{{Short description|Genus of viruses}} {{Use dmy dates|date=August 2024}} {{Virusbox | image = Pithovirus sibericum sketch.jpg | image_alt = | image_caption = ''Alphapithovirus siberiense'' | taxon = Alphapithovirus | subdivision_ranks = Species | subdivision_ref =<ref name="ICTVtax">{{cite web |title=Virus Taxonomy: 2025 Release |url=https://ictv.global/taxonomy |publisher=International Committee on Taxonomy of Viruses |access-date=23 March 2026 |language=en}}</ref> | subdivision = *''Alphapithovirus massiliense'' *''Alphapithovirus siberiense'' | synonyms = | synonyms_ref = }}

'''''Alphapithovirus''''' is a genus of giant virus known from two species, ''Alphapithovirus siberiense'', which infects amoebae,<ref name=Nature>{{cite journal |last=Yong |first=Ed |doi=10.1038/nature.2014.14801 |title=Giant virus resurrected from 69,000-year-old ice |journal=Nature |date=3 March 2014|s2cid=87146458 }}</ref><ref name="BBC 2014">{{cite news |first=Rebecca |last=Morelle |author-link=Rebecca Morelle |title=30,000-year-old giant virus 'comes back to life' |date=3 March 2014 |url=https://www.bbc.com/news/science-environment-26387276 |work=BBC News}}</ref> and ''Alphapithovirus massiliense''.<ref name=Levasseur2016>{{cite journal |vauthors=Levasseur A, Andreani J, Delerce J, Bou Khalil J, Robert C, La Scola B, Raoult D |title=Comparison of a modern and fossil Pithovirus reveals its genetic conservation and evolution |journal=Genome Biol Evol |volume= 8|issue= 8|pages= 2333–9|date=July 2016 |pmid=27389688 |doi=10.1093/gbe/evw153 |pmc=5010891}}</ref> It is DNA-based and is a member of the nucleocytoplasmic large DNA viruses clade. It was discovered in 2014, when a viable specimen was found in a 30,000-year-old ice core harvested from permafrost in Siberia, Russia. It is the third-largest known giant virus, behind only ''Megaklothovirus horridgei'' and ''Klothovirus casanovai''.

== Description == The genus name ''Alphapithovirus'', a reference to large storage containers of ancient Greece known as pithoi, was chosen to describe the new species. A specimen of ''Alphapithovirus'' measures approximately 1.5&nbsp;μm (1,500 nm) in length and 0.5&nbsp;μm (500&nbsp;nm) in diameter, making it one of the largest viruses yet found, behind only Megaklothovirus and Klothovirus in size.{{Cn|date=April 2026}} At the time of its discovery in 2014, the ''Pithovirus'' was the largest known virus by diameter. It is 50% larger in size than the ''Pandoraviridae'', the previous largest-known viruses,<ref name="NatGeo">{{cite news |title=Ancient "Giant Virus" Revived From Siberian Permafrost |work=National Geographic |date=3 March 2014 |last=Sirucek |first=Stefan |url=http://news.nationalgeographic.com/news/2014/03/140303-giant-virus-permafrost-siberia-pithovirus-pandoravirus-science/|archive-url=https://web.archive.org/web/20140304020034/http://news.nationalgeographic.com/news/2014/03/140303-giant-virus-permafrost-siberia-pithovirus-pandoravirus-science/|url-status=dead|archive-date=4 March 2014}}</ref> and is larger than ''Ostreococcus'', the smallest eukaryotic cell, although ''Pandoravirus'' has the largest viral genome, containing 1.9 to 2.5 megabases of DNA.<ref name="Brumfiel">{{cite news |url=https://www.npr.org/sections/health-shots/2013/07/18/203298244/worlds-biggest-virus-may-have-ancient-roots/ |title=World's Biggest Virus May Have Ancient Roots |work=National Public Radio |date=18 July 2013 |last=Brumfiel |first=Geoff}}</ref>

''Alphapithovirus'' has a thick, oval wall, with an opening at one end. Internally, its structure resembles a honeycomb.<ref name=Nature/>

The genome of ''Alphapithovirus'' contains 467 distinct genes, more than a typical virus, but far fewer than the 2556 putative protein-coding sequences found in ''Pandoravirus''.<ref name=NatGeo/> Thus, its genome is far less densely packed than any other known virus. Two-thirds of its proteins are unlike those of other viruses. Despite the physical similarity with ''Pandoravirus'', the ''Alphapithovirus'' genome sequence reveals that it is barely related to that virus, but more closely resembles members of ''Marseilleviridae'', ''Megaviridae'', and ''Iridoviridae''.<ref name="Virology Blog"/> These families all contain large icosahedral viruses with DNA genomes. The ''Alphapithovirus'' genome has 36% GC-content, similar to the ''Megaviridae'', in contrast to greater than 61% for pandoraviruses.<ref name="Legendre2014"/> The family ''Orpheoviridae'' and genus ''Alphaorpheovirus'', the family ''Pithoviridae'' and genus ''Alphapithovirus'', and the family ''Cedratviridae'' and genus, ''Alphacedratvirus,'' has now been ratified by the ICTV.<ref name=":1">{{cite journal |last1=Queiroz |first1=Victória F. |last2=Rodrigues |first2=Rodrigo A. L. |last3=Abrahão |first3=Jônatas Santos |title=A taxonomic proposal for cedratviruses, orpheoviruses, and pithoviruses |journal=Archives of Virology |date=June 2024 |volume=169 |issue=6 |page=132 |doi=10.1007/s00705-024-06055-x |pmid=38822903 |doi-access=free }}</ref>

=== Replication === The ''Alphapithovirus'' genome is one circular, double-stranded DNA (dsDNA) chromosome of about 610,000 base pairs (bp), encoding approximately 467 open reading frames (ORFs), which translate into 467 different proteins.<ref name='SIB'>{{cite web |url=http://viralzone.expasy.org/all_by_species/4237.html |title= Pithovirus sibericum |access-date= 10 March 2014 |work= Swiss Institute of Bioinformatics (SIB)}}</ref> The genome encodes all the proteins needed to produce mRNA; these proteins are present in the purified virions.<ref name="Virology Blog"/> Viral entry is initiated by attachment of virions to cells, leading to internalization, and uncoating to release genetic material for replication and propagation.<ref name=":0">{{cite journal |last1=Rigou |first1=Sofia |last2=Schmitt |first2=Alain |last3=Alempic |first3=Jean-Marie |last4=Lartigue |first4=Audrey |last5=Vendloczki |first5=Peter |last6=Abergel |first6=Chantal |last7=Claverie |first7=Jean-Michel |last8=Legendre |first8=Matthieu |title=Pithoviruses Are Invaded by Repeats That Contribute to Their Evolution and Divergence from Cedratviruses |journal=Molecular Biology and Evolution |date=3 November 2023 |volume=40 |issue=11 |doi=10.1093/molbev/msad244 |pmid=37950899 |pmc=10664404 }}</ref>''Alphapithovirus'' therefore undergoes its entire replication cycle in its host's cytoplasm, rather than the more typical method of taking over the host's nucleus.<ref name=Nature/><ref name="Virology Blog"/><ref name="Coghlan">{{cite news |first=Andy |last=Coghlan |title=Biggest-ever virus revived from Stone Age permafrost |date=3 March 2014 |url=https://www.newscientist.com/article/dn25151-biggestever-virus-revived-from-stone-age-permafrost.html |work=NewScientist |archive-date=5 March 2014 |archive-url=https://web.archive.org/web/20140305155750/http://www.newscientist.com/article/dn25151-biggestever-virus-revived-from-stone-age-permafrost.html |url-status=live}}</ref>

== Discovery == ''Alphapithovirus sibericum'' was discovered in a 30,000-year-old sample of Siberian permafrost by Chantal Abergel and Jean-Michel Claverie of Aix-Marseille University.<ref name=Nature/><ref>{{cite news |last=Pappas |first=Stephanie |url=https://news.yahoo.com/frozen-giant-virus-still-infectious-30-000-years-173243936.html |title=Frozen Giant Virus Still Infectious After 30,000 Years |work=Yahoo News |date=16 September 2015 |access-date=20 September 2015}}</ref> The virus was discovered buried {{convert|30|m|ft|abbr=on|sigfig=1}} below the surface of a late Pleistocene sediment.<ref name="BBC 2014"/><ref name="Virology Blog">{{cite news |first=Vincent |last=Racaniello |title=Pithovirus: Bigger than Pandoravirus with a smaller genome |date=4 March 2014 |url=http://www.virology.ws/2014/03/04/pithovirus-bigger-than-pandoravirus-with-a-smaller-genome/ |work=Virology Blog}}</ref> Called ''Pithovirus sibericum'', it belongs to a class of giant viruses that were discovered 10 years ago.<ref>{{Cite news |date=4 March 2014 |title=30,000-year-old giant virus 'comes back to life' |url=https://www.bbc.com/news/science-environment-26387276 |access-date=27 September 2024 |work=BBC News |language=en-GB}}</ref> It was found when riverbank samples collected in 2000 were exposed to amoebas.<ref name=NYT1>{{cite news |title=Out of Siberian Ice, a Virus Revived |work=The New York Times |date=3 March 2014 |first=Carl |last=Zimmer |url=https://www.nytimes.com/2014/03/04/science/out-of-siberian-ice-a-virus-revived.html}}</ref> The amoebas started dying and, when examined, were found to contain giant virus specimens. The authors said they got the idea to probe permafrost samples for new viruses after reading about an experiment that revived a similar aged seed of ''Silene stenophylla'' two years earlier.<ref name=Nature/> The ''Alphapithovirus'' findings were published in the ''Proceedings of the National Academy of Sciences'' in March 2014.<ref name=NatGeo/><ref name="Legendre2014">{{cite journal |doi= 10.1073/pnas.1320670111 |title= Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology |journal= Proc. Natl. Acad. Sci. U.S.A. |volume= 111 |issue= 11 |pages= 4274–9 |date= March 2014 |pmid= 24591590 |last1= Legendre |first1= M. |last2= Bartoli |first2= J. |last3= Shmakova |first3= L. |last4= Jeudy |first4= S. |last5= Labadie |first5= K. |last6= Adrait |first6= A. |last7= Lescot |first7= M. |last8= Poirot |first8= O. |last9= Bertaux |first9= L. |last10= Bruley |first10= C. |last11= Coute |first11= Y. |last12= Rivkina |first12= E. |last13= Abergel |first13= C. |last14= Claverie |first14= J.-M.|pmc= 3964051 |bibcode= 2014PNAS..111.4274L |doi-access= free }}</ref>

Although the virus is harmless to humans, its viability after being frozen for millennia has raised concerns that global climate change and tundra drilling operations could lead to previously undiscovered and potentially pathogenic viruses being unearthed.<ref name=NatGeo/> However, other scientists dispute that this scenario poses a real threat.<ref name=Nature/>

A modern species in the genus, ''Alphapithovirus massiliense'', was isolated in 2016. The core features such as the order of ORFs and orphan genes (ORFans) are well conserved between the two known species.<ref name=Levasseur2016/>

== Evolution == The rate of mutation of the genome has been estimated to be 2.23 × 10<sup>−6</sup> substitutions/site/year.<ref name="Duchêne2018">{{cite journal | last1 = Duchêne | first1 = S | last2 = Holmes | first2 = EC | year = 2018 | title = Estimating evolutionary rates in giant viruses using ancient genomes | journal = Virus Evol | volume = 4| issue = 1 | article-number = vey006 | doi = 10.1093/ve/vey006 | pmid = 29511572 | pmc = 5829572 | doi-access = free }}</ref> The authors have suggested that the two known Alphapithoviruses diverged around two hundred thousand years ago. The recently identified fish alphaviruses salmon pancreas disease virus and sleeping disease virus appear to be variants or subtypes of a new alphavirus species.<ref name=":1" />

== See also == {{Portal|Viruses}} * DNA virus * Largest organisms * Lists of virus taxa * Microbiology * Virology * Virus classification

== References == {{Reflist}}

== External links == * [https://viralzone.expasy.org/4237.html '''Viralzone''': Pithovirus] * {{cite web |title=''Pithovirus sibericum'' |work=NCBI Taxonomy Browser |url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=1450746 |id=1450746}}

{{Baltimore (virus classification)}} {{Taxonbar|from=Q18603785|from2=}}

Category:Nucleocytoplasmic large DNA viruses Category:Discovered cryopreserved organisms