Human immunodeficiency virus (HIV virus) is a virus of the lentivirus family i.e. it can deliver more information into the DNA of the host cell. Its characteristic properties are that it is the one which leads to long-duration illnesses accompanied by a long incubation period. Also the HIV virus is said to be responsible for causing one of the most dreaded disease “AIDS” in the human body. AIDS is known to affect the immune system of the body by opportunistic infections.

Origin:
HIV virus is believed to be originated from the non-human primates of the sub-Saharan Africa and then transferred to the humans during the early 20th century. When the virus once infects the system then in that case there can be two possibilities:
1. The virus becomes latent and the infected cell continues to function as usual.
2. The virus becomes active inside the body and replication continues, thus infecting a large number of cells of the immune system inside the body.

Classification of HIV virus:
It has been observed that two species of HIV exist:

• HIV-1
• HIV-2.

The comparison between the two can be made on the basis of many factors like Transmittability, existence, virulence etc. as follows:

Properties	HIV-1	HIV-2
Existence	Global	West Africa
Transmittability	High	Low
Virulence	High	Low
Origin	Chimpanzee	Sooty mangabey

Mode of Transmission:
This virus is transmitted in our body with the transfer of bodily fluids like blood, semen, vaginal fluids or breast milk i.e., whenever there is a transfer of bodily fluids from an HIV infected person to a normal person then the virus is transmitted to the receiver.

Effects of HIV virus:
The HIV virus is known to affect the immune system cells of our body and cause flu like illness. It affects the helper Tcells, macrophages, and dendritic cells. After continuous reduction seen in the CD4+ T cells, the cells tend to loose their cell-mediated immunity thus making the body prone to other opportunistic infections.

Structure of the virus:
The HIV virus is spherical in shape with a diameter of about 120 nm. It consists of two copies of positive single-stranded RNA which is responsible for coding the genes for the virus enclosed in a conical capsid consisting of copies of the viral protein. The single stranded RNA is tightly bound to the nucleocapsid proteins and other enzymes. This capsule is surrounded by a viral envelope composed of two fatty molecule layers. Inside the viral envelope are embedded the proteins from the host cell. The three molecules called the glycoprotein are responsible for anchoring the structure inside the envelope.

Replication/reproduction of HIV virus:
Following are the steps involved in the replication of the virus:

1. Entry to the cell
HIV enters the immune system’s macrophages and CD4+ T cells by the process of adsorption of glycoproteins on their surface to the receptors on the target cell following fusion of the viral envelope with the cell membrane and thereafter releasing the HIV capsid into the cell.

2. Replication and transcription
After the entry of the viral capsid into the cell, an enzyme called reverse transcriptase holds the responsibility of liberating the single-stranded RNA from the attached viral proteins and copying them into complementary DNA. The reverse transcriptase further responsible for the formation of a complementary DNA strand forming a double-stranded vDNA.

3. Assembly and release
The final step is the assembly of the new HIV-1 virus species, which tends to start at the plasma membrane of the host cell.

Treatment:
Although HIV is one of the dreaded viruses affecting the human body but it can be treated using recent medications and drugs. Also, being infected with the HIV is not a thing to worry about as drugs and various other medications are available to keep a check on the virus.