Emerging & Re-emerging Infectiious Diseases
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PDF Files for PrintingActivity 2 - Disease Detectives

At a Glance

Focus: Students assume the roles of public health experts to investigate the cause of a mystery disease.

Major Concepts: A major cause of the emergence of new diseases is environmental change (for example, human encroachment into wilderness areas and increased human traffic through previously isolated areas).

Objectives: After completing this activity, students will

Prerequisite Knowledge: Students should know that infectious diseases are diseases that result from the presence of an external agent or its products. Students should also know that antibodies are produced by the body in response to invasion by a foreign organism or molecule, and that the presence of particular antibodies indicates a previous encounter with the foreign agent that triggered their production. They should also understand that purified antibodies to a particular organism or molecule can be used to detect that organism or molecule in tissue samples from victims of an infectious disease.

Basic Science-Public Health Connection: This activity demonstrates how scientists use ecological, biochemical, and medical research to investigate infectious disease outbreaks. The activity also illustrates how the results of such research can help stop epidemics and lead to public health recommendations and the development of drugs and vaccines to limit future epidemics of the disease.

Introduction

When local health care workers recognize a cluster of strange disease cases with similar characteristics, they bring it to the attention of national public health officers. Epidemiologists collect a variety of evidence including demographic evidence (such as geographic location, age and other defining characteristics of victims, and mortality rate), laboratory evidence from victims' tissues, and evidence about environmental factors that might be involved. Their goal is to protect public health by identifying the disease as rapidly as possible and recommending appropriate actions to prevent it from becoming an epidemic.

A recent example of the effectiveness of this strategy was the identification of hantavirus pulmonary syndrome (HPS) as an emerging disease. Cases of this apparently new disease were first recognized in May 1993. Within four months, the infectious agent had been identified as a "new" variety of hantavirus, the reservoir of the virus had been determined to be deer mice, and the route of transmission (inhalation of viral particles from the rodents' feces and urine) had been deciphered. Strategies for avoiding contact with the virus were developed, and early diagnosis and support therapy were recommended to reduce mortality due to the disease.

Three "mystery diseases" (unnamed for the students, but based on HPS, Lyme disease, and Lassa fever) are the initial focus of this activity. HPS was first recognized in 1993; Lyme disease first came to the attention of public health workers in 1975 as an unusual number of cases of juvenile rheumatoid arthritis in children in Lyme, Connecticut; and Lassa fever was first identified in an outbreak in Nigeria in 1969. Cases of HPS were originally clustered in the Four Corners region of the U.S. Southwest, and the majority of cases to date have been found there. Lyme disease is the most commonly diagnosed tick-borne disease in the United States, with the majority of cases clustering in the Northeast, although cases have occurred in 48 of the 50 states. Lassa fever outbreaks occur in west Africa.

Investigating these diseases leads students to recognize that all three of these new diseases "emerged" as a result of environmental changes and/or movement of humans into areas inhabited by the organism that serves as reservoir for the pathogen. The two activities that follow, Activity 3, Superbugs: An Evolving Concern, and Activity 4, Protecting the Herd, help students understand two factors involved in the re-emergence of infectious diseases.

Materials and Preparation

You will need to prepare the following materials before conducting this activity:

To make investigation files, copy Masters 2.2, 2.3, and 2.4 and assemble them into file folders that you label "Physician's File," "Laboratory Scientist's File," and "Field Researcher's File." You may want to use a different-colored folder for each type of file. Make enough sets of these files so that no more than three or four students (one student from each of three or four different teams) study the documents in the file together. For example, for a class of 30 students (10 teams), prepare three sets of each type of file.

Procedure

1. Introduce the activity by asking students to suppose that a friend developed a strange rash and then a fever accompanied by severe vomiting and diarrhea. Their friend was hospitalized for a week before finally recovering. Then, they hear about a student in another class who had similar symptoms, and they learn that this student's cousin was also sick with fever, vomiting, and diarrhea. A few days later, they hear a television report about a strange illness affecting five students at a nearby high school. The symptoms described sound just like those experienced by their friend. Ask students to suggest questions they might ask about how to protect themselves from this illness. Write these questions on the board or a transparency.

If students ask, explain that the symptoms do not indicate a particular disease, but are used to get students thinking. Complete this step quickly, accepting and listing four or five reasonable questions from students, such as, "Do all the sick people have the same disease?" "What is the cause of the disease?" and "Do the victims have anything in common that can tell us how the disease is transmitted?" It is important to leave these questions on the board or the overhead projector so that students can refer to them as they complete the activity.

2. Tell students that public health officers are responsible for answering these types of questions when a cluster of unusual cases of disease occurs. Explain that in this activity students will follow in the footsteps of public health officers to answer some of the questions they have listed about a mystery disease. Distribute a copy of Master 2.1, Three Mysterious Diseases, to each student and ask four volunteers to read the script to the class.

If you have students who are interested and talented in drama, you may want to give them the scripts the previous day and ask them to read them dramatically to the class.

If students ask what you mean by "unusual cases of disease," explain that it could mean a variety of unexpected occurrences including symptoms that are rare in general, symptoms that are rare in the population in which they are now occurring, or unusual severity of illness or fatality rates.

You can use the Mystery Diseases video on the Web site to introduce the activity if you have the equipment to project the video for the whole class.

3. Organize students in teams of three and tell them they will spend the next 30 minutes investigating the first mystery disease. Direct them to assign each team member one of the following roles: physician, laboratory scientist, or field researcher. Explain that each of these experts will look for clues that will help his or her team answer the questions the class listed in Step 1.

We suggest that you use the same teams as in Activity 1.

4. Identify stations in the room that have investigation documents for the physicians, laboratory scientists, and field researchers. Distribute one copy each of Master 2.5, Notes from the Physician's Investigation; Master 2.6, Notes from the Laboratory Scientist's Investigation; and Master 2.7, Notes from the Field Researcher's Investigation to each team. Direct students to go to the appropriate station and review and discuss the clues they find there about the disease with their colleague "experts" from the other teams. Ask them to record significant information on the forms you distributed. Tell students they will have 15 to 20 minutes to complete their research.

Move among the groups during this time, answering their questions and using probing questions to direct their attention to significant details in their information. Students in the field researcher groups may wonder why there is no Interview Transcript from "J. McDonald." Draw their attention to the "Other Comments" on McDonald's "Investigation of Victim's Home" report, in which she indicates that the victim's mother and aunt refused to be interviewed.

assessmentCollect students' Final Reports and review them to evaluate how well students were able to identify the evidence that supported or refuted a claim about the disease. Identify areas where students could improve and discuss them with the class when you return their papers.

Tip from the field test. To save time and reduce confusion, place three or four copies of Masters 2.3, 2.6, and 2.7 at the appropriate stations prior to class time. Then tell students they will find a copy of the form they need to complete at the station.

5. Reconvene the original teams and distribute one copy of Master 2.8, Mystery Disease 1 Final Report, to each student. Allow students 10 minutes to pool their information and complete the report form.

Again, move among the groups, answering their questions and directing their attention to significant details. Students may have particular difficulty with the final task, which asks whether the disease is emerging, re-emerging, or endemic. Help them come to the conclusion that this is an emerging disease by asking questions such as, "Was there evidence that this disease is common in the Southwest?" "Was there evidence that it was not one of these common diseases?" "What did you decide was the cause of the disease?" "Has this infectious agent been known to cause a disease with the ARDS symptoms?" and "What is the evidence that this is an 'old' disease? . . . that it is a 'new' disease?"

6. Distribute Master 2.9, Mystery Disease 2 Final Report, to half the teams and Master 2.10, Mystery Disease 3 Final Report, to the remaining half. Explain to students that a group of experts similar to those in their teams pooled information from their investigations to complete these reports. Ask students to study the report forms while you distribute one copy of Master 2.11, Mystery Diseases Summary Table, to each student.

7. Direct students to complete the table on Master 2.11 for the two diseases for which they have report forms.

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