Transcript Case Study: Patient Zero

Patient Zero:
The Origins, Risks, and Prevention of
Emerging Diseases
by
Andrew E. Lyman-Buttler
The International School of Minnesota, Eden Prairie, MN
Based on the Radiolab episode “Patient Zero”
with animations from HHMI Holiday Lectures
Learning Objectives
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.
2
Part I – An Emerging Disease
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.
b.
c.
How can they determine the cause of a disease?
How can they figure out whether it’s transmissible?
If it is, how can they determine the mode of transmission?
3
Play Audio 1
0:00 to 6:04
http://www.radiolab.or
g/2011/nov/14/aids/
An emerging
pandemic…
4
HIV reproductive cycle
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
5
Play Audio 2
6:04 to 10:04
The molecular clock
6
Part II – Spillover
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?
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
Play Audio 3
10:04 to 15:02
Spillover of HIV
9
Part III – Why Then?
1. How was the world
changing in 1908?
2. How might these
conditions be
relevant to the
spread of an
infectious disease?
10
Play Audio 4
15:02 to 24:20
Recombination
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.
11
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
Part IV – Prevention
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?
13
Play Audio 5
24:20 to end
Preventing the next pandemic
14
You should now be able to:
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.
15
References/Media Credits:
1.
2.
3.
4.
5.
6.
7.
8.
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/
Social network diagram (Slide 4): FMS - Sentinel Visualizer,
http://www.fmsasg.com, used with permission.
Howard Hughes Medical Institute 2007 Holiday Lectures: AIDS: Evolution of an
Epidemic. DVD.
Howard Hughes Medical Institute 1999 Holiday Lectures: 2000 And Beyond:
Confronting the Microbe Menace. DVD.
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.
Scanning electron micrograph of HIV-1 budding (in green) from cultured
lymphocyte: C. Goldsmith, CDC. http://phil.cdc.gov/phil/details.asp?pid=10000
Africa 1908 map (Slide 11): Hemispheres Antique Maps & Prints. From Rand
McNally's Indexed Atlas of the World, 1908. http://www.betzmaps.com
Slide 15 images: Global Viral Forecasting Initiative: http://globalviral.org/
16