Ancient virus challenges the previous understanding of viral biology with massive size and spacious interior. Although small to us at 1.5 micrometers long, the newly thawed Pithovirus sibericum is the largest virus ever discovered, comparable to the body of a bacterium. Discovered under 100 feet of Siberian permafrost and believed to be at least 30,000 years old, Pithovirus is causing a stir in many scientific circles, raising concern of ancient infections and turning what scientists thought they knew about single-celled organisms on its ear.
A sample of Pithovirus was placed in a petri dish with modern amoebas, which it promptly attacked and destroyed. Luckily it is not infectious to humans and seems to only be capable of attacking other small creatures such as itself. Although this is common viral behaviour, attacking and replicating inside the body of a host creature, the method it uses to accomplish this predatory task is unique to the species.
Pithovirus first garnered attention with its large size, but closer inspection showed that it had other unique properties as well. Featuring a honeycombed cork at one end of its structure, similar to the modern pandoraviruses discovered last year, the ancient virus spreads itself to other single-celled organisms by creating “factories” in the cytoplasm of the host that replicate its genes inside the target cell. Traditionally, a virus would attack another creature by waging war directly on the nucleus of the cell. The ancient virus challenges previous understanding in other ways as well, including only sharing a third of its genes with modern viruses, and featuring a vastly different internal structure.
Viruses that we are familiar with try to squeeze their DNA in bundles packed as tightly as possible into a body that is as small as possible, but Pithovirus goes another route, featuring a genome that is much smaller than the viruses of today, despite its larger size, resulting in a creature that is mostly empty. Similar structures aside, by virtue of its attack methods and internal structure, the Pithovirus is unlike anything virologists have ever seen before.
Scientists have long known that certain viruses and bacteria can survive for long periods of time in inhospitable environments, such as door knobs and toilet seats, but the ancient virus challenges previous understanding of how creatures that have lain dormant for thousands of years can be thawed and simply resume living. Researchers are sequencing the DNA of Pithovirus to get a better understanding of its abilities, but it has already made quite a mark on the community. Some researchers are concerned that as global warming contributes to melting permafrost and people begin to drill and settle in areas of Siberia that have long been uninhabited that there is a chance for viruses to be released and begin infecting them.
Despite the differences found between the genes of the ancient viruses and modern examples, ours have remained fairly unchanged in the last 30,000 years, meaning that if the right virus was to be freed from the ice, people could be exposed to the same diseases that plagued our ancestors, such as smallpox. Because these ancient virions have been out of circulation for so long our immune systems are no longer prepared to handle them, but as the ancient virus challenges previous understanding of structures and methods, many are quick to point out that we are exposed to billions of viruses and bacterium everyday.
By Daniel O’Brien