HIV originated around 1900, study shows

Tuscon, October 3: A recently held study, published in the journal Nature on Wednesday, revealed that HIVdefine- virus causing AIDS, appears to have evolved around a century ago. The researchers concluded this finding by conducting genetic analysis of a biopsy sample that was recently discovered in the Democratic Republic of Congo.

The study led by evolutionary biologist Michael Worobey of the University of Arizona in Tucson, was based on mutation rates of different subtypes of the virus. For this, researchers adopted a genetic technique in which they first determined the different subtypes' mutation rates. Having known the rate of mutation, they then went backwards to find out the exact point where subtypes were found to be the same. That common ancestor would represent the first appearance of the virus in humans before it mutated.

"The HIVdefine virus evolves incredibly quickly," said geneticist Bette Korber of Los Alamos National Laboratory in New Mexico, who did an analysis in 2000. "Those mutations get passed on to the next individual. So we have that evolutionary pace to enable a look backward."

Presently, around 33 million people worldwide are estimated to have been infected by HIV. In US, the first case of HIV was recorded in 1981, and the oldest evidence of the virus was in the form of blood sample of a Belgian Congo male resident. However, the most common form of the virus named HIV-1, is known to have originated in chimpanzees because of the close genetic similarities to a simian virus.

The researchers compared the Lymph node tissue of a Belgian Congo female who died in 1960 with modern strains to determine its mutation rate. Then they matched that rate with the 1959 sample, tracing their common ancestor to between 1884 and 1924.

"I've been trying to track down old samples like this for quite a few years now," Worobey said. "As soon as you have that one other sequence from that same time period, it really snaps the whole evolutionary picture into sharp focus."

The researchers surmised that the creation of colonial cities around the turn of the century was the catalyst that allowed the virus to take hold.

Dr. Steven M. Wolinsky, a co-author of the study, said that colonial cities meant not just more potential hosts for viruses living in closer quarters, but also prostitution and other high-risk behaviors for transmitting the virus.
"Urbanization was probably the main trigger," said Wolinsky, an infectious diseases specialist at the Feinberg School of Medicine at Northwestern University in Chicago.

Nevertheless, putting the date of origin at around 1900, this new analysis claims the evolution to be 30 years earlier than previous analyses. Korber's analysis compared the 1959 blood sample and modern samples. She had traced their common ancestor to roughly 1931.