What is Human Immunodeficiency Virus (HIV)?

HIV is the aetiological agent of AIDS.
HIV is an enveloped virus.
Diameter is 90 - 120 nm.
It has a nucleoprotein core containing single stranded RNA genome and proteins.
Viral RNA associates with reverse transcriptase enzyme.

This enzyme is a characteristic feature of retroviruses. Therefore, HIV belongs to

RETROVIRES family

Retrovirus family is subgrouped as

Spumavirus
Oncovirus
Lentivirus

HIV belongs to lentivirus subgroup.

TWO types of lentiviruses,

a) One type is causing degenerative neural diseases in animals.
b) The other one causes immunodeficiency.

The other three types are:

(1) Human Immunodeficiency Virus (HIV)

Type 1 & 2
These two types infect humans.
Type 2 almost entierly confined to West Africa.

(2) Simian Immunodeficiency Virus (SIV)

This type causes Simian AIDS.

(3) Feline T Lymphotrophic Virus (FTLV)

This type causes Feline AIDS.

Structure

HIV contains single RNA and reverse transcriptase enzyme is attached to the RNA strand.
RNA contains viral proteins (P 9/P 7).
RNA is surrounded by a core protein (P 24/25).
Core protein is covered by a viral protein (P 17/18).
Outside the viral protein, a lipid bilayer is seen. It contains two other proteins called gp 120 and gp 41.
Protein gp 120 is anchored to protein gp 41.

Antigenic variation

HIV undergoes frequent antigenic variations both core and envelope antigens.

Two different antigenic types are seen.

HIV - 1
HIV - 2

Variations occur within HIV - 1 and 2 types.
It is likely that more HIV types may be identified.

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