HIV
targets the immune system,
the very system which
would normally defend
the body against infections.
The virus attacks a particular
type of white blood cells
called CD4+ cells. It
hijacks the cell, inserts
its own genes into the
cell's DNA and uses it
to manufacture more virus
particles. These go on
to infect other cells.
The CD4+ host cells eventually
die, although scientists
do not know exactly how.
The body's ability to
fight diseases decreases
as the number of CD4+
cells drops, until it
reaches a critical point
at which the patient is
said to have Aids - Acquired
Immune Deficiency Syndrome.
HIV is a particular kind
of virus – a retrovirus.
While simpler than ordinary
viruses, retroviruses
tend to be harder to defeat.
They embed their genes
into the DNA of the cells
they target, so that any
new cells that the host
cell produces also contain
the virus genes.
Retroviruses also copy
their genes into the target
cell with a high level
of error. In combination
with HIV's high replication
rate, this means the virus
mutates at speed as it
spreads.
Furthermore, the "envelope"
the HIV virus particle
is contained inside is
made of the same material
as some human cells, making
it difficult for the immune
system to distinguish
between virus particles
and healthy cells.
Infection...
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