A 30,000-year-old giant virus has been revived from the frozen Siberian tundra, sparking concern that increased mining and oil drilling in rapidly warming northern latitudes could disturb dormant microbial life that could one day prove harmful to man.
The latest find, described online in the Proceedings of the National Academy of Sciences, appears to belong to a new family of mega viruses that infect only amoeba.
But its revival in a laboratory stands as "a proof of principle that we could eventually resurrect active infectious viruses from different periods", said the study's lead author, microbiologist Professor Jean-Michel Claverie of Aix-Marseille University in France.
"We know that those non-dangerous viruses are alive there, which probably is telling us that the dangerous kind that may infect humans and animals - that we think were eradicated from the surface of earth - are actually still present and eventually viable, in the ground," Claverie said.
With global warming making northern reaches more accessible, the chance of disturbing dormant human pathogens increased, the researchers concluded.
Average surface temperatures in the area that contained the virus had increased more steeply than in more temperate latitudes, the researchers noted.
"People will go there; they will settle there, and they will start mining and drilling," Claverie said. "Human activities are going to perturb layers that have been dormant for 3 million years and may contain viruses."
Claverie's co-author, Dr Chantal Abergel, nonetheless cautioned that their finding was limited to one innocuous virus infecting an amoeba. "We cannot definitely say that there are some human pathogens in there," she said.
They would re-examine the drill core samples, Abergel said, to "find out if there is anything there that is dangerous to humans and animals".
Claverie's laboratory was behind the discovery, in Chile more than a decade ago, of the first giant DNA virus, dubbed Mimivirus. They next identified a far larger virus of an entirely different family in 2011, dubbing it Pandoravirus salinus, in homage to the mythical Pandora's box that first unleashed evil on the world.
This time, they used an amoeba common to soil and water as bait to draw out a virus from a Siberian permafrost core.
The finding described on Monday looked like another Pandora, but it was 50 per cent larger.
"Giant" in virology is still pretty tiny. A virus of one micron in size, or a thousandth of a millimetre, is considered huge. That is big enough to be seen with a normal light microscope. HIV, the virus that causes Aids, measures one tenth of a micron.
The researchers plan to re-examine large viruses that have been mistaken for bacteria in the past - one such specimen, found in 2008, had infected an amoeba living in a 17-year-old's contact-lens solution.
They also plan to look more deeply into the Siberian ice cores. "We have a sample that dates to 3 million years old," Abergel said.
Those samples could harbour ancient forms of relatively modern human pathogens, including smallpox, which was rampant in Siberia.
Fragments of a smallpox virus, for example, have been identified in Siberian mummies dating from the late 17th century.
"I would not be surprised that those viruses are still in the ground," Claverie said.
Hopes for an HIV breakthrough
Scientists in South Africa have mapped the evolution of an antibody that kills different strains of HIV, which might yield a vaccine, the country's National Institute of Communicable Diseases said.
The scientists have been studying one woman's response to HIV infection from stored samples of her blood and isolated the antibodies that she developed, said Professor Lynn Morris, head of the virology unit at the NICD. The study, by the NICD, local universities and the US Vaccine Research Centre of the National Institute of Allergy and Infectious Diseases, was published on Monday in the journal Nature.
Humans respond to HIV by producing antibodies to fight the virus. In most cases, the antibodies do not neutralise, or kill, different strains of the virus. But a few known as "broadly neutralising antibodies" are able to break through a protective layer around the HIV virus and kill it.
"The outer covering of HIV has a coating of sugars that prevents antibodies from reaching the surface to neutralise the virus. In this patient, we found that her antibodies had 'long arms', which enabled them to reach through the sugar coat that protects HIV," Dr Penny Moore, one of the lead scientists, said.
The researchers plan to see if the antibodies can give immunity to a person without the virus. Human tests are at least two years away.