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AIDS
"When a butterfly flutters its wings in one part of the world,
it
can eventually cause a hurricane in another."
~
from Edward Lorenz and Chaos Theory
HIV/AIDS Explained
AIDS
(Acquired Immuno Deficiency
Syndrome) is one of the
worst pandemics the world has ever known. HIV
(Human Immunodeficiency
Virus), the virus that
causes AIDS, was first discovered in 1981 in a remote area of Central Africa. It
has since swept across the globe, infecting millions in a relatively short
period of time.
AIDS has
killed more than 30 million people that we know of,
with up to 3.6 million people dying in 2005 alone . While many
cases go unreported, the prevalence of the disease is increasing.
By
comparison:
- The flu
pandemic of 1918 killed approximately 20 million people worldwide.
- World
War II killed approximately 40 million people.
Clearly the
AIDS pandemic has had, and will continue to have, a significant and global
impact.
The thought
of contracting HIV is frightening. And there is good reason for that fear -- the
disease is presently incurable, it has a high mortality rate, it spreads quickly
and there is no vaccine to protect against it. In today's world, that
combination is rare. For example, smallpox is often fatal, but the
disease has been completely contained through vaccinations. Tuberculosis
is often fatal but can usually be cured with antibiotics if caught early.
AIDS has
been able to infect and kill so many people because of its unique makeup. Let's
look at some of the features that make this disease so unusual:
- HIV
spreads by intimate contact with an infected person. Forms of intimate
contact that can transmit AIDS include sexual activity and any sort of
situation that allows blood from one person to enter another. Especially
when you compare it with the many viruses that spread through the air, it
would seem like the intimacy involved in the transmission of AIDS would be a
limiting factor. However
- A person
can carry and transmit the HIV virus for many years before any symptoms show
themselves. A person can be contagious for
a decade or more before any visible signs of disease become apparent.
In a decade, a promiscuous HIV carrier can potentially infect dozens of
people, who each can infect dozens of people, and so on.
- HIV
invades the cells of our immune system and reprograms the cells to become
HIV-producing factories. Slowly, the number of immune cells in the body
dwindles and AIDS develops. Once AIDS manifests, a person is susceptible to
many different infections, because the immune system has been weakened so
much by the HIV it can no longer fight back effectively. HIV has also shown
the ability to mutate, which makes treating the virus nearly impossible.
-
HIV invades and destroys the immune system -- the system
that would normally protect the body from a virus. HIV corrupts and disables
the system that should be guarding against HIV.
Photo
courtesy National Institute of Allergy and Infectious Diseases
HIV, the virus that causes AIDS, is shown budding out of a human immune
cell.
Unprotected sex is the most common way of transmitting HIV.
Your chances for
infection increase with each new partner. Here is a list of ways in which
HIV can be transmitted:
- Sexual contact
- Sharing contaminated intravenous needles
- Breastfeeding (mother to baby)
- Infected mother to foetus during pregnancy or birth
- Blood transfusions (Rare in countries where blood is screened for
HIV antibodies.)
There is
also a slight chance of transmission through open-mouth kissing and biting.
However, there have been very few cases of HIV being transmitted through
either method.
HIV does
not transmit through the air or surface contact like cold and flu viruses do.
HIV is a fragile virus and doesn't survive well outside the human body. This
fragility makes the possibility of environmental transmission very remote.
Outside of a host cell, HIV doesn't survive for very long. Once the fluid
(blood, sweat, tears, et cetera) containing the HIV virus dries, the risk of
environmental transmission is nearly zero.
There is
a lot of misinformation about how HIV can be transmitted. Here is a list of ways
in which HIV is not transmitted:
- Saliva, tears and sweat
- Saliva and tears contain only small
amounts of HIV, and scientists haven't detected any HIV in the sweat of
an infected person.
- Insects - Studies show no evidence of HIV transmission through
bloodsucking insects. This is true even in areas where there are many
cases of AIDS and large populations of mosquitoes.
- Using the same toilet seat
- Swimming in the same pool
- Touching, hugging or shaking hands
- Eating in the same restaurant
- Sitting next to someone
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The
HIV Life Cycle
Like all
viruses, HIV treads the fine line that separates living things from
non-living things. Viruses lack the chemical machinery that human cells
utilize to support life. So, HIV requires a host cell to stay alive and
replicate. To replicate, the virus creates new virus particles inside a host
cell and those particles carry the virus to new cells. Fortunately the virus
particles are fragile.
Viruses,
like HIV, don't have cell walls or a nucleus. Basically, viruses are made up
of genetic instructions wrapped inside a protective shell. An HIV virus
particle, called a virion, is spherical in shape and has a diameter
of about one 10,000th of a millimeter.
HIV
infects one particular type of immune system cell. This cell is called the
CD4+T cell, also know as a T-helper cell . Once infected, the T-helper cell
turns into a HIV-replicating cell. T-helper cells play a vital role in the
body's immune response. There are typically 1 million T-cells per one
milliliter of blood. HIV will slowly reduce the number of T-cells until the
person develops AIDS.
To
understand how HIV infects the body, let's first look at the virus's basic
structure. Here are the basic parts of the HIV virus:
- Viral envelope - This is the outer coat of the virus. It is composed
of two layers of fatty molecules, called lipids. Embedded in the
viral envelope are proteins from the host cell. There are also about 72
copies of Env protein, which protrudes from the envelope surface.
Env consists of a cap made of three or four molecules called glycoprotein (gp) 120, and a stem consisting of three to four
gp41 molecules.
- p17 protein - The HIV matrix protein that lies between the envelope
and core
- Viral core - Inside the envelope is the core, which contains 2,000
copies of the viral protein, p24. These proteins surround two
single strands of HIV RNA, each containing a copy of the virus's nine
genes. Three of these genes -- gag, pol and env -- contain information
needed to make structural proteins for new virions.
HIV is a
retrovirus, which means it has genes composed of ribonucleic acid
(RNA) molecules. Like all viruses, HIV replicates inside host cells. It's
considered a retrovirus because it uses an enzyme, reverse transcriptase,
to convert RNA into DNA.
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What
HIV Does
Once the
HIV virus enters the body, it heads for the lymphoid tissues, where it finds
T-helper cells.
How the
HIV virus infects immune system cells and replicates:
- Binding - The HIV attaches to the immune cell when the
gp120 protein of the HIV virus binds with the CD4 protein of the
T-helper cell. The viral core enters the T-helper cell and the virion's
protein membrane fuses with the cell membrane.
- Reverse transcription - The viral enzyme, reverse
transcriptase, copies the virus's RNA into DNA.
- Integration - The newly created DNA is carried into the
cell's nucleus by the enzyme, viral integrase, and it
binds with cell's DNA. HIV DNA is called a provirus.
- Transcription - The viral DNA in the nucleus separates
and creates messenger RNA (mRNA), using the cell's own
enzymes. The mRNA contains the instructions for making new viral
proteins.
- Translation - The mRNA is carried back out of the
nucleus by the cell's enzymes. The virus then uses the cell's natural
protein-making mechanisms to make long chains of viral proteins and
enzymes.
- Assembly - RNA and viral enzymes gather at the edge of
the cell. An enzyme, called protease, cuts the
polypeptides into viral proteins.
- Budding - New HIV virus particles pinch out from the
cell membrane and break away with a piece of the cell membrane
surrounding them. This is how enveloped viruses leave the cell. In this
way, the host cell is not destroyed.
No one
dies from AIDS or HIV specifically. Instead, an AIDS-infected person dies
from infections, because his or her immune system has been dissipated. An
AIDS patient could die from the common cold as easily as he or she could
from cancer. The person's body cannot fight off the infection, and he or she
eventually dies.
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HIV/AIDS History
-
1926-46
- HIV possibly spreads from monkeys to humans. No one knows for
sure.
-
1959
- A man dies in Congo in what many researchers say is the first
proven AIDS death.
-
1981
- The Centres for Disease Control and Prevention (CDC) notices
high rate of otherwise rare cancer
-
1982
- The term AIDS is used for the first time, and CDC defines it.
-
1983/84
- American and French scientists each claim discovery of the
virus that will later be called HIV.
-
1985
- The FDA approves the first HIV antibody test for blood
supplies.
-
1987
- AZT is the first anti-HIV drug approved by the FDA.
-
1991
- Basketball star Magic Johnson announces that he is
HIV-positive.
-
1996
- FDA approves first protease inhibitors.
-
1999
- An estimated 650,000 to 900,000 Americans living with
HIV/AIDS.
-
2002
- AIDS global death toll reaches nearly 28.1 million.
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§
World
Impact
To understand
the devastation of AIDS, you have to understand the high mortality rate of
people who develop the disease. If you counted every person in the city of
Chicago, which is about 3 million, you would get an idea of how many people died
worldwide from AIDS each year for the past few years. Basically, that means that
each year AIDS kills the same number of people that populate the third largest
city in the United States.
Between 36.7
and 45.3 million people are infected with the HIV virus worldwide as of November
2005, with as many as 25.8 million of those cases in sub-Saharan Africa.
Additionally, another 4.9 million new HIV infections occurred in 2005, which
represents almost 14,000 new cases per day.
The regions
with the greatest number of people living HIV/AIDS, according to the World
Health Organisation, include:
-
Sub-Saharan Africa - 25.8 million
- South
and Southeast Asia - 7.4 million
- Latin
America - 1.8 million
- North
America - 1.2 million
-
Eastern Europe/Central Asia - 1.6 million
AIDS is
clearly one of the worst health crises facing the world today. Without any truly
effective treatment, most health experts are putting an emphasis on prevention
to stop the spread of HIV.
The newly replicated virions will infect other T-helper cells and
cause the person's T-helper cell count to slowly dwindle. The lack of T-helper
cells compromises the immune system. When a person's T-helper cell count drops
below 200,000 cells per one milliliter of blood, he or she is considered to have
AIDS. The development of AIDS takes about two to 15 years, but about half of all
people with HIV will develop AIDS within 10 years after becoming infected.
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Our remedies oft
In ourselves do lie
~ William Shakespeare~
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