KI polyomavirus

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Human polyomavirus 3
Virus classification e
(unranked): Virus
Realm: Monodnaviria
Kingdom: Shotokuvirae
Phylum: Cossaviricota
Class: Papovaviricetes
Order: Sepolyvirales
Family: Polyomaviridae
Genus: Betapolyomavirus
Human polyomavirus 3

KI polyomavirus (also known as KI virus, KIPyV, or Human polyomavirus 3) is a virus of the family Polyomaviridae. It was discovered in 2007 in stored samples of human respiratory secretions collected by the Karolinska Institute, after which the virus is named.[1]


Among the human polyomaviruses, KI is most similar to WU virus. A 2010 proposed classification recommended the division of the polyomaviruses into three genera, containing one genus of avian viruses and two of mammalian viruses; one of the latter was designated Wukipolyomavirus to indicate its two founding members.[2] In an updated classification system for the polyomavirus family proposed in 2016, WU virus is classified as a member of the genus Betapolyomavirus along with BK, JC, and KI.[3]


Genome structure of the WU virus.[4] KI virus has a near-identical structure with a slightly different length of 5040 base pairs.[1]

The complete genome of the KI virus has been sequenced and found to be a circular double-stranded DNA genome of 5040 base pairs containing genetic material characteristic of polyomaviruses, encoding five viral proteins: three capsid components, major capsid protein VP1, VP2, and VP3; and two additional proteins involved in replication, the large tumor antigen and small tumor antigen.[1]


KI virus was discovered in 2007 in samples of human respiratory secretions being systematically searched as part of a program for identifying novel human viruses. It was identified by sequence homology to known human polyomaviruses BK virus and JC virus, and simian polyomavirus SV40.[1]

KI virus was the third human polyomavirus described and the first to be discovered since BK and JC in 1971.[3]

A very similar respiratory virus, WU virus, was also reported later in 2007.[4]


KI virus got its name from the Karolinska Institute, the institutional affiliation of the researchers who discovered and reported the virus.[1]


Schematic representation of the human body showing the organs to which each human polyomavirus has tropism [5]

KI virus, like its close relative WU virus, is not known to be associated with any clinical disease despite its presence in respiratory secretions.[6] The rate of co-infection with other respiratory viruses is high, so it is difficult to assign causality to KI virus even where clinical symptoms are present.[7] Some polyomaviruses are well known as carcinogenic, including the human polyomavirus Merkel cell polyomavirus, but KI virus has also not been associated with cancer.[8] While no clear association with clinical symptoms has been identified, there is weak indication that WU and KI viruses may have pathogenic potential in immunocompromised patients.[9]


The prevalence of KI virus as detected by the presence of its DNA in human samples is generally estimated in the 1-5% range in various locations and populations, with some indication of age-dependence.[7] The virus has been detected in the respiratory secretions of children with respiratory infections in multiple locations.[10][11] By contrast, one 2009 study placed seroprevalence - that is, prevalence of antibodies against the virus (in this case the VP1 coat protein) - as high as 55% among a population of American adults and 56% among a population of American children.[12] Another 2009 study found around 70% seroprevalence for adults, with age patterns indicating that infants may inherit maternal antibodies against both WU and KI.[13] A 2016 study of polyomavirus seroprevalence found WU virus in 91.3% of samples from another American population.[14] Primary infection is generally believed to occur in childhood.[14]


  1. 1.0 1.1 1.2 1.3 1.4 Allander, Tobias; Andreasson, Kalle; Gupta, Shawon; Bjerkner, Annelie; Bogdanovic, Gordana; Persson, Mats A. A.; Dalianis, Tina; Ramqvist, Torbjörn; Andersson, Björn (2007-04-01). "Identification of a third human polyomavirus". Journal of Virology. 81 (8): 4130–4136. doi:10.1128/JVI.00028-07. ISSN 0022-538X. PMC 1866148. PMID 17287263.
  2. Johne, R; Buck, CB; Allander, T; Atwood, WJ; Garcea, RL; Imperiale, MJ; Major, EO; Ramqvist, T; Norkin, LC (September 2011). "Taxonomical developments in the family Polyomaviridae". Archives of Virology. 156 (9): 1627–34. doi:10.1007/s00705-011-1008-x. PMC 3815707. PMID 21562881.
  3. 3.0 3.1 Polyomaviridae Study Group of the International Committee on Taxonomy of, Viruses; Calvignac-Spencer, S; Feltkamp, MC; Daugherty, MD; Moens, U; Ramqvist, T; Johne, R; Ehlers, B (June 2016). "A taxonomy update for the family Polyomaviridae". Archives of Virology. 161 (6): 1739–50. doi:10.1007/s00705-016-2794-y. hdl:10037/13151. PMID 26923930.
  4. 4.0 4.1 Gaynor, AM; Nissen, MD; Whiley, DM; Mackay, IM; Lambert, SB; Wu, G; Brennan, DC; Storch, GA; Sloots, TP; Wang, D (4 May 2007). "Identification of a novel polyomavirus from patients with acute respiratory tract infections". PLOS Pathogens. 3 (5): e64. doi:10.1371/journal.ppat.0030064. PMC 1864993. PMID 17480120.
  5. White, Martyn K.; Gordon, Jennifer; Khalili, Kamel (14 March 2013). "The Rapidly Expanding Family of Human Polyomaviruses: Recent Developments in Understanding Their Life Cycle and Role in Human Pathology". PLoS Pathogens. 9 (3): e1003206. doi:10.1371/journal.ppat.1003206. ISSN 1553-7366.
  6. Norja, P; Ubillos, I; Templeton, K; Simmonds, P (December 2007). "No evidence for an association between infections with WU and KI polyomaviruses and respiratory disease". Journal of Clinical Virology. 40 (4): 307–11. doi:10.1016/j.jcv.2007.09.008. PMC 7172997. PMID 17997354.
  7. 7.0 7.1 Abedi Kiasari, B; Vallely, PJ; Corless, CE; Al-Hammadi, M; Klapper, PE (September 2008). "Age-related pattern of KI and WU polyomavirus infection". Journal of Clinical Virology. 43 (1): 123–5. doi:10.1016/j.jcv.2008.05.003. PMC 7108349. PMID 18573691.
  8. Dalianis, T; Hirsch, HH (15 March 2013). "Human polyomaviruses in disease and cancer". Virology. 437 (2): 63–72. doi:10.1016/j.virol.2012.12.015. PMID 23357733.
  9. Babakir-Mina, M; Ciccozzi, M; Perno, CF; Ciotti, M (August 2013). "The human polyomaviruses KI and WU: virological background and clinical implications". APMIS. 121 (8): 746–54. doi:10.1111/apm.12091. PMID 23782405. S2CID 38133334.
  10. Yuan, XH; Jin, Y; Xie, ZP; Gao, HC; Xu, ZQ; Zheng, LS; Zhang, RF; Song, JR; Hou, YD; Duan, ZJ (October 2008). "Prevalence of human KI and WU polyomaviruses in children with acute respiratory tract infection in China". Journal of Clinical Microbiology. 46 (10): 3522–5. doi:10.1128/jcm.01301-08. PMC 2566089. PMID 18667596.
  11. Bialasiewicz, S; Whiley, DM; Lambert, SB; Wang, D; Nissen, MD; Sloots, TP (September 2007). "A newly reported human polyomavirus, KI virus, is present in the respiratory tract of Australian children". Journal of Clinical Virology. 40 (1): 15–8. doi:10.1016/j.jcv.2007.07.001. PMC 7172449. PMID 17706457.
  12. Kean, JM; Rao, S; Wang, M; Garcea, RL (March 2009). "Seroepidemiology of human polyomaviruses". PLOS Pathogens. 5 (3): e1000363. doi:10.1371/journal.ppat.1000363. PMC 2655709. PMID 19325891.
  13. Nguyen, Nang L.; Le, Binh Minh; Wang, David (2009-08-01). "Serologic evidence of frequent human infection with WU and KI polyomaviruses". Emerging Infectious Diseases. 15 (8): 1199–1205. doi:10.3201/eid1508.090270. ISSN 1080-6059. PMC 2815979. PMID 19751580.
  14. 14.0 14.1 Gossai, A; Waterboer, T; Nelson, HH; Michel, A; Willhauck-Fleckenstein, M; Farzan, SF; Hoen, AG; Christensen, BC; Kelsey, KT; Marsit, CJ; Pawlita, M; Karagas, MR (1 January 2016). "Seroepidemiology of Human Polyomaviruses in a US Population". American Journal of Epidemiology. 183 (1): 61–9. doi:10.1093/aje/kwv155. PMC 5006224. PMID 26667254.