How HIV works and can be detects
human body responds to infection and disease through the action of cells in the
blood called white blood cells. These cells recognise invaders and produce
antibodies, which are chemicals that attack and neutralise the invaders.
specific antibody is produced for each disease, with most disease, once a person
has developed antibodies against it, the cells responsible remember how to
produce that antibody-and the person is immune to that disease for the rest of
antibodies which the body produces in response to HIV, and which can be detected
in the blood of an HIV carrier, do not seem to be effective in preventing the
spread of the virus in most people.
attacks and inactivates a particular kind of white blood cell, known as a T4
helper cell. T4 helper cells are vital in controlling the body’s defence to
many diseases. They also recognise disease to many diseases. They also recognise
disease organisms and cancer cells which the white blood cells must destroy
after an infection. The T4 helper cells stimulate the production of a large army
of white blood cells to fight the infection. Sometimes they are successful in
this. Sometimes the infection or cancer is so over whelming, or grows so
rapidly, or is composed of cells immune to the T4 cells, that the illness wins.
Sometimes, the body itself suffers from a weakness of the cells that provide
immunity, such as the T4 cells, and do the disease overwhelms the body. This
partly explains why people can die of any illness.
ability to the T4 cells to counter some of the many disease to which the body is
the body remain able to counter many other diseases and cancers. This is why it
is possible to go an living for so long even if a person has AIDS. The few
diseases that do occur in such people can be treated. As more and more T4 cells
are destroyed, the efficacy of this treatment is reduced, and so treatment
becomes harder to maintain.
tests that are used most widely merely detect the presence of some of the anti
bodies produced by the body in the response to the presence of the virus.
commonest of these tests is the ELISA test (Enzyme-Linked Immuno Sorbert Assay).
The costs vary, but the cheapest ELISA test cost in the region of US$0.75 per
test, and the cheapest western Blot test ( used for confirmation of a positive
ELISA test) cost about US$9. In addition there is a cost training of
specialised staff, provision
of laboratory equipment and maintenance.
although most people who are infected with HIV produce antibodies, the period
before antibodies appear varies considerably. Most seem to produce antibodies
within three months of infection but some may only begin to produce antibodies
three years after infection, and some may never produce antibodies at all. The
response seems to depend on the route of infection, the dose of the virus, the
response of the infected person, and the frequency of exposure to the virus. In
blood – borne infections the usual period before antibodies appear is about
6-8 weeks. It may be that in those who have had a minimal exposure, the virus
takes a long time to multiply to the level at which it stimulates an antibody
response. There is at present no other widely available method other than the
woman antibody test – of saying definitely whether or not a person is infected
– unless they go on to develop the illness associated with aids.
further problem is that the tests used in a very few cause say no antibody
present when they are (false negatives), or, more commonly, say antibodies are
present when they are not (false positives).
tests, whilst useful for certain situations such as the screening of blood
donation, are quite limited in some other situations.