Human Immunodeficiency Virus

Acquired Immune Deficiency Syndrome

2005-2006

Measles

Polio

Hepatitis

Chicken pox

2005-2006

30-40 million deaths world-wide

RNA virus

 Eradicated in 1976   vaccinations ceased in 1980   at risk population?

2005-2006

 Viruses that “jump” host   switch species   Ebola, SARS, bird flu, hantavirus

SARS

Ebola hantavirus

2005-2006

 DNA or RNA enclosed in a protein coat  Viruses are not cells  So…they are not alive  Extremely tiny

  electron microscope size   smaller than ribosomes   ~20–50 nm

2005-2006

1st discovered in plants (1800s)  tobacco mosaic virus

  A package of genes in transit from one host cell to another

  Most viruses carry their own DNA

  DNA (genes) RNA Proteins

  These proteins form antigens and new viruses that then further invade the body

bacteriophage influenza

“A piece of bad news wrapped in protein”

– Peter Medawar

 Lipid bilayer membranes surrounding a viral capsid   envelopes are derived from host cell

membrane (so it is slightly disguised)   glycoproteins on surface

HIV

 Retroviruses   have to copy viral RNA into host DNA

  enzyme = reverse transcriptase   RNA → DNA → mRNA

  host’s RNA polymerase now transcribes viral DNA into viral mRNA   mRNA codes for viral components   host’s ribosomes produce new viral proteins

Why is this significant?

protein RNA DNA

transcription translation

replication

  HIV stands for Human Immunodeficiency Virus

  While most viruses carry DNA, HIV is a RETROVIRUS which means it carries 2 strands of RNA instead of DNA

  Contains an envelope with glycoproteins for binding to specific receptor

  As well as 2 copies of reverse transcriptase!

  When RNA is copied to DNA, it can get kind of messy…

  This allows for many mutations in HIV *BUT IS THIS A GOOD THING?

The first ever photo of HIV

  Envelope binds to host cell membrane and capsid released

  HIV enters host cell:   macrophage & CD4 T Cells   reverse transcriptase synthesizes

double stranded DNA from viral RNA   high mutation rate

  Transcription produces more copies of viral RNA   translated into viral proteins   proteins & viral RNA self-assemble

into virus particles   released from cell by “budding”

 Imagine the immune system is like FREMONT HIGH SCHOOL

 Our Helper T-Cells are like the Security Guards (“Charlies”)

 Now, these Security Guards never see each other, but they communicate using walkie talkies

 They communicate with each other to make sure the campus is safe

 But now imagine these security guards have been infected by a virus, and are no longer on campus…

Kaposi Sarcoma – a rare form of cancer and one of the leading causes of HIV/AIDS related deaths…

  AIDS stands for Acquired Immune Deficiency Syndrome

  People develop AIDS because HIV has damaged too many of their CD4+ cells (they have less than 200 per cubic millimeter)

  Before getting AIDS, a person usually goes through 3 phases in the PROGRESSION OF HIV:

1.  Primary Infection (several weeks of the flu)

2.  Asymptomatic phase (up to 10 years with no real health problems)

3.  Symptomatic phase (opportunistic infections begin to occur)

4.  AIDS (T-Cell count low, severe health problems)

 At present in the US and UK, an AIDS DIAGNOSIS is confirmed if a person with HIV develops one or more of a specific number of severe opportunistic infections or cancers

 Can you see on the graph where a person has been diagnosed with AIDS?

 It is possible for someone to be very ill with HIV but not have an AIDS diagnosis.

  HIV is a descendent of African SIV (simian chimpanzee immunodeficiency virus), but how did it get transferred to humans?

  1. The “Hunter” Theory:   SIV was transferred as a result of chimps being killed and eaten or their

blood getting into cuts or wounds on the hunter   Normally the hunter's body would have fought off SIV, but on a few

occasions it adapted itself to its new human host   2. The Oral Polio Vaccine (OPV) theory:

  Many believe that HIV can be traced to the testing of an oral polio vaccine called Chat, given to about a million people in the Belgian Congo and Ruanda in the late 1950s.

  To be reproduced, live polio vaccine needs to grow in living tissue, and Chat was grown in kidney cells taken from local chimps infected with SIV

  This would cause contamination of the vaccine with chimp SIV, and a large number of people subsequently becoming infected with an adapted form of SIV HIV

However, the OPV theory has been shot down due to insufficient evidence to cause infection in most people, SIV/HIV needs to get directly into the bloodstream to cause infection (BUT this was an oral vaccine)