Introduction

Have students read the introduction to the module, Introduction to Viruses go “Viral.” The purpose of this reading is to introduce students to the idea that the characteristics of viruses can determine whether an outbreak will emerge and escalate into an epidemic and to inform them of what they will be exploring in the module.

Activity

The purpose of this activity is to determine students’ prior understandings about the differences between an infectious and noninfectious disease (also explored in greater depth in Module 1 – About Infectious Disease) and between an infectious and contagious disease. Using the Disease Chart students identify a specific disease as infectious (I), noninfectious (NI) or contagious (C).

During the discussion students will determine that an infectious disease is a biological disorder caused by microorganisms such as viruses, bacteria and parasites.

A contagious disease is a subset of infectious diseases that are spread from human to human by direct contact or contact with respiratory droplets from infected individuals. Infectious diseases transmitted by food, water, animal or insect vectors are not considered contagious. This distinction becomes important when students explore reproductive rates (R₀) as a factor in the spread of disease.

Materials

One copy of the Disease Chart for each pair or team of students, downloadable below.

Procedure

1. Provide each pair or team of students with one copy of the Disease Chart.
2. Have students label the various diseases as infectious (I), noninfectious (N) and/or contagious (C). Inform them that some diseases will have more than one designation. As they sort they should discuss why they designated a disease in one category or another. Suggest that they record their reasoning for each disease in preparation for class discussion.
3. After they have completed the task have them look for commonalities in the diseases they labeled as contagious.
4. Gather the class together to share their decisions about the category or categories of each disease and the reasoning for identifying a disease as infectious, genetic, or environmental.
5. You may want to write the project the chart and record an “I,” “N,” or “C” next to each disease as groups voice their decisions.
6. Examples of student responses include “Down syndrome is caused by an abnormality in a chromosome and is not caused by an infectious agent so it’s noninfectious”; “measles can be spread when someone coughs and another person breathes in the saliva droplets in the air, so it’s infectious and contagious”; “Polio is caused by viruses in water but can’t be caught from contact with people so it is infectious but not contagious”.
7. For further review, have explore these diseases using the flip cards in the online module..

Disease Chart Answer Key

Discussion

The purpose of this discussion is to have students consider the differences between infectious diseases and noninfectious diseases and what determines whether an infectious disease is considered contagious. The discussion should lead to students to considering the primary modes of transmission of infectious agents and contagious diseases.

You may want to initiate discussion with questions such as:

• What is the difference between an infectious disease and a noninfectious disease?

  Students should recognize that infectious diseases are caused by pathogens such as viruses, bacteria, and parasites and can be spread by direct contact or through vectors. Noninfectious diseases cannot be “caught” from other humans or animals.

• Food poisoning is generally categorized as an infectious disease because it is usually caused by bacteria (such as E. coli or Salmonella). However, you cannot infect other people with your food poisoning as you can infect them with measles. Why are food poisoning and measles both considered infectious diseases? Why is one considered contagious and the other not?

  Both are caused by infectious agents but only measles can be spread by indirect contact with an infected individual. Food poisoning cannot be "caught" by direct or indirect contact with another person with food poisoning.

• Based on the Disease Chart, what are the major modes of transmission for infectious agents? What is the primary mode for contagious diseases?

  The primary modes of transmission for infectious agents include contact with infected individuals, aerosol of infected droplets, food-borne, water-borne and vector borne (such as through insects and animal bites). Students should recognize that contagious diseases are spread from person to person through direct contact with bodily fluids on a person or through sexual encounters. They are also spread by indirect contact through infected droplets in the air that are inhaled or on objects that individuals touch and then enable entry when they touch their mouth or nose.

Post-Discussion Activities

Develop Definitions

Based on the discussion about each kind of disease, have students develop a definition for an infectious disease and contagious disease. Their definitions should demonstrate an understanding that all contagious diseases are infectious diseases but not all infectious diseases are contagious by definition.

Create a Disease

At this point you may want to assess student understanding of viral diseases and what kinds of diseases are contagious. Have students create a fictitious disease that includes the following information:

1. A description of the symptoms of the disease
2. The causative agent, its name and why it has that name (e.g., Ebola virus – named for a river in Africa)
3. Mode of transmission (e.g., direct contact, airborne, foodborne, waterborne, animal/insect vector, animal reservoir)
4. Is it contagious and if so, how contagious is it?

Have students (individuals or small groups) present their fictitious disease with information on a, b and c, and then have the class decide whether the disease is contagious or not and explain their decision.