origins of hiv dr. matthew marsden, ph.d. ucla school of medicine

Origins of HIVDr. Matthew Marsden, Ph.D.

UCLA School of Medicine

http://www.ck12.org/concept/HIV/

On http://aids.gov/hiv-aids-basics/hiv-aids-101/aids-timeline/

A new disease…

• What is HIV?

• What is the difference between a virus and a bacteria?

• How is HIV transmitted?

• 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?

http://pathmicro.med.sc.edu/lecture/hiv9.htm

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.

http://aids.gov/hiv-aids-basics/hiv-aids-101/what-is-hiv-aids/

What is HIV?

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.

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?


Viruses are:


Can only replicate in living cells - Some can survive for long periods of time outside cells, but cannot replicate that way.

What is HIV?


Viruses are:


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

Structures: DNA and RNA floating freely in cytoplasm. Cell wall and cell membrane

DNA or RNA enclosed inside a coat of protein

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

http://www.diffen.com/difference/Bacteria_vs_Virus

http://pathmicro.med.sc.edu/mhunt/vir-size.jpg

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

Virus

Bacterium

Image modified from: http://www.oucom.ohiou.edu/dbms-witmer/tarbosaurus_skull.htm

Relative size:

http://www.oucom.ohiou.edu/dbms-witmer/tarbosaurus_skull.htm

http://tcf.epfl.ch/page-20833-en.html

The HIV genome is composed of 9 genes, which encode 15 proteins.

For comparison, the E. Coli bacterium contains around 4,377 genes and the human genome encodes around 21,000 genes.

http://biology.kenyon.edu/slonc/gene-web/Lentiviral/Lentivi2.html

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).


HIV is a virus that infects and destroys cells of the immune system (CD4+ cells).

Approximately 8-10 years

Initial infectionAsymptomatic period

(clinical latency)AIDS

Often (not always) accompanied by severe flu like symptoms: 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.niaid.nih.gov/topics/HIVAIDS/Understanding/Biology/pages/clinicalcourse.aspx

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

http://preprod.www.tibotec.com/content/backgrounders/www.tibotec.com/hiv_lifecycle.html

• 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://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.avert.org/hiv-types.htm

HIV “family tree”

Where did HIV come from?

http://what-when-how.com/medical-microbiology-and-infection/zoonoses-systemic-infection/

Zoonosis = Cross-species transmission event

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

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.






http://www.awf.org/content/wildlife/detail/chimpanzee

HIV-1 group M, which is the most prevalent HIV strain, jumped from chimpanzees into humans.



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

HIV-2 originated in sooty mangabeys and is responsible for fewer infections than HIV-1

New viruses are still being transferred from primates to humans, and have the potential to cause new diseases and epidemics.

http://pin.primate.wisc.edu/factsheets/entry/sooty_mangabey

Origins of human AIDS viruses.



Geographic distribution of SIVcpz and SIVgor infections in sub-Saharan Africa.



HIV-1 origins.



HIV-1 origins.



Likely independent transmission events into humans

HIV-2 origins.



HIV-2 origins.



Likely independent transmission events into humans

When did HIV first jump into humans?

M Worobey et al. Nature 455, 661-664 (2008) doi:10.1038/nature07390

Maximum clade credibility topology inferred using BEAST v1.4.7 under a Bayesian skyline plot tree prior.

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:


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!

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origins of hiv dr. matthew marsden, ph.d. ucla school of medicine

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