion of
2. Tell students that, as a class, they will take a quiz on some past and
Student Activities” and
current causes of death and illness. Explain that you do not expect
then on “Lesson 1—
them to know the answers to these questions, but ask them to make
well-reasoned guesses based on what they do know. Then, display a
Infectious Disease Then
transparency of Master 1.1, Causes of Death Quiz, solicit students’
and Now.” The video
answers to each item, and provide the correct answers.
covers roughly the same
content and may take less
time than the quiz. Both
the quiz and the video
serve an Engage role for
this lesson and the module.
51
Student Lesson 1
Emerging and Re-emerging Infectious Diseases
Question 1. Which of the following diseases has been recognized
since antiquity?
(c) Guinea worm disease, or dracunculiasis, is mentioned in biblical
texts. Although it is unfamiliar to Americans, it is not uncommon on
the Arabian peninsula and sub-Saharan Africa. The disease is caused
by a parasitic roundworm that is ingested in a larval form. The larvae
migrate through the tissues where they mate and grow. A year after
the larvae are ingested, a mature female migrates to subcutaneous
regions, typically in the legs and feet. The worm may reach a yard in
length. Its migrations cause great pain and inflammation, a burning
itch, and subcutaneous ulcers. One form of treatment is to wet the
skin to stimulate the worm to stick its head out and catch the head
in a split stick. The worm is then slowly extracted, over the course
of several weeks, by rolling it around the stick (if it is pulled too
quickly, the worm will break in two, causing greater problems). This
treatment may be the ori gin of the caduceus symbol that represents
the medical profession. Students will learn as they complete this
lesson that Legionnaire’s disease and Ebola fever were first recognized
as distinct diseases in 1976, and AIDS first came to worldwide
attention in the early 1980s.
Question 2. In the 1700s and 1800s, a terrible, wasting disease killed
thousands of European and American city dwellers. What disease
was this?
(d) Tuberculosis (TB) killed 1 of every 4 Americans in the 1800s.
The disease is still a leading killer globally, although it had decreased
dramatically in the United States until the AIDS epidemic. The
immune system of most people who contract the bacterium that
causes tuberculosis successfully prevents its growth, and active
disease never develops. Any condition that compromises the immune
system, such as HIV infection, will allow the bacteria to grow,
resulting in active tuberculosis.
Question 3. What infectious disease causing severe fever and chills
plagued settlers in the Southern and Midwestern United States during
the 1800s and early 1900s?
(c) Malaria is thought to have been introduced to the United States
from Europe and Africa in the 16th and 17th centuries. The incidence
of malaria in this country probably peaked around 1875. In a review
of U.S. malaria outbreaks, J. Zucker estimated that more than 600,000
cases occurred in 1914. Improved socioeconomic conditions, mosquito-
control measures, and availability of effective drugs later led to the
virtual elimination of this disease in the United States, although
localized outbreaks are still occasionally reported.
52
Question 4. Most deaths among U.S. servicemen in 1918 were due to
what cause?
(b) Flu caused most of these deaths. The global influenza epidemic of
1918 is estimated to have killed 30 million people. The movement of
troops during World War I, accompanied by crowding, poor nutrition,
and generally poor living conditions, probably contributed to the rapid
spread of the flu around the world. The 1918 flu was particularly
virulent and, unlike typical flu epidemics, caused death more frequently
among young adults than among children and elderly people.
Question 5. In 1994, a terrible disease nearly killed an 18-year-old high
school student in California. Which of the following diseases was it?
(d) Tuberculosis (TB). The student contracted TB from a classmate at
her high school, who had an active, misdiagnosed case of the disease.
An additional 11 students at her school developed active cases of TB,
and several hundred more had positive skin tests, indicating that they
had been exposed. The student tells her story in Lesson 3, Superbugs:
An Evolving Concern.
Question 6. According to the World Health Organization, which of the
following diseases caused more deaths in 1998 and 2008 than the others?
(d) Pneumonia was the third-highest killer in 1998, behind heart
disease and cerebrovascular disease. By 2008, the leading cause
of death was heart disease, followed by stroke and other
cerebrovascular disease.
3. Explain that the quiz emphasized the impact of infectious diseases
on people’s health and well-being. Point out that even though medical
advances in the last century have resulted in far fewer deaths from
infectious diseases than at any other time in history, those diseases
are still the leading cause of death worldwide and the third leading
cause of death in the United States. Explain that in this lesson,
students will learn about some infectious diseases that cause
problems in the world today.
You may need to distinguish infectious diseases from noninfectious
diseases. Ask students to review the Causes of Death Quiz and identify
some of the infectious and noninfectious diseases listed there. If
necessary, point out that noninfectious diseases such as most cancers,
heart disease, and cystic fibrosis cannot be “caught,” and that infectious
diseases such as AIDS and tuberculosis are caused by living (or
quasi-living, in the case of viruses and prions) agents that can be
transmitted from one individual to another.
Identifying a disease as “infectious” or “noninfectious” has recently
become more complex than it used to be. Researchers have discovered
that infectious agents may play a role in some diseases that were
53
Student Lesson 1
Emerging and Re-emerging Infectious Diseases
previously considered noninfectious, chronic conditions. For example,
there is evidence that most gastric ulcers are caused by Helicobacter
pylori bacteria, and that there’s a link between toxoplasmosis
and schizophrenia. Similarly, infection by Chlamydia pneumoniae
and periodontal disease may contribute to the development of
cardiovascular disease, leading some people to question whether
heart disease might be infectious.
4. Organize students in groups of three and distribute five Disease Cards
made from Master 1.2 to each group.
Distribute the cards in such a way that each disease is reviewed by
Circulate among the groups
at least one group.
while they catego rize their
diseases in Steps 5, 8,
5. Explain that scientists find it useful to group diseases in different
ways, depending on the problems they want to address. As an
and 10 for an informal
example, display the first classification criterion on Master 1.3a,
assessment of students’ skills
Disease Classifications, and direct the groups to review their disease
in orga nizing information.
cards and sort them into piles that represent different categories of
infectious agents.
An important science process skill is identifying commonalities and
differences and devising classification systems. In this step, students
have the opportunity to practice this skill, and in Steps 7, 9, and 10,
they consider the usefulness of classifying diseases in various ways.
The discussion in Steps 7
6. Solicit headings for the categories identified from several groups
and 9 are opportunities to
and write them on the appropriate place on Master 1.3a. Then, ask
point out the contribu tion
the other groups to name one or more diseases they classified in the
of basic research to the
categories and write these into the appropriate rows. Ask students
development of effective
to describe the symptoms of each disease as they do so.
treatments and preventive
measures for many diseases.
7. Ask students to suggest reasons why scientists might find it useful
For example, research on the
to classify diseases based on the type of infectious agent.
life cycle of Schistosoma
identified snails as an
If students need help with this, ask them to review the treatment for
intermediate host, revealing
each of the diseases within a category and each disease’s symptoms.
an important point for
Students should notice that diseases caused by the same type of
infectious agent tend to have similar types of treatment strategies,
preventive measures.
and that similar symptoms occur in diseases caused by different
Scientists also recently
types of agents. It is useful to classify diseases by the type of
discovered a drug that kills
infectious agent because that is a better indicator of the type
adult schistosomes, reducing
of treatment that may be effective than is a list of symptoms.
the possibility of severe liver
disease and inter rupting the
8. Reveal the next classification criterion, on Master 1.3b, and ask
organism’s reproductive cycle.
students to re-sort their disease cards based on this criterion
Continuing research likely
(the mechanism of transmission for each disease).
will lead to effec tive treatment
and pre ventive measures in the
future for diseases like AIDS
that are currently incurable.
54
9. Repeat Steps 6 and 7 for this criterion.
It is useful to classify diseases by the way they are transmitted
because a disease’s mode of transmission may suggest an effective
preventive measure. For example, the spread of diseases such as AIDS
and Ebola hemorrhagic fever that are transmitted by intimate contact
can be stopped or reduced through education and elimination of
some behaviors (such as burial practices in which family members
disembowel the deceased in nonsterile conditions) and institution of
other behaviors (such as proper disease-control measures in hospitals).
The spread of vector-borne diseases such as malaria can be prevented
by measures that treat people, reduce the size of the vector population,
or limit contact between humans and the vector.
10. Reveal the last classification criterion, history of the occurrence of
the disease, on Master 1.3c, and ask students to re-sort their cards.
Then, repeat Steps 6 and 7.
Students likely will identify two categories: “new” (for example, AIDS,
Ebola, and Legionnaire’s disease) and “old” (for example, strep throat,
guinea worm disease, pneumonia, polio, and tuberculosis).
If this is the case, add these headings to the first two rows on Master
1.3c and list the diseases named by students. Then challenge them
to re-examine the “old” diseases they listed and to subdivide that
category. Help them by asking a question such as, “Is there any
difference in the history of the ‘old’ disease tuberculosis and the
‘old’ disease pneumonia?” When students make the appropriate
distinction, add the new headings for the second and third rows
on Master 1.3c and relist the diseases accordingly.
Students should note that whereas all the old diseases are described as
“present from antiquity,” the incidence of some of them has increased
recently (in particular, the incidence of some has increased recently
after declining in the past). The categories from the subdivided “old”
category could be renamed “Old and Increasing,” “Old and Remaining
Constant,” and “Old and Changing/Evolving.”
11. Supply the headings “Emerging” for the apparently new diseases,
“Re-emerging” for diseases that have recently increased in incidence
after a decline, and “Endemic” for diseases that have remained
relatively constant in incidence. Write these labels at the heads
of the appropriate rows.
This step focuses stu dents’
attention on the major
The disease cards provide examples of all three types of diseases, as
concept of this activity
shown in Figure 9.
and the module: Infectious
diseases are an increasing
Both polio and guinea worm disease have declined dramatically and, we health concern in part hope, are on their way to global eradication. Cholera and influenza are
due to emerging and
more complicated examples that are less easily classified. On the basis
re-emerging dis eases.
of the information on their cards, students will likely classify cholera as
55
Student Lesson 1
Emerging and Re-emerging Infectious Diseases
a re-emerging disease and influenza as an endemic disease. Depending
on the sophistication of your students and the time available, you may
simply accept their initial categorization or you may choose to share
the additional information below and ask them where they would
categorize these two diseases. In either case, note that the categorization
of infectious diseases into these three areas is somewhat subjective,
and different researchers may categorize them differently based on the
weight they give to various characteristics.
Cholera may be classified as either re-emerging, because of increasing
incidence due to the spread of the disease to Africa, or emerging,
because of the appearance of the new serotype Vibrio cholerae O139.
This new serotype evades the immunity developed to previous cholera
strains, so it can infect a population that had developed immunity.
Influenza is probably most accurately classified as an emerging
disease because, although the flu occurs every year, each strain
of the influenza virus is genetically distinct. In this sense, it is a
constantly emerging pathogen.
You may also want to elaborate on the definition of emerging diseases
by noting that this category includes 1) diseases that are truly “new”
among humans (few, if any, examples fall into this subcategory); 2)
diseases that probably affected a few individuals even hundreds and
thousands of years ago but have just recently affected enough of the
population that they are noticed (AIDS and Ebola hemorrhagic fever
are examples for this subcategory); and 3) diseases that affected
people hundreds and thousands of years ago but have just recently
been recognized as due to an infectious pathogen (gastric ulcers
caused by Helicobacter pylori is an example that falls into this
subcategory). Many researchers include re-emerging diseases as
a subcategory of emerging diseases.
Figure 9. History of occurrence.
Category
Diseases
Emerging Diseases
AIDS, cholera, CJD, Ebola hemorrhagic
fever, influenza, Legionnaire’s disease,
Lyme disease
Re-emerging Diseases
tuberculosis, malaria, schistosomiasis
Endemic Diseases
pneumonia, polio, guinea worm disease,
plague, strep throat
56
12. Conclude the lesson by telling students that public health workers
are becoming increasingly concerned about the emergence of “new”
diseases and the re-emergence of some “old” diseases. These biologists