HIV and Visna

Brian Foley btf at
Thu Nov 4 11:49:10 EST 1999

"Sharon Myers" <spm at> wrote:

> Thank you, Jorge. May I ask, please, what do you think is 
> the most plausible explanation for the origin of AIDS based 
> on the information currently available? 

	There are two major viruses that cause AIDS, HIV-1
and HIV-2.  Within these two major lineages of himan 
immunodeficiency virus there are subgroups which most likely
represent independent simian to human transmission events.
For HIV-1 there are 3 independent chimpanzee to human 
transfers to create the HIV-1 M, N and O groups.  It is possible
that the subtypes within the HIV-1 M group also represent 
independent chimpanzee to human transfers, or the M group
could have diversified into subtypes within humans.  For
HIV-2 there have been at least 6 sooty mangabey to human 
transfers to create six known lineages of HIV-2. 

> Is it true that the AIDS virus is similar to visna?

	Visna virus is a lentivirus, and both HIV-1 and
HIV-2 are lentiviruses.  Visna, Bovine immunodeficiency virus,
feline immunodeficiency virus, equine infectious anemia virus, 
Jembrna disease virus, and other non-primate lentiviruses
are all approximately equidistant from the primate 
immunodeficiency virus lineage.  Within the primate 
immunodeficiency virus lineage, it is very clear that HIV-1
is most closely related to SIV from chimpanzees (especially
the Pan troglodytes troglodytes subspecies, the SIV from
Pan troglodytes schweinfurthii is a bit more distantly related).
Likewise HIV-2 is very closely related to SIV from sooty

> If the technical cites do exist, and if you have read 
> them, can you explain, from your understanding, what a 
> correct interpretation would be? 

	HIV-1 somehow crossed from chimpanzees into humans,
most likely 3 different times, but possibly as many as
14 or more times.  There are several viable theories about how
these transfers happened.  One is that humans killing and 
butchering chimpanzees for food got blood-blood contamination
through knife cutes.  Another is that humans capturing chimpanzees
to sell as pets, zoo animals, research animals, etc. got
scratched or bitten by live chimps in the process.  A third
is that a lot of polio vaccine could have been produced by using
chimpanzee kidney cells (contaminated with chimpanzee CD4 cells
and/or macrophages) and given as a live oral vaccine (OPV) to
humans in Africa or other parts of the world.  The dates that
these transfers took place are uncertain, except for the OPV
theory for which dates of vaccinations have been kept in records.
It is clear that the origin of the HIV-1 M group was some time
before 1930, but it remains possible that this origin was in
chimpanzees, and that there were many chimp to human transfers
of various subtypes some time after 1930.
	Likewise with HIV-2 there have been several sooty
mangabey to human transfers, and the exact mechanisms and
dates have not been proven yet.  In areas of Africa where
sooty mangabeys are kept as pets, local humans infected with
HIV-2 which is very closely related to the local strain of
SIV found in sooty mangabeys have been found.  For a report, 

Chen Z, et al. 
    Genetic characterization of new West African simian 
    immunodeficiency virus SIVsm: geographic
    clustering of household-derived SIV strains with human 
    immunodeficiency virus type 2 subtypes and
    genetically diverse viruses from a single feral sooty 
    mangabey troop. 
    J Virol. 1996 Jun;70(6):3617-27. 
    PMID: 8648696; UI: 96211494. 

> I am not a scientist but I can usually follow fairly technical
> details and would appreciate understanding why AIDS could 
> _not_ be an engineered virus.

	AIDS is not a virus, it is an aquired immunodeficiency
syndrome caused by depletion of CD4 cells by any one of
several types or subtypes of human immunodeficiency viruses.
So far, only HIV-1 and HIV-2 have been discovered, but it
is likely that other simian immunodeficiency viruses such
as those carried by subspecies of African green monkeys, could
also infect humans.  There is no way to absolutely prove that
HIV-1 or HIV-2 were not grown in a lab, but all the available 
evidence indicates that the epidemic was already underway in
the late 1950s and that it is most likley that at least some
of the many simian to human transfer events took place prior
to 1930.  
	Two solid cases are the 1959 serum from the Congo (formerly
Zaire) found to contain an HIV-1 infection that is ancestral to the
modern HIV-1 subtypes B and D, and the Norwegian sailor and his
family who died of AIDS in the 1960s and who were infected with 
an ancestor of HIV-1 group O.  See:

 Zhu T, et al. 
    An African HIV-1 sequence from 1959 and implications 
    for the origin of the epidemic. 
    Nature. 1998 Feb 5;391(6667):594-7. 
    PMID: 9468138; UI: 98127656.

Wain-Hobson S. 
    Immunodeficiency viruses. 1959 and all that. 
    Nature. 1998 Feb 5;391(6667):531-2.
    PMID: 9468129; UI: 98127647.

Jonassen TO, et al. 
    Sequence analysis of HIV-1 group O from Norwegian 
    patients infected in the 1960s. 
    Virology. 1997 Apr 28;231(1):43-7. 
    PMID: 9143301; UI: 97288323.

	Another case, from a sailor from Manchester England
who died of immune deficiency in 1959 could not be proven to 
be due to any viral infection.

	The technology for working with lentiviruses, which
require very specific conditions for growth and study, was not
yet developed in the 1950s.

|Brian T. Foley               btf at                 |
|HIV Database                 (505) 665-1970                   |
|Los Alamos National Lab         |
|Los Alamos, NM 87544  U.S.A.                                  |

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