Infectious DiseasesUnit 2 Lesson 4 plan

Do Now

• What is the difference between correlation and causation?

• How could you prove causation?

Robert Koch – connecting the dots to disease

Bacillus anthracis

Identifying the infectious agent –

Koch’s postulates

1. Association – It must always be present in every case – but not in healthy animals.

2. Isolation – It must be isolated from the sick animal into pure culture.

3. Causation – The pure microbe must cause the disease in a healthy animal.

4. Re-isolation - When the microbe is re-isolated from the sick animal it must be the same as the original.

Applying Koch’s postulates to cholera!

1. Association – It must always be present in every case – but not in healthy animals. 2. Isolation – It must be isolated from the sick animal into into pure culture.

3. Causation – The pure microbe must cause the disease in a healthy animal.

4. Re-isolation - When the microbe is re-isolated from the sick animal it must be the same as the original.

Sack et al., 2004

Applying Koch’s postulates to cholera!

1. Association – It must always be present in every case – but not in healthy animals.

2. Isolation – It must be isolated from the sick animal into into pure culture.3. Causation – The pure microbe must cause the disease in a healthy animal.

4. Re-isolation - When the microbe is re-isolated from the sick animal it must be the same as the original.

Sack et al., 2004

Vibrio cholera

Applying Koch’s postulates to cholera!

1. Association – It must always be present in every case – but not in healthy animals.

2. Isolation – It must be isolated from the sick animal into into pure culture.

3. Causation – The pure microbe must cause the disease in a healthy animal. 4. Re-isolation - When the microbe is re-isolated from the sick animal it must be the same as the original.

Vibrio cholera

Applying Koch’s postulates to cholera!

1. Association – It must always be present in every case – but not in healthy animals.

2. Isolation – It must be isolated from the sick animal into into pure culture.

3. Causation – The pure microbe must cause the disease in a healthy animal.

4. Re-isolation - When the microbe is re-isolated from the sick animal it must be the same

as the original.

Vibrio cholera

Sack et al., 2004

Wrap up:Sometimes Koch’s postulates

can’t be fulfilled!1. Association – It must always be present in every case – but not in healthy animals*.

2. Isolation – It must be isolated from the sick animal into pure culture**.

3. Causation – The pure microbe must cause the disease in a healthy animal.

4. Re-isolation - When the microbe is re-isolated from the sick animal it must be the

same as the original.

*Typhoid Mary.

**Leprosy or the plague.

• Complete the case study

Homework