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'Fossil' HIV reveals virus history

A preserved specimen of lymph node nearly half a century old has revealed how rapidly the HIV virus has diversified, according to international research.

A team of researchers from around the world has been trawling through decades-old tissue samples from African hospital archives in the hope of finding samples containing the HIV virus.

They struck it lucky with a sample that was collected back in 1960, from a woman living in what is now the Democratic Republic of Congo.

This is the second-oldest sample of the HIV virus ever found - the oldest is from 1959.

The researchers found that the HIV viral sequences these two samples differ significantly in their genetic makeup.

Their finding appears in the latest issue of Nature.

Using a technique called molecular clock analysis, they were able to plot the two viral sequences' evolutionary path back in time to determine when they diverged.

They concluded the strains evolved from a common ancestor that emerged in Africa near the beginning of the twentieth century around 80 years before the disease appeared in western populations.

Fossil virus

Co-researcher and molecular palaeontologist Dr Michael Bunce, head of the Ancient DNA Laboratory at Murdoch University, Perth, says these early viral sequences tell scientists a lot about how the virus evolves.

"The more information we can find out about the evolutionary history of pathogens, [the] more we can understand how they've changed over time to adapt to humans," says Bunce.

"We can get a really good picture of those parts of the virus that are rapidly mutating and those that stay more constant."

While a 50-year-old sample seems relatively young compared to the fossil materials Bunce is used to working with, for a virus like HIV, it's ancient.

"HIV mutates so quickly that 40 to 50 years old is really akin to looking at fossil bone that's millions of years old," he says.

Extracting the viral genetic material from the samples was no easy task. The samples had been preserved in formalin, which can cause considerable damage to DNA sequences.

"What we have got is actually quite good considering the preservation status," Bunce says, but it required a lot of technological 'tweaking' to isolate the tiny snippets of DNA from the sample.

The international research team is continuing to analyse hundreds of samples in the hope of finding further HIV-positive tissue that could add more pieces to the puzzle.