Infectious Diseases: Unit 4

How do pathogens make us sick?

In the previous unit, we focused on adaptations and situations that contribute to microbes being pathogenic. We emphasized the idea that pathogenicity is a host–microbe interaction and that highly pathogenic microbes have adaptations that make them virulent. In this unit we will explore how an infection leads to symptoms and illness. The students will learn the mechanisms of host cell damage by microbes and how pathogens lead to impairment of host systems via disrupting structure and function.

Lesson 1

Why we feel sick – how pathogens cause direct and indirect damage

This lesson introduces the idea that once pathogens gain access to the host they lead to symptoms by damaging host structures. This damage happens by two main mechanisms: 1) direct damage caused by microbe replication or toxins, 2) indirect damage to infected and bystander host cells caused by the immune response (this will be further focused on in Unit 5). We also explore the idea that where the pathogen is located and how fast it replicates impacts symptoms.

Objectives – Identify symptoms caused by immune response.
– Distinguish between direct and indirect host cell damage.
– Give one example of how intra-cellular and extracellular bacteria lead to host damage and symptoms.
– Give one example of how slow and fast bacterial replication leads to host damage and symptoms.
Activities – Brainstorm symptoms caused by two diseases.
– Discuss the differences between intracellular and extracellular pathogens as well as fast and slow growing ones.
Materials Printed Materials:
– Lesson worksheet
Homework Complete Jigsaw reading about bacterial toxins (Lesson 4.2).

Lesson 2

Toxins – Botox, tetanus, hamburger disease and MRSA

This lesson continues to explore how bacteria cause host damage and symptoms. The last lesson focused on cell damage that results from bacterial replication, this lesson focuses on how bacterial toxins damage the host. Although some toxins damage the host directly, others stimulate immune responses that lead to indirect damage. For example, the LPS that is a component of the bacterial cell wall causes damage by activating innate immune cells. This lesson also emphasizes the importance of toxins for bacterial life cycles.

Objectives – Describe symptoms of three toxin-related diseases.
– Describe how the bacteria use their toxins to infect the host.
Activities Jigsaw activity and teach back.
Materials Printed Materials:
– Lesson worksheet
– Jigsaw reading
Homework Complete Jigsaw table of worksheet.

Lesson 3

How do bacteria adapt to become pathogens? The adaptation auction

The lessons thus far have emphasized that pathogenic bacteria are microbes that find a way to enter the body and cause damage. This is in contrast to most microbes, which are effectively dealt with by the immune system. So that leaves the question: how do bacteria become pathogenic? This lesson will focus on this question from the perspective of adaptations that give bacteria the ability to bypass different levels of the immune system. Many of the adaptations in the auction activity were introduced in Unit 1. In this activity, the focus should be on further understanding the functions of the adaptations from the perspective of gaining accesses to nutrients and causing host cell damage. In addition, the use of the auction is meant to emphasize that having adaptations cost the bacteria energy and other resources, which slows growth.

Objectives – Name adaptations and explain how they benefit bacteria in the right environments.
– Describe how adaptations are used to gain access to nutrients.
– Discuss the limits to acquiring adaptations.
Activities – Discuss microbial adaptations.
– Play adaptation auction activity.
Materials Printed Materials:
– Lesson worksheet
Homework – Complete worksheet.

Lesson 4

How do viruses make us sick – Viral replication

This lesson extends the principles learned in Lesson 4.1 to address how viruses cause host damage. It focuses on how viruses replicate and then exit from host cells. The lesson also introduces the difference between DNA and RNA viruses and explains that viruses need host proteins to replicate. Furthermore, the virus may damage the host cell during replication, either directly or indirectly, as we saw with intracellular bacteria. The activity introduces the viral life cycle in the context of host cell damage. One goal of the discussion is to have students use their knowledge of bacteria-mediated damage to predict how a virus might cause damage.

Objectives – Explain how viral replication leads to host cell lysis.
– Describe the replication of DNA and RNA viruses.
– Explain why RNA viruses carry special enzymes to copy RNA.
– Discuss how viruses cause damage to the host.
– Review viral life cycles in details.
Activities – Discuss how viruses cause damage
– Review viral life cycles
Materials Printed Materials:
– Lesson worksheet
Homework Complete worksheet tables.

Lesson 5

How do viruses adapt? – Antigenic shift and drift and the flu pandemic

This lesson focuses on how viruses mutate quickly to hide from the host’s immune system. In this lesson the students will readdress questions from Unit 1 about the uses and impacts of the flu shot by learning more about the replication of influenza. Like many viruses, influenza has a segmented genome allowing it to share genetic information with other flu viruses. This enables large and fast mutations called shifts, which may be preventable via vaccination. The students will use a hand-on activity to understand the process of antigenic shift and then relate what they learn to flu vaccination.

Objectives – Explain how pathogenic viruses adapt.
– Compare and contrast antigenic drift and shift.
– Relate the concepts of antigenic drift and shift to flu vaccines.
Activities Perform antigenic drift and shift activity.
Materials Printed Materials:
– Lesson worksheet

Activity Materials:
– Clips
– cups
Homework Complete worksheet.

Lesson 6

Designing an antiviral drug – the challenge of HIV

This lesson offers students the chance to apply what they have learned thus far to design an antiviral drug to treat HIV. A video demonstrates a model of how HIV replicates and re-infects a host. The students then use this model to develop their own anti-viral drug targets. Students will then look up real drugs being used to target these pathways, many of which will be aimed at the same targets the students identified!

Objectives – Apply knowledge of viral replication to design drugs against HIV.
– Explain why drug targets are rarely self molecules.
– Explain how multi drug therapies slow the development of drug resistance.
Activities – Video on HIV life cycle
– List structures as potential drug targets.
Materials Printed Materials:
– Lesson worksheet
– Unit quizzes

– Videos (see PPT)
Homework – Research current antiviral drugs and targets.
– Evaluate in-class drug design.
– Study for Unit 4 quiz.

Teacher Prep: Unit 4 Lesson Videos

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