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
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,