New evidence dates diverse HIV strains from Africa to 1960

Urban development may have facilitated spread of the disease as early as the late 1800s.

Issue: November 2008

A strain of HIV taken from a sample obtained in 1960 in Leopoldville, Belgian Congo (now Kinshasa, Democratic Republic of the Congo) may offer insight into understanding of the virus, according a report published in Nature.

Researchers from the University of Arizona, Sanofi Pasteur and other sites discovered tissue from a biopsy conducted on a woman from the Congo in 1960. They extracted a viral sequence from the tissue, which had been preserved in paraffin wax.

The researchers called the sequence DRC60. The genetic divergence between this strain and the publicized ZR59 strain showed that HIV was diversified in West/Central Africa long before the AIDS epidemic came into view, according to the researchers.

Michael Worobey, MD, assistant professor of ecology and evolutionary biology at the University of Arizona, was one of the researchers involved in the project. “We are basically trying to use evolutionary trees of these viruses to infer when, where and how they emerged,” he told Infectious Disease News. “If you have samples that come from several time points, including the present time, you can actually see the rate at which evolution happens and then calibrate the overall rate. You can look at the root of the tree and put a time estimate on the ancestor of the whole AIDS pandemic.”

The genetic distance between ZR59 and DRC60 has led the researchers to believe that HIV not only has been flourishing for far longer than was previously thought but also that it may have jumped the species barrier much earlier as well. The genetic differences between the two strains demonstrated that HIV may have been in humans as early as the turn of the 20th century.

Worobey said that researchers create complex models to observe the basic reproductive rate of epidemics. In the end, though, it comes down to a simple mathematical equation. “If the average person who is infected with something passes it on to at least one other person, the epidemic is going to take hold and spread. If the average person passes it on to less than one person, the epidemic will go extinct,” Worobey said.

If HIV had been passing from chimpanzees into humans prior to the turn of the 20th century, it had been going extinct each time, he said. “But there must have been some changes that pushed that magic number above one, so that once it got into humans, it started this chain of infections.”

The researchers suggested that a key factor in the spread of the disease may have been the rise of cities like Kinshasa. Increased trade and interaction may have allowed transmission to occur more efficiently.

Current, future implications

Many researchers in the field have indicated that it is hard to believe that the disease has been circulating as long as it has. They believe that it could not have gone without detection for so long. The genetic differences between ZR59 and DRC60 make a strong argument against that belief. Further, Worobey also suggested that the delayed onset of symptoms and the varying causes of death induced by AIDS makes it very plausible that physicians could have missed it entirely.

However, Worobey said this can positively help clinicians in the present and future. “At a basic level, being able to see a clear, long view of the genetic development of HIV may help us predict where it is going,” he said. Also, he said that with vigilance, it may be possible to notice and react to the next such virus earlier.

Worobey cited ways in which research like his can be applied to practical purposes. He said that researchers are considering using ancestral HIV gene sequences as a starting point for vaccines. “It may be a long shot, but the research we have conducted so far certainly has furthered the understanding of the evolution of the virus a great deal,” he said.

Looking both back and forward, understanding the simple equations of transmission and extinction can provide a foundation for a positive mindset regarding the next phases in HIV research and prevention. “This kind of knowledge is worthwhile because it allows us to remember that there are actually changes that we can make now that can force the virus back into extinction,” Worobey said. “If we do everything we can in terms of rapid and widespread prevention efforts, it is realistic to think about driving the virus back into extinction, even if we never find a true vaccine. It just comes down to making it less likely that each person who is carrying the virus will transmit it to the next person.” – by Rob Volansky

For more information:

Worobey M, Gemmel M, Teuwen D. Direct evidence of extensive diversity of HIV-1 in Kinshasa by 1960. Nature. 2008;455:661-665.