[afro-nets] Nature: HIV jumped to humans earlier than once thought

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HIV jumped to humans earlier than once thought

The virus is believed to have been contracted from chimpanzees between 1884
and 1924, a new genetic analysis shows

Article Comments (49)

MALCOLM RITTER
Associated Press
October 2, 2008 at 5:07 AM EDT

NEW YORK — The AIDS virus has been circulating among people for about 100
years, decades longer than scientists had thought, a new study suggests.

Genetic analysis pushes the estimated origin of HIV back to between 1884 and
1924, with a more focused estimate at 1908.

Previously, scientists had estimated the origin at about 1930. AIDS was not
recognized formally until 1981 when it got the attention of public-health
officials in the United States.

The new result is "not a monumental shift, but it means the virus was
circulating under our radar even longer than we knew," says Michael Worobey
of the University of Arizona, an author of the new work.

The results are published today in the journal Nature. Researchers noted
that the newly calculated dates fall during the rise of cities in Africa,
and they suggested urban development may have promoted HIV's initial
establishment and early spread.

Scientists say the human immunodeficiency virus descended from a chimpanzee
virus that jumped to humans in Africa, probably when people butchered
chimps. Many individuals were probably infected that way, but so few other
people caught the virus that it failed to get a lasting foothold,
researchers say.

But the growth of African cities may have changed that by putting lots of
people close together and promoting prostitution, Dr. Worobey suggested.
"Cities are kind of ideal for a virus like HIV," providing more chances for
infected people to pass the virus to others, he said.

Perhaps a person infected with the AIDS virus in a rural area went to what
is now Kinshasa, Congo, "and now you've got the spark arriving in the
tinderbox."

Key to the new work was the discovery of an HIV sample that had been taken
from a woman in Kinshasa in 1960. It was only the second such sample to be
found from before 1976; the other was from 1959, also from Kinshasa.

Researchers took advantage of the fact that HIV mutates rapidly, so two
strains from a common ancestor quickly become less and less alike in their
genetic material over time. That allows scientists to "run the clock
backward" by calculating how long it would take for various strains to
become as different as they are observed to be. That would indicate when
they both sprang from their most recent common ancestor.

The new work used genetic data from the two old HIV samples plus more than
100 modern samples to create a family tree going back to these samples' last
common ancestor. Researchers got various answers under various approaches
for when that ancestor virus appeared, but the 1884-to-1924 bracket is
probably the most reliable, Dr. Worobey said.

The new work is "clearly an improvement" over the previous estimate of
around 1930, said Anthony Fauci, director of the National Institute of
Allergy and Infectious Diseases in Bethesda, Md. His institute helped pay
for the work.

Dr. Fauci described the advance as "a fine-tuning."

Experts said it was no surprise that HIV circulated in humans for about 70
years before being recognized. An infection usually takes years to produce
obvious symptoms, a lag that can mask the role of the virus, and it would
have infected relatively few Africans early in its spread, they said.

Article available for payment at:
http://www.nature.com/nature/journal/v455/n7213/full/455605a.html

This piece of news is an interesting scientific analysis--but I am wondering how it explains the discovery of AIDS in homosexual communities in the US, years before it was ever noticed among other population groups in Europe and Asia (assuming Africa, including South Africa, has always had HIV/AIDS which went unnoticed).

Can I get an answer from HIV experts?

Atsu Seake-Kwawu

--
Dr Atsu G Seake-Kwawu
Municipal Director of Health Services,
Ghana Health Service
P.O. Box KW 198
Keta, Ghana
Tel: +233-966-42564
     +233-244-838974
     +233-243-647132
Fax: +233-966-42286
mailto:atsu@doctor.com