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.
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