CHICAGO (AP) -- Scientists have pinpointed what is believed to be
the earliest known case of AIDS -- an African man who died in 1959 --
and say the discovery suggests the virus first infected people in
the 1940s or early '50s.
Where AIDS came from is still a mystery, although experts assume
an ancestor of the virus crossed from monkeys or other primates
into people at some point. However, whether this occurred in recent
decades or centuries ago is a matter of debate.
Now, researchers say they have conducted genetic analysis of an
HIV sample that appears to date from early in the epidemic. They
believe it is an ancestor of the viruses that have infected more
than 40 million people worldwide, most of them since the early
1980s.
Dr. Toufu Zhu of the University of Washington in Seattle
presented the findings Tuesday at the Fifth Conference on
Retroviruses and Opportunistic Infections. They will also be
published this week in the journal Nature.
``This is to date the oldest known HIV case,'' said Dr. David
Ho, head of the Aaron Diamond AIDS Research Center at Rockefeller
University and a co-author of the study.
Until now, the earliest, undisputed cases of AIDS were from the
late 1960s and involved members of a family in Norway, Ho said.
In the new study, scientists looked for signs of HIV in 1,213
blood samples that were gathered in Africa between 1959 and 1982.
They found clear signs of the virus in one taken from a Bantu man
who lived in Leopoldville, Belgian Congo -- what is now Kinshasa,
Congo -- in 1959.
The virus in the sample had degraded, but the scientists were
able to isolate four small fragments of two viral genes. One gene
holds instructions for assembling the outer coat of the virus,
while the other is code for one of the proteins the virus needs to
reproduce.
HIV mutates quickly. About 1 percent of its genetic material
changes each year. So the scientists compared the genes from the
39-year-old sample of HIV with those carried by current versions of
HIV.
``We realized that if we had an old sequence'' of HIV genes,
``it would serve as a yardstick to measure the evolution of the
current HIV,'' Ho said.
HIV has mutated over the years to form 10 distinct subtypes,
lettered A through J. One of these, subtype B, is the dominant
strain in the United States and Europe, while subtype D is most
common in Africa.
The family tree of HIV looks like a bush with the various
subtypes forming the limbs. Ho said the 1959 HIV is near the trunk,
around the point where subtypes B and D branch off.
``This is no doubt an ancestor to B and D,'' he said.
Zhu said this suggests that all the HIV subtypes evolved from
one introduction of HIV into people, rather than from many
crossovers from animals to humans, as some have speculated. And
given the steady rate at which HIV mutates, it also means that the
virus probably first got into people sometime in the 1940s or early
'50s.
``I would say this is the oldest, totally unambiguous look at
HIV that we have,'' said Dr. Simon Wain-Hobson of the Pasteur
Institute in Paris. He was not involved in the study.
A few years ago, British researchers reported that a Manchester
sailor, who also died in 1959, was the oldest case. However, Ho's
group provided evidence that the HIV in that man's blood was
actually contamination that entered the sample long after he died.
Dr. Anthony Fauci, head of the National Institute of Allergy and
Infectious Diseases, said the latest discovery does not help those
who have AIDS now, but having the early genetic snapshot of HIV may
allow experts to predict how the virus will evolve over the next 10
or 15 years.
The study also does not explain how AIDS spread and became an
epidemic.
However, the researchers speculated that it could have been
unwittingly transmitted in Africa through unsterilized needles used
in vaccination campaigns.
Other potential factors that could have hastened the spread
include the end of colonial rule and the introduction of
automobiles and shanty towns.
