Infectious Diseases: Unit 3

When does a microbe become pathogenic?

Up until now we have focused on identifying infectious diseases. In this unit we turn our focus to the question: When does a microbe become pathogenic? At the heart of this question is the idea that most microbes are not pathogenic. For example, we live in a microbe -filled world but we are rarely sick. This unit will address questions like: Can any microbe be pathogenic under the right circumstances? Are the same microbes pathogenic in all hosts? What is the difference between a pathogen and a microbe?

Lesson 1

The zoo in you — our microbial ecosystem and Ebola

To this point we have focused on infectious diseases, and in the first unit we briefly discussed immune barriers that protect use from pathogenic microbes. However, we interact with microbes all the time without getting disease. So when does a microbe become pathogenic? This lesson begins to explore the circumstances and virulence factors that lead to pathogenicity. And emphasizes the idea that pathogenicity is a dynamic host-microbe interaction.

Objectives – Describe three properties of pathogenic microbes.
– Define virulence, micro-biota, and microbiome.
– Give one example of how a microbe can be a pathogen in one host but not in another.
Activities – TED talk
– Ebola video
Materials – Printed Materials:
– Lesson worksheet

– Videos (see PPT)
Homework Prep for Jigsaw activity (Lyme and malaria readings)

Lesson 2

Reservoirs and vectors — Lyme disease and Malaria

In this lesson we will explore reservoirs and vectors by looking at the life cycles of two socially important diseases, malaria and Lyme disease. For microbes to exist they must have a reservoir, which may be humans or other animals. A reservoir is central to the microbe’s life cycle, and generally carries the microbe long enough to transmit it to another host. Sometimes humans are infected ‘unintentionally’ by pathogens, and although they cannot complete their life cycle in humans they cause disease. We will also see that microbes utilize vectors, usually insects, to bypass a key host barrier, the skin!

Objectives – Role and example of reservoirs in a pathogen’s life cycle.
– Role and example of vectors in pathogen’s life cycle.
– Describe preventative measures to limit spread of Lyme disease and malaria.
Activities Jigsaw on malaria and Lyme disease.
Materials Printed Materials:
– Lesson worksheet
– Jigsaw reading
Homework Two paragraphs describing the life cycle of final project pathogen.

Lesson 3

Invasion of the body snatchers — the War Card Game

Lesson 3.1 introduced the concept that the host has immune system barriers to protect against pathogens and that these barriers have to be bypassed if the pathogen is going to infect successfully. This lesson illustrates the close and constantly evolving relationship between a pathogen and the body. For instance, the host has evolved numerous ways to separate its sterile inner body from the environment; hence, a successful pathogen itself needs to evolve specific tools, adaptations, to infect the host.

Objectives – Give two examples of virulence factors.
– Describe symptoms of two new infectious diseases.
Activities War card game
Materials Printed Materials:
– Lesson worksheet
– Card deck
– Unit quizzes
Homework – Worksheet: war card reflection
– Study for Unit 3 quiz.

Teacher Prep: Unit 3 Lesson Videos

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