Infectious Diseases: Unit 2

What does it mean to be an infectious disease?

In Unit 1, the students learned that infectious agents like bacteria, viruses, and parasites can cause infectious diseases. Students also saw that infectious diseases have wide reaching impacts on both individuals and society. Now we are going to focus on how infectious diseases are identified. Contrary to popular belief, determining that a disease is caused by an infection is surprisingly difficult and we are still discovering new infectious diseases today!

Lesson 1

Infectious Disease Detectives — Typhoid Mary?

This lesson reinforces the concept that infectious diseases are caused by pathogens, and that although identifying the pathogen may be difficult it is important for treatment and/or prevention. The lesson also emphasizes that being able to identify infectious agents is a relatively new skill, largely because identification usually requires special tools, for example microscopes.

Objectives – Explain how to identify disease as infectious.
– Explain how to determine source of an infectious disease.
Activities Typhoid Mary video
Materials Printed Materials:
– Lesson worksheet

– Video (see PPT)
Homework Paragraph on historical quarantine.

Lesson 2

What are the patterns of infectious disease?

Continuing on from Lesson 1, this lesson emphasizes that being able to identify infectious microbes is a relatively new skill. This is largely because microbes are very small, flora and pathogens ‘look’ the same, and the infectious microbes may be hard to isolate. The two major advances described here are microscopy and culturing. This lesson also emphasizes that our understanding of infectious diseases is continually evolving.

Objectives – Explain why it was hard to identify source of infectious disease prior to germ theory.
– Explain where microbes come from.
– Describe why viruses pass through bacterial filters.
Activities Ghost map
Materials Printed Materials:
– Lesson worksheet
Homework Research environmental habitat with no microbes.

Lesson 3

How do infectious diseases spread?

This lesson has two goals. First, it aims to directly expose students to the difficulty of identifying an infectious agent and its source. A second goal is to lead students to understand the importance of vaccination in preventing the spread of infectious diseases. It also briefly introduces Koch’s postulates, which are the focus of Lesson 4.

Objectives – Explain process by which disease spreads.
– Explain effects of vaccination on disease spread.
Activities Spread simulation.
Materials Printed Materials:
– Lesson worksheet

Simulation Materials:
– Boiled starch
– Iodine as indicator
– Small plastic cups (numbered)
– Water
Homework Does typhoid fever fulfill Koch’s postulates?

Lesson 4

How can we prove infection causes disease?

This lesson has two purposes: It introduces the principle of causation and the important difference between correlation and causation. The second goal is to explore possible challenges/limitations to fulfilling each postulate and hence proving causation.

Objectives – Define Koch’s postulates.
– Apply Koch’s postulates to investigations of infectious diseases.
– Describe limitation of postulates.
Activities Modeling of Koch’s postulates with cholera.
Materials Printed Materials:
– Lesson worksheet
Homework Ulcer case study (reading in Lesson 2.4 is crucial).

Lesson 5

Do bacteria cause stomach ulcers? Applying Koch’s postulates

The main purpose of this lesson is to provide students an opportunity to practice experimental design, predict results, and interpret data. It also aims at solidifying their understanding of the complexities involved in proving that an infectious microbe causes a disease.

Objectives – Explain limitations of Koch’s postulates.
– Design an experiment to test the hypothesis that an infectious agent is the cause of a disease.
– Predict and interpret the experimental results relat-ing to the hypothesis.
Activities Ulcer case study
Materials Printed Materials:
– Lesson worksheet
– Unit quizzes
Homework Study for the Unit 2 quiz.

Teacher Prep: Unit 2 Lesson Videos

In the YouTube embed below, click the order listing in the upper right to toggle the display for the full playlist.