Emerging & Re-emerging Infectiious Diseases
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Activity 2 - Disease Detectives

8. Display a transparency made from Master 2.11, Mystery Diseases Summary Table, and ask several teams to report one piece of information as you complete the first row of the table. Ask the remaining teams whether they have additional information and whether they disagree with any of the information provided by the other teams. Follow the same procedure for the other two mystery diseases.

Möbius StripThis is a good time to note how technological advances have improved our ability to identify the infectious agents for mysterious diseases. Identification of the spirochete type of bacterium as the cause of Lyme disease required nearly seven years, whereas molecular biology techniques available in 1993 meant that the infectious agent for HPS was identified within a month. Continuing NIAID-supported research on the Lyme disease spirochete has led to improved diagnosis of the disease and the development of a new vaccine to prevent it.

All three diseases are classified as emerging diseases and, although students are not given this information, all three have probably occurred for hundreds if not thousands of years. Nevertheless, only recently have cases occurred in sufficient numbers that they were recognized as specific diseases. The infectious agents for the three diseases are transmitted by:

The environmental factors involved are:

9. Allow students to examine the summary table and then ask them to list any common features they note about the three mystery diseases. Lead a class discussion by asking, "Can you see one overall factor that resulted in the emergence of all three of these diseases?" and "What does this suggest about things people need to consider as we develop land for residential and business purposes?"

Common features of the three mystery diseases, as revealed on Master 2.11, are that all the diseases are emerging, the transmission of the infectious agent involves a nonhuman animal, and environmental factors strongly help explain their occurrence. Guide students to the understanding that environmental and ecological factors, combined with the movement of humans into previously uninhabited areas, help explain the relatively sudden appearance of these "new" diseases.

You may want to reveal the names of the three mystery diseases at this time:

Explain to students that these diseases were first recognized in 1993 (HPS), 1975 (Lyme disease), and 1969 (Lassa fever). Although the symptoms and "clues" presented in the mystery disease cases would immediately implicate HPS, Lyme disease, or Lassa fever if physicians saw them today, in 1993, 1975, or 1969, these three diseases were "new" to health care workers, just as they were to students in this activity.

puzzle pieceIn this step, students are challenged to synthesize in their own words the discussion from Step 9. Completing the sentences requires them to state and elaborate the activity's major concept.

10. Ask students to complete individually, in writing, the sentences at the bottom of Mystery Diseases Summary Table.

11. Collect students' assignments from Step 10 and close the activity by noting several responses (anonymously) and engaging the students in a discussion of the issues that should be considered to avoid or minimize the risks of emerging diseases.

Completing the activity should lead students to recognize that changing environmental conditions create opportunities for new or previously rare diseases to affect large numbers of people. Students are likely to respond to the second question by a blanket statement such as, "People should stay out of uninhabited areas." Challenge them to think more deeply by asking questions such as, "Should you or anyone else be allowed to tell people where they can live?" "What if people in a developing country have an opportunity to dramatically increase their income, as well as their country's productivity, by developing an area previously uninhabited by people? Do the advantages of economic development outweigh the risks of emerging diseases? What do you need to consider to make this evaluation?" and "How might medical and ecological research efforts help resolve these dilemmas?"

You may want to give students the example of the Aswan Dam in Egypt. Schistosomiasis is a disease that causes diarrhea, abdominal pain, and liver problems. Chronic infections may lead to liver failure and may also affect the central nervous system. The disease is caused by a helminth that has a complex life cycle, including stages in both snails and the human bloodstream. Because snails thrive in still waters such as those found in irrigation canals and artificial lakes, the incidence of schistosomiasis frequently increases following construction of dams. Although this was known before the Aswan Dam was constructed, the officials involved in the decision felt that the economic advantages of the dam outweighed the disease consequences. Before the dam was built, about 1 percent of the school children in the area had schistosomiasis. After the dam was built the incidence of schistosomiasis among children in some villages near the artificial lake rose to 100 percent. Since then, Egypt has spent part of the profits from the Aswan Dam on a major, ongoing chemotherapy campaign against schistosomiasis.

This example also shows that the incidence of "old" diseases may be affected by environmental changes. Schistosomiasis is not a "new" disease, but the increased incidence of the disease makes it a candidate for a re-emerging disease. Other factors related to disease re-emergence are explored in the next two activities.

Potential Extensions

Several popular books on emerging infectious diseases make exciting reading and provide further illustration of scientists' work in identifying and limiting the risks of emerging diseases. Assign students to read and report on books such as The Hot Zone by Richard Preston (which describes outbreaks of Ebola hemorrhagic fever) and The Coming Plague by Laurie Garrett (which describes the efforts of scientists and policymakers regarding a variety of emerging and re-emerging diseases, including HPS, Lassa fever, malaria, and Legionnaire disease).

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