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The AIDS virus, to put it simply, consists of genetic information on
the inside and a protective outer shell of proteins and glycoproteins.
Since viruses use the host cell's resources for reproduction, they don't
need to contribute much themselves. That's why they are much smaller
than the host cells, e.g. helper T cells. In the host cell's nucleus,
displayed in blue here, there are more than 100,000 times as much genetic
information stored than under the protein shell of the AIDS virus. However,
there is no way for the host cell to stop the virus once the cell has
been infected.
The infection proceeds in this manner: The virus anchors itself to a
special protein (CD4) on the surface of the helper T cell. This causes
the viral membrane to fuse with the host cell's membrane. This way the
genetic information gets inside the cell.
The AIDS virus belongs to a special group of viruses. Its genetic information
is not encoded as DNA, but instead as RNA (ribonucleic acid) and therefore
has to be reverse transcripted into DNA. The tools for this are delivered
by the host cell itself, except for a little helper protein (reverse
transcriptase) which the virus has brought with itself. The DNA is now
legible for the cell and is transferred to the nucleus. This process
is already finished by a half of a day after infection. The foreign
piece of DNA is then inserted randomly into the host DNA and it is now
ready to be transcribed.
At the beginning of AIDS, the viral DNA is being transcribed to form
many RNA molecules--the signal which causes this is yet unknown. The
accruing RNA is carried to the cytoplasm of the cell, where it can start
making proteins.
The RNA, with the help of the host's resources, begins to make many
copies of the different parts of the AIDS virus (the protective shell
and the helper and anchor proteins).
After everything has been copied, thousands of bubbles like these are
produced and migrate to the cell membrane surface and fuse with it.
Finally, a copy of the RNA genetic information is added to the bubble.
Then this section of the cell membrane turns inside out and new viruses
leave the cell.
Naturally, the release of the new AIDS viruses significantly weakens
the host cell which soon dies.
That is how the immune system weakens and AIDS starts.
In early 1996 there were 28m people infected worldwide. This number
includes people who already died of AIDS.
Diagnosis
HIV infection is diagnosed on the basis of blood tests using three different ELISA/Rapid simple tests using different antigen preparation.
AIDS cases are diagnosed on the basis of two different ELISA/Rapid tests on different antigens and presence of AIDS related opportunistic infections.
Western Blot test is used for confirmation of diagnosis of indeterminate ELISA tests.
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