HIV-1 vs HIV-2

[Patrick O'Neil]

On 15 Mar 1995, Gary Ross wrote:

> Hi.  I am a biologist but have been working out of field for   
> about seven years.  Can someone give me a brief(?) rundown on   
> HIV-1 vs HIV-2 viruses?
> 

HIV in general appears to have jumped into humans from Gabonese mandrills
from 1 to 2 centuries ago.  From this jump, the two HIV strains diverged,
with HIV-1 later jumping from humans to chimpanzees (no, sexual activity
is not implied nor necessary) leading to that particular SIV variant.  

In the HIV-2 line, a virus jumped into green monkeys, which then jumped 
into a host of other simians.

The most parsimonious scenario of all has an HIV ancestor incubating 
within human populations for about a thousand years or so, with jumps 
into various simian lines within the last few centuries.

As to the specifics of the HIVs and their infectivity, HIV-1 appears to 
have originated in the western region of central Africa and is the more 
virulent of the two main strains.  The frequency of AIDS in areas of 
Africa where HIV-2 predominates is lower than those in which HIV-1 
predominates.  Those with AIDS or AIDS-like symptoms also deteriorate 
more rapidly if they are infected with HIV-1.  In part this may be due to 
the activity of reverse transcriptase, which is faster in HIV-1 infected 
cells.  Another difference is in number of replication stimulating sites 
in the genome.  HIV-1 has two binding sites for NF-kB while HIV-2 has one 
and also requires other factors for replication activation.

Overall infectivity also appears different:  In the Ivory Coast, mothers 
infected with HIV-2 infect about 10% of their babies while those infected 
with HIV-1 infect about 50%.  It also appears that transmission per 
sexual act is 4 times more likely for HIV-1 than HIV-2.

Genetically, the two variants are essentially the same as far as 
overall genome arrangement and phenotype are concerned.  The predominant 
form of HIV infection in the US and Europe is HIV-1.

Actually, the HIVs share quite a lot with all other retroviruses, as far 
as genome and virion packaging.

I suggest: Virology, Second Edition, edited by B. N. Fields, D. M. Knipe 
et al. Raven Press, Ltd., NY 1990.  Chapter 51, Retroviridae and Their 
Replication.

M. Ricchetti. 1991. Reverse transcription and the RNA and DNA world.  
Bull. Inst. Pastuer, 89:147-158.

Evolution of Infectious Disease by Paul W. Ewald, Oxford Univ Press, NY, 
1994.

Patrick