Question

What is the difference between HIV-1 and HIV-2?

27 September 2006. Related: All topics, Other tests.

What is the difference between HIV1 and HIV2 with regards to structure, function, occurence and survival in the environment?

Answer

Answer: Simon Collins

HIV-1 and HIV-2 are two different viruses. HIV-1 is the main family of HIV and accounts for 95% of all infections worldwide. HIV-2 is mainly seen in a few West African countries. The spread in the rest of the world is negligible.

Although HIV-2 generally progresses more slowly than HIV-1, some HIV drugs (NNRTIs like nevirapine and efavirenz) do not work against HIV-2.

On a structural level HIV-1 and HIV-2 have important genetic differences. A technical description of the difference is that the vpu gene found in HIV-1 is replaced by the vpx gene in HIV-2. In addition, the protease enzymes from the two viruses, which are aspartic acid proteases and have been found to be essential for maturation of the infectious particle, share about 50% sequence identity.

There are, however, differences in substrate and inhibitor binding between these enzymes. Most notably between the CGP 53820 inhibitory binding.

On functional level, there is a difference between the two viruses in terms of how easy it is for the virus to infect someone. HIV-1 enters the immune system by attaching onto the CD4+ receptor found on the surface of certain white blood cells. HIV-2 has a harder time gaining such a foothold.

So HIV-2 generally progresses much more slowly, with lower viral laod and slower risk of becoming sick. However, some HIV drugs (including NNRTIs) are not active against HIV-2.

Both viruses are fragile and highly susceptible to physical and chemical agents and therefore do not survive well outside the human body. HIV in blood or sexual fluid for example is not infectious after it has been outside the body for a few minutes.

Notes: this answer was updated in January 2018.