Paleovirology is the study of viruses that existed in the past but are now extinct. In general, viruses cannot leave behind physical fossils, therefore indirect evidence is used to reconstruct the past. For example, viruses can cause evolution of their hosts, and the signatures of that evolution can be found and interpreted in the present day. Also, some viral genetic fragments which were integrated into

germline In biology and genetics, the germline is the population of a multicellular organism's cells that pass on their genetic material to the progeny ( offspring). In other words, they are the cells that form the egg, sperm and the fertilised egg. T ...

cells of an ancient organism have been passed down to our time as viral fossils, or

endogenous viral element An endogenous viral element (EVE) is a DNA sequence derived from a virus, and present within the germline of a non-viral organism. EVEs may be entire viral genomes (proviruses), or fragments of viral genomes. They arise when a viral DNA sequence b ...

s (EVEs). EVEs that originate from the integration of

retroviruses A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase ...

are known as endogenous retroviruses, or ERVs, and most viral fossils are ERVs. They may preserve genetic code from millions of years ago, hence the "fossil" terminology, although no one has detected a virus in mineral

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s. The most surprising viral fossils originate from non-retroviral DNA and

RNA virus An RNA virus is a virusother than a retrovirusthat has ribonucleic acid ( RNA) as its genetic material. The nucleic acid is usually single-stranded RNA (ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA viruse ...

es.

Terminology

Although there is no formal classification system for EVEs, they are categorised according to the taxonomy of their viral origin. Indeed, all known viral genome types and replication strategies, as defined by the

Baltimore classification Baltimore classification is a system used to Virus classification, classify viruses based on their manner of messenger RNA (mRNA) synthesis. By organizing viruses based on their manner of mRNA production, it is possible to study viruses that beha ...

, have been found in the genomic fossil record. Acronyms have been designated to describe different types of viral fossil. *EVE:

Endogenous viral element An endogenous viral element (EVE) is a DNA sequence derived from a virus, and present within the germline of a non-viral organism. EVEs may be entire viral genomes (proviruses), or fragments of viral genomes. They arise when a viral DNA sequence b ...

*ERV:

Endogenous retrovirus Endogenous retroviruses (ERVs) are endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. They are abundant in the genomes of jawed vertebrates, and they comprise up to 5–8% of the human genome (l ...

*HERV: Human Endogenous Retrovirus *NIRV: Viral fossils originating from non-retroviral RNA viruses have been termed Non-retroviral Integrated RNA Viruses or NIRVs. Unlike other types of viral fossils, NIRV formation requires borrowing the integration machinery that is coded by the host genome or by a co-infecting retrovirus. Other viral fossils originate from DNA viruses such as

hepadnavirus ''Hepadnaviridae'' is a family of viruses. Humans, apes, and birds serve as natural hosts. There are currently 18 species in this family, divided among 5 genera. Its best-known member is hepatitis B virus. Diseases associated with this family i ...

es (a group that includes

hepatitis B Hepatitis B is an infectious disease caused by the ''Hepatitis B virus'' (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection. Many people have no symptoms during an initial infection. For ...

)."Ancient "Fossil" Virus Shows Infection to Be Millions of Years Old"
by Katherine Harmon, ''

Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it ...

,'' September 29, 2010

Resurrection

Successful attempts to "resurrect" extinct viruses from the DNA fossils have been reported."How to Resurrect an Extinct Retrovirus"
''

,'' November 2, 2006 In addition, ''Pithovirus sibericum'' was revived from a 30,000-year-old

ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains i ...

harvested from

permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part o ...

, Russia.

References

{{Reflist, 2 Virology

Virology Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, thei ...

Terminology

Resurrection

See also

References