PREHISTORIC viruses are lying dormant in the polar ice caps-and a bout of warm weather could release them into the atmosphere, sparking new epidemics. This chilling warning follows the discovery, for the first time, of an ancient virus in Arctic ice.
The virus, found deep within the Greenland icepack, is known as a tomato mosaic tobamovirus (ToMV), a common plant pathogen. The discovery suggests that other viruses, such as ancient strains of flu, polio and smallpox, may also be entombed and could make a comeback. "We don't know the survival rate, or how often they get back into the environment. But it certainly is possible," says Tom Starmer of Syracuse University in New York.
Starmer's colleagues Scott Rogers and John Castello of the State University of New York in Syracuse had earlier found ToMV in clouds and fog. The virus can survive in such environments because it belongs to a family with particularly tough protein coats. "Since it's widespread, moves in the atmosphere and is very stable, we deduced that we would find it in the Arctic ice," says Rogers.
So under sterile conditions, the researchers examined four cores containing ice between 500 and 140 000 years old from three sites in Greenland. To prevent contamination, they first disinfected the outside of each core using ultraviolet light, then searched the inner core for RNA from the tomato pathogen using the polymerase chain reaction (PCR). Sure enough, the telltale RNA was present. What's more, sequencing revealed 15 strains of the virus (Polar Biology, vol 22, p 207).
The frozen viruses were probably still infectious. PCR destroys organisms as it amplifies their genetic material, so the researchers can't be sure the viruses had retained the protein coats that help them invade cells. But Castello says they probably needed their coats to survive for hundreds of years in the ice.