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HIV Virus

HIV (human immunodeficiency virus) is a virus that attacks the immune system, the body's natural defense system. Without a strong immune system, the body has problems to fight the disease.

 

Both the virus and the infection it causes are called HIV. HIV infects and destroys certain white blood cells called CD4 + cells. If too many CD4 + cells are destroyed, the body can no longer defend itself against the infection.

 

The last stage of HIV infection is AIDS (acquired immunodeficiency syndrome). People with AIDS have a low number of CD4 + cells and contract infections or cancers that rarely occur in healthy people. These can be fatal, and they are called opportunistic infections.

HIV is a retrovirus, that is, it uses a reverse transcriptase to transcribe its RNA genome to DNA and integrate it into the host's genome. Its taxonomic classification is:

 

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  • Kingdom: Virus

  • Family: Retroviridae

  • Genus: Lentivirus

  • Species: HIV

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The virus is approximately spherical with a diameter of about 120 nm, about 60 times smaller than a red blood cell. Its genome is made up of two copies of positive single-stranded RNA, protected by the p7 proteins that form the nucleocapsid. The single-stranded RNA is tightly bound to the and enzymes needed for the development of the virion such as reverse transcriptase (DNA-polymerase type enzyme), proteases, ribonuclease and integrase. 

 

The genome and the nucleocapsid are enclosed in a trunk-shaped capsid, which in turn is surrounded by a lipid bilayer, taken from the plasma membrane of the host cell, and equipped with certain proteins, in particular 3 gp41 molecules that form a kind of stem; and an external head formed by the gp120 glycoprotein, essential in the coupling to the CD4 receptor of T lymphocytes.

We found two types of HIV that differ according to whether they present the vpu or vpx gene. HIV-1 has the vpu gene, and the HIV-2 vpx gene. The virus contains 9 genes. Three of them codify for structural proteins common to all retroviruses (gens gag, pol and env).

 

  • Gag: codifies for the antigen of the specific group and the structural proteins.

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  • Pol: codifies for viral enzymes, which are reverse transcriptase, integrase, protease and RNAase (ribonuclease).

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  • Env: codifies for the viral envelope, and the external structural proteins that are responsible for the specified cellular type.

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The remaining six are non-structural genes, which are encoded by two regulatory proteins (genes T and T) and four accessory proteins (genes vpr, vif, nef and vpu or vpx).

HIV type 1 and HIV type 2 are two different viruses. Globally, the predominant virus is HIV-1, and generally speaking of HIV without specifying the type of virus, it refers to HIV-1.

HIV-2 is relatively unusual and concentrated in western Africa, but it has been seen in other countries. It is less infectious and progresses slower than HIV-1.

 

     -Groups within HIV-1:

 

The strains of HIV-1 can be classified into 4 groups. The most important group, M, is the "major" group and is responsible for most of the global HIV epidemic.

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The other three groups are N, O and P. They are very rare and occur only in Cameroon, Gabon and Equatorial Guinea.

 

     -Strains within group M:

 

Within group M, at least 9 genetically different subtypes of HIV-1 are known. These are the strains A, B, C, D, E, F, G, H and J. In addition, different subtypes can combine genetic material to form a hybrid virus, known as a "circulating recombinant form" (CRF), of which a few have been identified.

Global distribution of HIV-1

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