Acquired immunodeficiency syndrome:AIDS:Biochemistry:U.Satyanarayana

A cquired immunodeficiency syndrome (AIDS)
Awas first reported in 1981 in'homosexual
men. AIDS is a retroviral disease caused by
human immunodeficiency virus (HlV). The
disease is characterized by immunosuppression,
secondary neoplasma and neurological
manifestations. AIDS is invariably fatal since
there is no cure. In the USA, it is the fourth
leading cause of death in men between the ages
15 to 55 years.
No other disease has attracted as much
aftention as AIDS by the governments, public and
scientists. AIDS has stimulated an unprecedented
amount of biomedical research which led to a
major understanding ofthis deadfy disease within
a short period of time. So rapid is the research on
AIDS (particularly relating to molecular biofogy),
any review is destined to be out of date by the
time it is published!
The isolation of human immunodeficiency
virus (HIV) from lymphocytes of AIDS patients
was independently achieved by Gallo (USA) and
Montagnier (France) in 1984.
Epidemiology
AIDS was first described in USA and this
country has the majority of reported cases. The
prevalence of AIDS has been reported from
almost every country. The number of people
living with HfV worldwide is estimated to be
around 40 million by the end of the year 2005.
(lndia alone has about 5 million persons). At
least 5 million deaths occurred in 2005, due to
AIDS. AIDS is truely a global disease with an
alarming increase in almost every country.
Transmission of HIV : Transmission of AIDS
essentially requires the exchange of body fluids
(semen, vaginal secretions, blood, milk)
containing the virus or virus-infected celfs. There
are three major routes of HIV transmission-
sexual contact, parenteral inoculation, and from
infected mothers to their newborns.
The distribution of risk factors for AIDS trans-
mission are as follows.
Sex between men (homosexuals)
Sex between men and women
- 60"/"
-15%Intravenous drug abusers - 15"/"
Transfusion of blood and blood products - 6%
All others - 4o/o
The predominant methods of HIV
transmission (about 75o/") are through anal or
vaginal intercourse. The risk for the transmission
is much higher with anal than with vaginal
intercourse. The practice of 'needle sharing' is
mainly responsible for the transmission of HIV in
drug abusers. Pediatric AIDS is mostly caused by
vertical transmission (mother to infant).
It should, however, be noted that HIV cannot
be transmitted by casual personal contact in the
household or work place. Further, the
transmission of AIDS from an infected individual
to health personnel attending on him is
extremelv rAre.
Virology of HIV
AIDS is caused by a retrovirus, namely human
immunodeficiency virus (HlY), belonging to
lentivirus family. Retroviruses contain RNA as
the genetic material. On entry into the host cell,
they transcribe DNA which is a complementary
copy of RNA. The DNA, in turn is used, as a
template to produce new viral RNA copies.
Two different forms of HlV, namely HIV-I
and HIV-2 have been isolated from AIDS
patients. HIV-1 is more common, being found in
AIDS patients of USA, Canada, Europe and
Central Africa while HIV-2 is mainly found in
West Africa. Both the viruses are almost similar
except they differ in certain immunological
properties.
HIV-1 is described in some detail.
Structure of HIV : The viruse is spherical with
a diameter of about 110 nm. lt contains a core,
surrounded by a lipid envelop derived from the
host pfasma membrane (Fig.3fl.l). The core of
the HIV has two strands of genomic RNA and
four core proteins, PZq, PtB, reverse tranScriptase
(poolpsr) and endonuclease (p32). Note that the
naming of the proteins is based on the molecular
weight. For instance, a protein with a molecular
weight of 24,0OO is designated as p2,4.
The lipid membrane of the virus is studded
with two glycoproteins Bprzo and gpot. The
surface antigen 8p126 is very important for the
viral infection CD4.