patient zero: the origins, risks, and prevention of emerging diseases

Patient Zero: The Origins, Risks, and Prevention of Emerging

Diseases

Based on the Radiolab episode “Patient Zero”with animations from HHMI Holiday Lectures

byAndrew E. Lyman-Buttler

The International School of Minnesota, Eden Prairie, MN

1. Explain how the molecular clock can act as a “tape measure” of evolution.

2. Describe how emergent diseases can spread into human populations.

3. Evaluate the effects of social and cultural factors in the transmission and understanding of disease.

4. Explain how the molecular biology of HIV allows it to infect target cells.

5. Discuss the mechanisms of viral recombination, and explain its role in the emergence of new diseases.

6. Describe one strategy for the prevention of new pandemics.

7. Outline the steps of the HIV reproductive cycle.

Learning Objectives

2

A new and deadly disease has emerged, causing symptoms unlike anything ever seen before…

1.As a class, list all the possible causes of disease.2.Some diseases are transmissible from person to person. List all the ways this might happen.3.Epidemiologists can’t do controlled experiments on human subjects (i.e., purposefully exposing people to suspected disease-causing agents).

a. How can they determine the cause of a disease? b. How can they figure out whether it’s transmissible?c. If it is, how can they determine the mode of

transmission?

Part I – An Emerging Disease

3

An emergingpandemic…

4

Play Audio 10:00 to 6:04

http://www.radiolab.org/2011/nov/14/aids/

5

View the following animation (4:52) from the Howard Hughes Medical Institute that shows how HIV infects a cell and replicates itself using reverse transcriptase and the host's cellular machinery:

http://www.hhmi.org/biointeractive/disease/hiv_life_cycle.html

HIV reproductive cycle

The molecular clock

6

Play Audio 26:04 to 10:04

1. How does the molecular clock allow us to determine the approximate time of origin of a virus?

2. What other viral infections have you heard of that can infect other animals in addition to humans?

3. Why do you think these viruses are so alarming to public health officials?

Part II – Spillover

7

Spillover of influenza

View the following video lecture clip (1:18) on the origins of influenza virus strains.

http://media.hhmi.org/hl/99Lect4.html?start=29:02&end=30:21

8

Spillover of HIV

9

Play Audio 310:04 to 15:02

1. How was the world changing in 1908?

2. How might these conditions be relevant to the spread of an infectious disease?

Part III – Why Then?

10

Recombination

11

Scanning electron micrograph of HIV-1 (in green) budding from cultured lymphocyte. Multiple round bumps on cell surface represent sites of assembly and budding of virions.

Play Audio 415:02 to 24:20

Recombination (example based on influenza virus)

View the following animation (3:05) from the Howard Hughes Medical Institute that shows how two different strains of influenza can infect a single cell to produce a new third strain of influenza:

http://www.hhmi.org/biointeractive/disease/recombination.html

12

1. How can non-human animals provide a pathway for new viruses to enter the human population?

2. Consider the emergence of a pandemic, from the first spillover event to worldwide transmission. Where are the points at which we could stop the spread of the disease? Which point would be easiest?

Part IV – Prevention

13

Preventing the next pandemic

14

Play Audio 524:20 to end

1. Explain how the molecular clock can act as a “tape measure” of evolution.

2. Describe how emergent diseases can spread into human populations.

3. Evaluate the effects of social and cultural factors in the transmission and understanding of disease.

4. Explain how the molecular biology of HIV allows it to infect target cells.

5. Discuss the mechanisms of viral recombination, and explain its role in the emergence of new diseases.

6. Describe one strategy for the prevention of new pandemics.

7. Outline the steps of the HIV reproductive cycle.

You should now be able to:

15

1. Abumrad, J., and Krulwich, R. "Patient Zero: The Cell That Started a Pandemic." Radiolab. 14 November 2011. WNYC. http://www.radiolab.org/2011/nov/14/aids/

2. Social network diagram (Slide 4): FMS - Sentinel Visualizer, http://www.fmsasg.com, used with permission.

3. Howard Hughes Medical Institute 2007 Holiday Lectures: AIDS: Evolution of an Epidemic. DVD.

4. Howard Hughes Medical Institute 1999 Holiday Lectures: 2000 And Beyond: Confronting the Microbe Menace. DVD.

5. Diagram on Slide 7 & phylogeny on Slide 10: Hillis, David. "The Unexpected Practical Applications of Evolutionary Biology." National Association of Biology Teachers Conference. Hyatt Regency Hotel, Dallas, TX. 2 November 2012. Lecture. Used with permission.

6. Scanning electron micrograph of HIV-1 budding (in green) from cultured lymphocyte: C. Goldsmith, CDC. http://phil.cdc.gov/phil/details.asp?pid=10000

7. Africa 1908 map (Slide 11): Hemispheres Antique Maps & Prints. From Rand McNally's Indexed Atlas of the World, 1908. http://www.betzmaps.com

8. Slide 15 images: Global Viral Forecasting Initiative: http://globalviral.org/

References/Media Credits:

16