Aids is a serious health problem that threatens the entire
human population. It is a fast spreading incurable disease. Aids is caused by
the human immunodeficiency virus (HIV). It is a disorder of a cell mediated
immune system of the body. The AIDS virus selectively invades helper T cells
destroying or incapacitating the cells that normally orchestrate much of the
immune responses. There is a reduction in the number of helper-T cells which
stimulate antibody production by B cells. This result in the loss of natural
defence against viral infection.
HISTORY:
Aids was first described in 1981 when the centres for
Disease Control in Atlanta began to notice a disturbing similarity between
cases involving a strange collection of symptoms. It is now believed that HIV
first infected humans in the 1960s in Africa after “jumping species” from other
primates to humans.
The virus was discovered in 1984 by American scientist Robert
Gallo and French scientist Luc Montagnier independently.
AIDS may have passed from a monkey host into human population
in Africa during the 1960s. It is heartening to know that only 10% of the
people, who gets HIV virus infection actually develop full blown AIDS.
The worldwide damage done by HIV so far is truly astonishing.
Today more than 34 million people are living with HIV infection or AIDS,
representing nearly 1% of the adult population worldwide. So far, nearly 30
million people have died of AIDS, and approximately 7,400 people are newly
diagnosed with HIV every day.
STRUCTURE OF HIV VIRUS:
HIV Is 100 -140/90-120 nm in diameter, has a cylindrical core,
single stranded linear RNA and reverse transcriptase enzyme surrounded by a
glycoprotein coat, double lipid membrane and two protein coats.
The genome of HIV consists of two single stranded RNA
filaments and associated with a reverse transcriptase (P51 and p64),
Integrase (p32), and Protease (p10) enzymes and some
minor proteins and the major core protein molecule.
The virus’s genetic material is protected by a series of
three protein coat: the nucleocapsid, capsid and matrix. Within the matrix are
the following three very important enzymes
i. reverse transcriptase(P51,,P64): It
catalyses reverse transcription, the conversion of the viral RNA to viral DNA.
ii. integrase (P32): It catalyses the integration
of viral DNA into the DNA of the host cell.
iii. protease (P10): It catalyses the breakdown of
the newly synthesised viral polypeptides into functional viral proteins.
The genome of HIV is a millionth the size of ours, and its
nine genes, consisting of about 9000 RNA bases encode only 15 proteins. But HIV
affects more than 200 human proteins as it invades the immune system.
The single stranded RNA of HIV enclosed by conical capsid
composed of the viral proteins P24; typical of lentiviruses.
The single strand RNA is
tightly bound to P7 nucleocapsid proteins, late assembly protein P6, and
enzymes essential to the development of the virion, Such as reverse
transcriptase and integrase. The nucleocapsid associates with the Genomic RNA
and protect the RNA from digestion by nuclease.
The envelope of the virion is
formed by a plasma membrane of host cell origin, which is supported by a matrix
composed of the viral P17 protein, ensuring the integrity of the viral in
particle.
At the surface of the virion
can be found a limited number of the envelope glycoprotein of HIV, a trimmer
formed by heterodimers of GP 120 and GP41. Envelope glycoprotein is responsible
for binding to its primary host receptor CD4 and its co-receptor mainly CCR5 or
CXCR4, leading to viral entry into its target cell.
To be Continued………
