Transcript Origins of HIV

http://www.ck12.org/concept/HIV/
Origins of HIV
Dr. Matthew Marsden, Ph.D.
UCLA School of Medicine
A new disease…
On http://aids.gov/hiv-aids-basics/hiv-aids-101/aids-timeline/
• What is HIV?
• What is the difference between
a virus and a bacteria?
• How is HIV transmitted?
http://pathmicro.med.sc.edu/lecture/hiv9.htm
• Basic characteristics of HIV disease course.
• Reasons for the rapid rate of HIV evolution.
• Where did HIV come from?
• When did HIV first jump into humans?
What is HIV?
What is HIV?
To understand what HIV and AIDS are, let’s break it down:
Causative agent:
H – Human – This particular virus can only infect human beings.
I – Immunodeficiency – HIV weakens your immune system by destroying important cells that
fight disease and infection. A "deficient" immune system can't protect you.
V – Virus – A virus can only reproduce itself by taking over a cell in the body of its host.
What is HIV?
To understand what HIV and AIDS are, let’s break it down:
Causative agent:
H – Human – This particular virus can only infect human beings.
I – Immunodeficiency – HIV weakens your immune system by destroying important cells that
fight disease and infection. A "deficient" immune system can't protect you.
V – Virus – A virus can only reproduce itself by taking over a cell in the body of its host.
Disease:
A – Acquired – AIDS is not something you inherit from your parents like eye color.
You acquire AIDS.
I – Immuno – Your body's immune system includes all the organs and cells that work to
fight off infection or disease.
D – Deficiency – You get AIDS when your immune system is "deficient,"
or isn't working the way it should.
S – Syndrome – A syndrome is a collection of symptoms and signs of disease. AIDS is a syndrome,
rather than a single disease. It is a complex illness with a wide range of symptoms.
http://aids.gov/hiv-aids-basics/hiv-aids-101/what-is-hiv-aids/
What is HIV?
Human immunodeficiency virus or HIV is a type of virus
(from the Latin “virus” referring to poison).
Viruses are:
Small
- Generally too small to see with a regular light microscope (20 - 400 nm diameter)
If a cell was a football stadium then a small virus would be around the size of a
football.
What is HIV?
Human immunodeficiency virus or HIV is a type of virus
(from the Latin “virus” referring to poison).
Viruses are:
Small
- Generally too small to see with a regular light microscope (20 - 400 nm diameter)
If a cell was a football stadium then a small virus would be around the size of a
football.
Can only replicate in living cells
- Some can survive for long periods of time outside cells, but cannot replicate that way.
What is HIV?
Human immunodeficiency virus or HIV is a type of virus
(from the Latin “virus” referring to poison).
Viruses are:
Small
- Generally too small to see with a regular light microscope (20 - 400 nm diameter)
If a cell was a football stadium then a small virus would be around the size of a
football.
Can only replicate in living cells
- Some can survive for long periods of time outside cells, but cannot replicate that way.
Made up of Nucleic acids (DNA/RNA) and proteins
-different from protein-only “prions” or nucleic acid-only “viroids”.
Thousands of very different types of virus exist and HIV is a particular type termed a
“retrovirus”.
What is the difference between a virus
and a bacteria?
Bacteria
Virus
Ribosomes:
Present
Absent
Living attributes:
Living organism
Opinions differ on
whether viruses are a form of
life, or organic structures that
interact with living organisms.
Number of cells:
Unicellular; one cell
No cells; not living
Structures:
DNA and RNA floating freely in DNA or RNA enclosed inside a
cytoplasm. Cell wall and cell
coat of protein
membrane
Enzymes:
Yes
Yes, in some
Nucleus:
No
No
Can cause disease?:
Yes
Yes
How is it treated?:
Antibiotics
Vaccines and antiviral
medication.
Reproduction:
Fission- a form of asexual
reproduction
Invades a host cell and takes
over the cell causing it to make
copies of the viral DNA/RNA
and proteins.
Size:
Larger (1000 nm)
Smaller (20 – 400 nm)
Modified from: http://www.diffen.com/difference/Bacteria_vs_Virus
An average virus is much smaller than an average bacterium
Relative size:
http://pathmicro.med.sc.edu/mhunt/vir-size.jpg
An average virus is much smaller than an average bacterium
Relative size:
Bacterium
Virus
Image modified from: http://www.oucom.ohiou.edu/dbms-witmer/tarbosaurus_skull.htm
The HIV genome is composed of 9 genes, which encode 15 proteins.
http://tcf.epfl.ch/page-20833-en.html
http://biology.kenyon.edu/slonc/
gene-web/Lentiviral/Lentivi2.html
For comparison, the E. Coli bacterium contains around 4,377 genes and the human genome
encodes around 21,000 genes.
How is HIV transmitted?
http://aids.gov
Basic characteristics of HIV
disease course.
HIV is a virus that infects and destroys cells of the immune system (CD4+ cells).
http://aids.gov/hiv-aids-basics/hiv-aids-101/what-is-hiv-aids/
HIV is a virus that infects and destroys cells of the immune system (CD4+ cells).
http://aids.gov/hiv-aids-basics/hiv-aids-101/what-is-hiv-aids/
Approximately 8-10 years
Initial infection
Often (not always) accompanied by
severe flu like symptoms:
Asymptomatic period
(clinical latency)
AIDS
Opportunistic infections and cancer:
AIDS (acquired immunodeficiency syndrome) is the late-stage HIV disease. This
occurs when immune system becomes so damaged that it cannot fight off diseases
and certain types of cancer.
Untreated HIV infection is a constant battle between the virus and the host immune system,
with BILLIONS of new infected cells and virus particles produced and cleared EVERY DAY in
each infected person.
http://www.healthhype.com/cd4-count-dropping-viral-load-stable-in-hiv-infection-graph.html
http://www.niaid.nih.gov/topics/HIVAIDS/Understanding/Biology/pages/clinicalcourse.aspx
Reasons for the rapid rate of
HIV evolution.
HIV Life cycle
http://preprod.www.tibotec.com/content/backgrounders/www.tibotec.com/hiv_lifecycle.html
HIV Life cycle
• HIV mutates every time it replicates
• HIV replicates in billions of cells
simultaneously every day
• HIV therefore evolves around 1 MILLION
TIMES faster than mammalian genes
http://preprod.www.tibotec.com/content/backgrounders/www.tibotec.com/hiv_lifecycle.html
Comparison of HIV genetic variation with flu virus (longer lines mean more mutations)
http://www.nature.com/embor/journal/v4/n6s/fig_tab/embor857_F1.html
Comparison of HIV genetic variation with flu virus (longer lines mean more mutations)
http://www.nature.com/embor/journal/v4/n6s/fig_tab/embor857_F1.html
Comparison of HIV genetic variation with flu virus (longer lines mean more mutations)
http://www.nature.com/embor/journal/v4/n6s/fig_tab/embor857_F1.html
Comparison of HIV genetic variation with flu virus (longer lines mean more mutations)
http://www.nature.com/embor/journal/v4/n6s/fig_tab/embor857_F1.html
HIV “family tree”
http://www.avert.org/hiv-types.htm
Where did HIV come from?
Zoonosis = Cross-species transmission event
http://what-when-how.com/medical-microbiology-and-infection/zoonoses-systemic-infection/
Phylogeny of lentiviruses.
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
©2011 by Cold Spring Harbor Laboratory Press
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
Where did HIV come from?
HIV entered the human population from primates, which harbor a related virus known as SIV
(simian immunodeficiency virus). This probably occurred during the butchering and
consumption of monkey meat in Africa.
HIV “family tree”
http://www.avert.org/hiv-types.htm
Where did HIV come from?
HIV entered the human population from primates, which harbor a related virus known as SIV
(simian immunodeficiency virus). This probably occurred during the butchering and
consumption of monkey meat in Africa.
HIV “family tree”
HIV-1 group M, which
is the most prevalent
HIV strain, jumped
from chimpanzees
into humans.
http://www.awf.org/content/wildlife/detail/chimpanzee
http://www.avert.org/hiv-types.htm
Where did HIV come from?
HIV entered the human population from primates, which harbor a related virus known as SIV
(simian immunodeficiency virus). This probably occurred during the butchering and
consumption of monkey meat in Africa.
HIV “family tree”
HIV-1 group M, which
is the most prevalent
HIV strain, jumped
from chimpanzees
into humans.
http://www.awf.org/content/wildlife/detail/chimpanzee
http://www.avert.org/hiv-types.htm
HIV-2 originated in sooty
mangabeys and is
responsible for fewer
infections than HIV-1
http://pin.primate.wisc.edu/factsh
eets/entry/sooty_mangabey
New viruses are still being transferred from primates to humans, and have the potential to
cause new diseases and epidemics.
Origins of human AIDS viruses.
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
Geographic distribution of SIVcpz and SIVgor infections in sub-Saharan Africa.
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
HIV-1 origins.
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
HIV-1 origins.
Likely independent
transmission
events into humans
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
HIV-2 origins.
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
HIV-2 origins.
Likely independent
transmission
events into humans
Sharp P M , and Hahn B H Cold Spring Harb Perspect Med
2011;1:a006841
©2011 by Cold Spring Harbor Laboratory Press
When did HIV first jump into humans?
Maximum clade credibility topology inferred using BEAST v1.4.7 under a Bayesian skyline plot
tree prior.
M Worobey et al. Nature 455, 661-664 (2008) doi:10.1038/nature07390
The strain of HIV responsible for the majority of global infections (HIV-1 Group M) probably
jumped into humans in western Africa sometime between 1884 and 1924.
From there it then spread throughout the world.
Origin and Spread of HIV
Origins of HIV: Major take home points
Different strains of HIV have been independently transmitted into
humans from animals (Chimpanzee, Sooty mangabey, or Gorilla) on
over 10 separate occasions.
The most common strain of HIV (HIV-1, group M), which is
responsible for over 90% of global infections, originated in
chimpanzees (Pan troglodytes).
This likely occurred in Cameroon (West Africa) approximately 100
years ago.
Bushmeat (hunting monkeys for food) is the most likely source of
these transmissions of AIDS viruses into humans.
General References:
Sharp P M , and Hahn B H Cold Spring Harb
Perspect Med 2011;1:a006841
Publication Date: August 1, 2013 | ISBN-10:
0199641145 | ISBN-13: 978-0199641147 | Edition: 1
More References:
1. Hybrid origin of SIV in Chimpanzees Bailes et al.
Science 2003, 300:1713
2. Origins of HIV and the Evolution of Resistance to AIDS.
Heeney et al. Science 2006, 313:462
3. Chimpanzee Reservoirs of Pandemic and Nonpandemic
HIV-1 Keele et al. Science 2006, 313:523
Thank you for your attention!
Questions?