By Amy Norton
NEW
YORK (Reuters Health) - A controversial theory that the world's HIV epidemic arose
from an oral polio vaccine used in Africa in the 1950s has no scientific evidence
to back it up, according to four separate studies released Thursday.
The
studies, from researchers in the US, UK, France and Germany, should help free
the polio vaccine manufactured by the Wistar Institute in Philadelphia, Pennsylvania,
from lingering questions over its proposed role in creating the HIV scourge.
Proponents
of the oral polio vaccine (OPV) theory have suggested the Wistar vaccine used
in a 1950s anti-polio campaign in Africa was cultured in chimpanzee kidney cells.
These chimp cells, they say, may have been contaminated with the virus that became
HIV-1, the strain responsible for most of the world's HIV infections. The Wistar
Institute has always denied that any chimp cells were used in manufacturing its
OPV.
But the fact that mainstream researchers believe HIV arose from the
related simian immunodeficiency virus (SIV) in chimps has bolstered the idea that
HIV was mistakenly unleashed through polio vaccination. The theory was first made
famous in a 1992 Rolling Stone article, and the idea gained more steam with the
1999 publication of journalist Edward Hooper's book "The River."
But in
new findings published in the journals Nature and Science, four research teams
demonstrate that the Wistar vaccine did not contain chimp cells and that the virus
that would become HIV likely jumped from chimps to humans just once--and not through
a massive, simultaneous transfer, as it would if vaccination were to blame.
"I
am not sure what the OPV theory people will say, but as far as I am concerned
the theory is dead," Dr. Edward C. Holmes of the University of Oxford, UK, told
Reuters Health. "There is not one piece of hard evidence supporting it."
Holmes
led a team that traced the roots of HIV-1 through a genetic analysis of blood
samples from HIV-infected people in the Congo, which was ground zero for the Wistar-vaccine
campaign of the 1950s. They compared the results with genetic analyses of all
the world's known HIV strains.
The investigators found, contrary to the
OPV theory, that HIV strains in the Congo do not appear to have appeared all at
once. Moreover, they report, the study supports the belief that the HIV virus
common to today's strains was present in a human, long before the polio vaccination
campaign in Africa.
The three other studies analyzed frozen samples of
the Wistar vaccine in question. In each, scientists found no evidence of chimpanzee
genetic material or SIV in the vaccine samples. Instead, the studies confirmed
that the vaccines were made with cultured cells from macaque monkeys, which do
not harbor SIV.
There was "never any evidence" the Wistar vaccine contained
chimp cells, let alone SIV-infected cells, Dr. Claudio Basilico, a co-author on
one of the studies, told Reuters Health.
"It's almost impossible to disprove
a theory," said Basilico, of New York University School of Medicine in New York
City. "But," he added, "I hope this puts the whole thing to rest."
Echoing
that sentiment, an editorial published in Nature pronounces the polio vaccine
"not guilty" of starting the HIV epidemic.
"These new reports dismiss what
reasonable conjecture existed," writes Robin A. Weiss of University College London
in the UK.
For example, one of the central arguments made by OPV theorists
is that a number of HIV strains appeared in humans at roughly the same time, in
a "starburst" fashion. They claim this as evidence the virus diversified into
various strains while still in chimps, and that all the strains were transferred
to humans at once through vaccination.
But the new genetic evidence from
Holmes' study suggests otherwise, Weiss points out.
Holmes told Reuters
Health the genetic analysis provides no evidence that a number of HIV strains
cropped up simultaneously in the Congo. "To put it another way," he said, "there
was no starburst."
Instead, he suggested, the apparent sudden rise of multiple
HIV strains is more likely due to scientists' lack of virus samples from the Congo
before the late 1950s. His team believes a larger-than-suspected number of HIV
strains dwelled within humans well before the polio vaccination campaign.
According
to Weiss, the current evidence bolsters the idea there was a "patient zero" from
whom all HIV strains eventually evolved. The spread of HIV throughout the world,
Weiss writes, could have begun with the use of non-sterile needles in Africa during
the mid-1900s.
SOURCE: Nature 2001;410:1035-1036, 1045-1048; Science 2001;292:743-744. |
