February 4, 1999. Copyright, 1999, Graphic News. All rights reserved

AIDS: ANOTHER PIECE IN THE JIGSAW
By Duncan Mil

LONDON, February 4, Graphic News:  The incredible story of how scientists discovered that the human AIDS virus originated in Central West African chimpanzees began more than 20 years before AIDS itself was first identified, with the capture of a young female chimp and a blood sample from a dead African.
The chimpanzee, called Marilyn, was one of a group captured in Africa in 1959 and used by the U.S. Air Force for medical experiments.
In 1985, a year after HIV Ð human immunodeficiency virus Ð was discovered to be responsible for the emerging AIDS epidemic, the Air Force chimps became crucial in the search for a cure.
ÒWe were setting up to test vaccines and the animal that is most readily ÔinfectableÕ by HIV other than humans is chimpanzees,Ó says Dr. Larry Arthur of the U.S. National Cancer Institute.
While screening more than 90 chimps to test, scientists discovered that Marilyn was already infected with what appeared to be HIV Ð simian immunodeficiency virus, known specifically as SIVcpz.
ÒJust as we found she was HIV-positive, she died giving birth to twins Ð we asked them to send the organs to us so we could try to isolate the virus from it,Ó Dr. Arthur said.
Because the technology wasnÕt yet available to establish if the chimp was infected with the same virus that was infecting millions of humans, the researchers put MarilynÕs remains in a freezer and waited.
Ten years later, needing room in a now full freezer, the remains were almost thrown away. But then Dr. Arthur remembered there were researchers in Alabama studying chimps for the origin of HIV and who were using a new technique known as polymerase chain reaction (PCR).
Dr. Beatrice Hahn of the University of Alabama and colleagues used PCR to analyse blood and tissue samples from Marilyn and confirmed she was infected with SIVcpz.
Prior to the Marilyn discovery only three other cases of chimpanzees infected with SIVcpz had been documented worldwide.
Having found the virus in Marilyn, HahnÕs team compared it to samples from the other three chimps and to several strains of HIV.
In one case the virus was genetically not very close to HIV, but came from a subspecies of chimp known as Pan troglodytes schweinfurthii.
However, the three SIV strains taken from the Central West African chimps, known as Pan troglodytes troglodytes and including Marilyn, were virtually the same as the one that causes AIDS in humans.
But where does the human blood sample come into the story? Last year, researchers at New YorkÕs Rockefeller University, who analyzed the plasma sample, concluded they had found the first known case of AIDS Ð 22 years before the epidemic began in America. The sample came from a Bantu man who died in early 1959 in Leopoldville (Kinshasa), in the Belgian Congo, now the Democratic Republic of Congo Ð an area where this subspecies of chimp was known to live.
ÒThis infection in chimpanzees has probably existed for a long time,Ó says Dr. Hahn. Her colleagues believe perhaps for thousands of years before the virus was transmitted to human beings Ð likely through killing chimpanzees and eating their meat.
Even if Dr. HahnÕs discovery does not lead to a cure, it likely answers a central issue about the AIDS virus Ð where it comes from and how it was transmitted to humans.
ÒOn occasion you get lucky,Ó says Dr. Hahn.
/ENDS

Sources: Nature Magazine, World Wildlife Fund, Reuters