Mimiviridae

The first member of this family, Mimivirus, was discovered in 2003,^[6] and the first complete genome sequence was published in 2004.^[7] However, the mimivirus Cafeteria roenbergensis virus^[8] was isolated and partially characterized in 1995,^[9] although the host was misidentified at the time, and the virus was designated BV-PW1.^[8]

Group: dsDNA

Family Mimiviridae is currently divided into three subfamilies.^[2][3][10]

• One subfamily (genus Mimivirus, proposed names: Megavirinae or Megamimivirinae) is divided into three "lineages":
  • A — Mimivirus group: includes Acanthamoeba polyphaga Mimivirus, Hirudovirus, Mamavirus, Kroon virus, Lentille virus, Terra2, Niemeyer virus, Samba virus.^[11][12]
  • B — Moumouvirus group: includes Moumouvirus, Saudi moumouvirus, Moumouvirus goulette, Monve virus (aka Moumouvirus monve), and Ochan virus.^{[13][11][14][12]}
  • C — Courdo11 virus group: includes Mont1,^[11] Courdo7, Courdo11, Megavirus chilensis, LBA111, Powai lake megavirus and Terra1.^[15][16]

The majority of Mimiviridae appear to belong to this subfamily (Mimiviruses).^[10]

It is sometimes also referred to as Mimiviridae group I.^[17]

• The second subfamily (Cafeteriavirus or Mimiviridae group II) includes the Cafeteria roenbergensis virus (CroV).^[8]
• The Klosneuvirinae have been proposed as a third subfamily and are divided into four "lineages": Klosneuvirus, Indivirus, Catovirus and Hokovirus.^[3] They seem to be closely related to the Mimivirus subfamily rather than the Cafeteriavirus subfamily (and so might be summarized in Mimivirus group I as well).^[3] The first isolate from this group is Bodo saltans virus infecting the kinetoplastid Bodo saltans.^[18]
• Tupanvirus strains have been discussed to comprise a sister group of mimiviruses.^[4]

Furthermore, it has been proposed either to extend Mimiviridae by an additional tentative group III (subfamily Mesomimivirinae) or to classify this group as a sister family Mesomimiviridae instead,^[19] comprising legacy OLPG (Organic Lake Phycodna Group). This extension (or sister family) may consist of the following:

• Phaeocystis globosa virus (PgV, represented by PgV-16T strain) and Phaeocystis pouchetii virus (PpV, e. g. PpV 01)
• "Organic Lake Phycodnavirus" 1 and 2 (OLV1, OLV2, hosts of Organic Lake virophage)
• "Yellowstone Lake Mimivirus"^[12][20] aka "Yellowstone Lake Phycodnavirus" 4 (YSLGV4)
• Chrysochromulina ericina virus (CeV, e. g. CeV 01)
• Aureococcus anophagefferens virus (^[21] AaV)
• Pyramimonas orientalis virus (PoV)
• Tetraselmis virus (TetV-1)^[22]

This group seems to be closely related to Mimiviridae rather than to Phycodnaviridae and therefore is sometimes referred to as a further subfamily candidate Mesomimivirinae. Sometimes the extended family Mimiviridae is referred to as Megaviridae although this has not been recognized by ICTV; alternatively the extended group may be referred to just as Mimiviridae.^{[3][23][24][25][26][17]}

With recognition of new order Imitervirales by the ICTV in March 2020 there is no longer need to extend the Mimiviridae family to comprise a group of viruses of the observed high diversity. Instead, the extension (or at least its main clade) may be referred to as a sister family Mesomimiviridae.^[19]

Although only a couple of members of this order have been described in detail it seems likely there are many more awaiting description and assignment^[27][28] Unassigned members include Aureococcus anophagefferens virus (AaV), CpV-BQ2 and Terra2.^{[citation needed]}

^[18] Viruses in Mimiviridae have icosahedral and round geometries, with between T=972 and T=1141, or T=1200 symmetry. The diameter is around 400 nm, with a length of 125 nm. Genomes are linear and non-segmented, around 1200kb in length. The genome has 911 open reading frames.^[1]

Replication follows the DNA strand displacement model. DNA-templated transcription is the method of transcription. Amoeba serve as the natural host.^[1]

Three putative DNA base excision repair enzymes were characterized from Mimivirus.^[29] The base excision repair (BER) pathway was experimentally reconstituted using the purified recombinant proteins uracil-DNA glycosylase (mvUDG), AP endonuclease (mvAPE), and DNA polymerase X protein (mvPolX).^[29] When reconstituted in vitro mvUDG, mvAPE and mvPolX function cohesively to repair uracil-containing DNA predominantly by long patch base excision repair, and thus these processes likely participate in the BER pathway early in the Mimivirus life cycle.^[29]

Mimiviruses have been associated with pneumonia but their significance is currently unknown.^[30] The only virus of this family isolated from a human to date is LBA 111.^[31] At the Pasteur Institute of Iran (Tehran), researchers identified mimivirus DNA in bronchoalveolar lavage (BAL) and sputum samples of a child patient, utilizing real-time PCR (2018).  Analysis reported 99% homology of LBA111, lineage C of the Megavirus chilensis.^[32] With only a few reported cases previous to this finding, the legitimacy of the mimivirus as an emerging infectious disease in humans remains controversial.^[33][34]

Mimivirus has also been implicated in rheumatoid arthritis.^[35]

• Virophage

Wikispecies has information related to Mimiviridae.

• Viralzone: Mimiviridae
• ICTV