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AIDS - What's new ?
Is the message getting through? We already know enough about AIDS to
prevent its spread, but ignorance, complacency, fear and bigotry continue to
stop many from taking adequate precautions.
We know enough about how the infection is transmitted to protect ourselves
from it without resorting to such extremes as mandatory testing, enforced
quarantine or total celibacy. But too few people are heeding the AIDS
message. Perhaps many simply don't like or want to believe what they hear,
preferring to think that AIDS "can't happen to them." Experts repeatedly
remind us that infective agents do not discriminate, but can infect any and
everyone. Like other communicable diseases, AIDS can strike anyone. It is not
necessarily confined to a few high-risk groups. We must all protect ourselves
from this infection and teach our children about it in time to take effective
precautions. Given the right measures, no one need get AIDS.
The pandemic continues:
Many of us have forgotten about the virulence of widespread epidemics, such
as the 1917/18 influenza pandemic which killed over 21 million people,
including 50,000 Canadians. Having been lulled into false security by modern
antibiotics and vaccines about our ability to conquer infections, the Western
world was ill prepared to cope with the advent of AIDS in 1981. (Retro-
spective studies now put the first reported U.S. case of AIDS as far back as
1968.) The arrival of a new and lethal virus caught us off guard. Research
suggests that the agent responsible for AIDS probably dates from the 1950s,
with a chance infection of humans by a modified Simian virus found in African
green monkeys. Whatever its origins, scientists surmise that the disease
spread from Africa to the Caribbean and Europe, then to the U.S. Current
estimates are that 1.5 to 2 million Americans are now probably HIV carriers,
with higher numbers in Central Africa and parts of the Caribbean.
Recapping AIDS - the facts:
AIDS is an insidious, often fatal but less contagious disease than measles,
chicken pox or hepatitis B. AIDS is thought to be caused primarily by a virus
that invades white blood cells (lymphocytes) - especially T4-lymphocytes or
T-helper cells - and certain other body cells, including the brain. In 1983
and 1984, French and U.S. researchers independently identified the virus
believed to cause AIDS as an unusual type of slow-acting retrovirus now
called "human immunodeficiency virus" or HIV. Like other viruses, HIV is
basically a tiny package of genes. But being a retrovirus, it has the rare
capacity to copy and insert its genes right into a human cell's own chromo-
somes (DNA). Once inside a human host cell the retrovirus uses its own
enzyme, reverse transcriptase, to copy its genetic code into a DNA molecule
which is then incorporated into the host's DNA. The virus becomes an integral
part of the person's body, and is subject to control mechanisms by which it
can be switched "on" or "off". But the viral DNA may sit hidden and inactive
within human cells for years, until some trigger stimulates it to replicate.
Thus HIV may not produce illness until its genes are "turned on" five, ten,
fifteen or perhaps more years after the initial infection.
During the latent period, HIV carriers who harbour the virus without any
sign of illness can unknowingly infect others. On average, the dormant virus
seems to be triggered into action three to six years after first invading
human cells. When switched on, viral replication may speed along, producing
new viruses that destroy fresh lymphocytes. As viral replication spreads, the
lymphocyte destruction virtually sabotages the entire immune system. In
essence, HIV viruses do not kill people, they merely render the immune system
defenceless against other "opportunistic: infections, e.g. yeast invasions,
toxoplasmosis, cytomegalovirus and Epstein Barr infections, massive herpes
infections, special forms of pneumonia (Pneumocystis carinii - the killer in
half of all AIDS patients), and otherwise rare malignant tumours (such as
Cofactors may play a crucial contributory role:
What prompts the dormant viral genes suddenly to burst into action and
start destroying the immune system is one os the central unsolved challenges
about AIDS. Some scientists speculate that HIV replication may be set off by
cofactors or transactivators that stimulate or disturb the immune system.
Such triggers may be genetically determined proteins in someone's system, or
foreign substances from other infecting organisms - such as syphilis,
chlamydia, gonorrhea, HTLV-1 (leukemia), herpes, or CMV (cytomegalovirus) -
which somehow awaken the HIV virus. The assumption is that once HIV
replication gets going, the lymphocyte destruction cripples the entire immune
system. Recent British research suggest that some people
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