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Virus

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Viruses are minute infectious agents that are neither composed of cells, nor meet the standard definitions of living things. Viruses are acellular complex structures, that exist as viral particles outside of host cells, and as parasite-like molecular complexes within host cells. Viral particles consist of nucleic acid surrounded by a protein coat. Some viruses have a membranous envelope, composed of lipids and proteins, around the capsid; others are "naked".

1 Types
2 Classification of human viruses and viral zoonoses
3 DNA Viruses
- 3.1 Group I: dsDNA Viruses
  - 3.1.1 Enveloped Group I (dsDNA) Viruses
  - 3.1.2 Naked Group I (dsDNA) Viruses
- 3.2 Group II: ssDNA Viruses
4 RNA Viruses
5 Reverse Transcribing Viruses
- 5.1 Group VI: ssRNA-RT Viruses
- 5.2 Group VII: dsDNA-RT Viruses
6 References
7 External Links

Types

David Baltimore^[1] proposed a popular classification scheme based on the nature of the viral genome and its mode of replication:

Group I: dsDNA viruses
Group II: ssDNA viruses
Group III: dsRNA viruses
Group IV: (+)ssRNA viruses
Group V: (-)ssRNA viruses
Group VI: ssRNA-RT viruses
Group VII: dsDNA-RT viruses

Classification of human viruses and viral zoonoses

The International Committee on Taxonomy of Viruses has established naming conventions and is developing a viral classification. The sections below contain a classification of human viruses and animal viruses that can cause human disease (zoonoses).

DNA Viruses

Groups I and II include DNA viruses that are dependent upon host DNA and RNA polymerase enzymes for replication. Most therefore replicate within the host cell's nucleus. Except for Pox viruses, the capsids of DNA viruses usually have icosahedral symmetry.

Group I: dsDNA Viruses

Double-stranded DNA viruses

Enveloped Group I (dsDNA) Viruses

family: Poxviridae (capsid has a complex symmetry)
- genus: Orthopoxvirus
  - Variola virus (VARV) - small pox
  - Vaccinia virus (VACV) - laboratory strains (origin unclear, horses? cows?)
  - Cowpox virus (CPXV) - zoonosis from cats and cows
  - Monkeypox virus (MPXV)
- genus: Parapoxvirus
  - Orf virus (ORFV) - zoonosis from sheep and goats
  - Pseudocowpox virus (PCPV)
  - Bovine papular stomatitis virus (BPSV)
- genus: Molluscipoxvirus
  - Molluscum contagiosum virus (MOCV)
- genus: Yatapoxvirus
  - Tanapox virus (TANV)
  - Yaba monkey tumor virus (YMYV)

family: Herpesviridae
- subfamily: Alphaherpesvirinae
  - genus: Simplexvirus
    - HHV-1 - Herpes simplex virus 1 (HSV-1) - oral and genital herpes
    - HHV-2 - Herpes simplex virus 2 (HSV-2) - genital and oral herpes
  - genus: Varicellovirus
    - HHV-3 - Varicella zoster virus (VZV) - chickenpox, shingles
- subfamily: Betaherpesvirinae
  - genus: Cytomegalovirus
    - HHV-5 - Human cytomegalovirus (CMV) - infectious mononucleosis-like syndrome
  - genus: Roseolovirus
    - HHV-6 - sixth disease (roseola infantum, exanthem subitum)
    - HHV-7 - sixth disease
- subfamily: Gammaherpesvirinae
  - genus: Lymphocryptovirus
    - HHV-4 - Epstein-Barr virus (EBV) - infectious mononucleosis
  - genus: Rhadinovirus
    - HHV-8 - Kaposi's sarcoma-associated herpesvirus (KSHV)

Naked Group I (dsDNA) Viruses

family: Adenoviridae (including human adenoviruses - more than 50 serotypes grouped in six species - which can cause cause respiratory disease, diarrhea, conjunctivitis.)
- genus: Mastadenovirus
  - HAdV-A
  - HAdV-B
  - HAdV-C
  - HAdV-D
  - HAdV-E
  - HAdV-F

family: Papillomaviridae (including more than 100 Human Papillomaviruses in 5 or more genera, well known for causing warts, condylomata acuminata, and genital malignancies, e.g., cervical cancer.)
- genus: Alphapapillomavirus - preferentially infect the oral or anogenital mucosa
  - some are high-risk for malignancy (e.g., HPV-16 & HPV-18)
  - some in cutaneous lesions (e.g., HPV-2 & HPV-10)
- genus: Betapapillomavirus - cutaneous lesions
  - HPV-5, HPV-9, HPV-49 - associated with epidemodysplasia verruciformis
- genus: Gammapapillomavirus - cutaneous lesions
  - HPV-4, HPV-48, HPV-50, HPV-60, HPV-80
- genus: Mupapillomavirus - cutaneous lesions
  - HPV-1, HPV-63
- genus: Nupapillomavirus
  - HPV-41

family: Polyomaviridae
- genus: Polyomavirus
  - BK polyomavirus (BKPyV)
  - JC polyomavirus (JCPyV) - progressive multifocal leucoencephalopathy
  - Human polyomavirus (HPyV)
  - Simian vacuolating virus 40 (SV40)
  - Merkel cell polyomavirus - likely causative agent of Merkel skin cancer
  - KI polyomavirus
  - WU polyomavirus

Group II: ssDNA Viruses

Single-stranded, positive-sense DNA viruses

family: Parvoviridae - naked, capsid has icosahedral symmetry
- genus: Erythrovirus
  - Parvovirus B19 (B19V) - fifth disease (erythema infectiosum)

family: Circoviridae - naked, capsid has icosahedral symmetry
- genus: Anellovirus
  - Transfusion Transmitted Virus (TTV) - non-pathogenic?

RNA Viruses

Group III, IV, and V viruses include RNA viruses that use their own RNA replicase enzymes for replication. RNA viruses usually replicate in the cytoplasm of their host cell.

Group III: dsRNA Viruses

Double-stranded RNA viruses

family: Reoviridae - family of naked, icosahedral viruses that affect the alimentary and respiratory systems (REOviruses = "respiratory enteric orphan" viruses)
- genus: Orthoreovirus
  - Mammalian orthoreovirus (MRV)
- genus: Orbivirus
  - African horse sickness virus (AHSV)
  - Changuinola virus (SRAV)
  - Carriparta virus (CORV)
  - Orungo virus (ORUV)
- genus: Rotavirus - the leading cause of severe diarrhea in infants and young children worldwide
  - Rotavirus A (RV-A) - causes 90% of human rotavirus gastroenteritis
  - Rotavirus B (RV-B)
  - Rotavirus C (RV-C)
- genus: Coltivirus
  - Colorado tick fever virus

Group IV: (+)ssRNA viruses

Single-stranded, positive-sense RNA viruses. Except for Coronaviruses, the capsids of human Group IV viruses usually have icosahedral symmetry.

Naked Group IV (+)ssRNA Viruses

family: Picornaviridae
- genus: Enterovirus - infect gastrointestinal tract
  - Human enterovirus A (HEV-A) - some coxsackie A viruses and other enteroviruses
  - Human enterovirus B (HEV-B) - coxsackie B viruses and echoviruses
  - Human enterovirus C (HEV-c) - some coxsackie A viruses
  - Human enterovirus D (HEV-D) - EV-68, EV-70, EV-94
  - Poliovirus (PV) - PV-1, PV-2, PV-3
- genus: Rhinovirus - infect nose and throat
  - Human rhinovirus A (HRV-A) - common cold (more than 70 serotypes)
  - Human rhinovirus B (HRV-B) - common cold (more than 20 serotypes)
- genus: Hepatovirus
  - Hepatitis A virus (HAV)
- genus: Parechovirus
  - Human parechovirus (HPeV)
- genus: Cardiovirus
  - Encephalomyocarditis virus (EMCV)
  - Theilovirus - includes Vilyuisk human encephalomyelitis virus and Saffold viruses
- genus: Kobuvirus
  - Aichi virus (AiV)
family: Caliciviridae
- genus: Norovirus
  - Norwalk virus (NV) - gastroenteritis
- genus: Sapovirus
  - Sapporo virus (SV) - gastroenteritis
family: Unassigned - similar to Caliciviridae
- gensu: Hepevirus
  - Hepatitis E virus (HEV) - acute hepatitis
family: Astroviridae
- genus: Mamastrovirus
  - Human astrovirus (HAstV) - gastroenteritis in children and adults

Enveloped Group IV (+)ssRNA Viruses

family: Togaviridae
- genus: Alphavirus - mosquito vectors (Arboviruses)
  - Chikungunya virus (CHIKV)
  - O'nyong-nyong virus (ONNV)
  - Mayaro virus (MAYV)
  - Ross River virus (RRV)
  - Barmah Forest virus (BFV)
  - Sindbis virus (SINV)
  - Semliki Forest virus
  - Ockelbo virus
  - Venezuelan equine encephalitis virus (VEEV)
  - Western equine encephalitis virus (WEEV)
  - Eastern equine encephalitis virus (EEEV)
- genus: Rubivirus
  - Rubella virus - German measles

family: Flaviviridae
- genus: Flavivirus
  - Tick-borne viruses (Arboviruses)
    - Kyasanur Forest disease virus (KFDV)
    - Omsk hemorrhagic fever virus (OHFV)
    - Powassan virus (POWV)
    - Louping ill virus (LIV)
    - Tick-borne encephalitis virus (TBEV)
  - Mosquito-borne viruses (Arboviruses)
    - Dengue virus (DENV)
    - Japanese encephalitis virus (JEV)
    - Murray Valley encephalitis virus (MVEV)
    - St. Louis encephalitis virus (SLEV)
    - West Nile virus (WNV)
    - Ilheus virus
    - Yellow fever virus (YFV)
  - No known arthropod vector
    - Apoi virus (APOIV)
- genus: Hepacivirus
  - Hepatitis C virus
  - GB virus B (GBV_B)
- genus: Unassigned
  - GB virus A (GBV-A)
  - GB virus C (GBV-C) - "Hepatitis G virus"

family: Coronaviridae - capsid has helical symmetry
- genus: Coronavirus - respiratory and gastrointestinal tract
  - Group 1 (including HCoV-229E, HCoV-NL63/NL/New Haven)
  - Group 2 (including HCoV-OC43, HCoV-HKU1, SARS-CoV, HECoV)
- genus: Torovirus
  - Human torovirus

Group V: (-)ssRNA viruses

Single-stranded, negative-sense RNA viruses. Human Group V are enveloped viruses. Except for Arenaviruses and Hepatitis D virus, the capsids of human Group V viruses have helical symmetry

family: Arenaviridae - capsids have icosahedral symmetry
- genus: Arenavirus - zoonoses, usually associated with rodents
  - Old World complex
    - Lassa virus (LASV)
    - Lymphocytic choriomeningitis virus (LCMV)
  - New World complex
    - Guanarito virus (GTOV)
    - Junin virus (JUNV)
    - Machupo virus (MACV)
    - Sabiá virus (SABV)
    - Chapare virus
    - Tacaribe virus
    - Flexal virus
    - Whitewater Arroyo virus

family: Orthomyxoviridae
- genus: Influenzavirus A
  - Influenza A virus (FLUAV)
- genus: Influenzavirus B
  - Influenza B virus (FLUBV)
- genus: Influenzavirus C
  - Influenza C virus (FLUCV)
- genus: Thogotovirus
  - Thogoto virus (THOV)
  - Dhori virus (DHOV)

family: Bunyaviridae
- genus: Bunyavirus - Arboviruses
  - Bunyamwera virus (BUNV)
  - Bwamba virus (BWAV)
  - California encephalitis virus (CEV; includes La Crosse virus)
  - Guama virus (GMAV)
  - Oriboca virus (ORIV)
  - Oropouche virus (OROV)
- genus: Hantavirus - rodent reservoirs
  - Hemorrhagic fever with renal syndrome
    - Hantaan virus (HTNV) - Korean hemorrhagic fever
    - Puumala virus (PUUV)
    - Seoul virus (SEOV)
    - Dobrava-Belgrade virus (DOBV)
  - Hantavirus cardiopulmonary syndrome
    - Sin Nombre virus (SNV)
    - Andes virus (ANDV) - HCPS
    - Laguna Negra virus
    - Bayou virus (BAYV)
    - Black Creek Canal virus (BCCV)
    - New York virus (NYV)
- genus: Nairovirus - Arboviruses (tick-borne)
  - Crimean-Congo hemorrhagic fever virus (CCHFV)
  - Nairobi sheep disease virus (NSDV, a Dugbe virus strain)
- genus: Phlebovirus - Arboviruses (e.g., sandflies)
  - Rift Valley fever virus (RVFV)
  - Sandfly fever Naples virus (SFNV; includes Toscana virus)
  - Sandfly fever Sicilian virus
  - Chandiru virus (includes Alenquer virus)
  - Punta Toro virus
  - Chagres virus

family: Unassigned
- genus: Deltavirus - a viroid-like agent with a non-segmented genome
  - Hepatitis delta virus (HDV) - "Hepatitis D virus"

order: Mononegavirales (non-segmented (-)ssRNA viruses)

family: Paramyxoviridae
- - subfamily: Paramyxovirinae
    - genus: Respirovirus
      - Human parainfluenza virus 1 (HPIV-1)
      - Human parainfluenza virus 3 (HPIV-3)
    - genus: Morbillivirus
      - Measles virus
    - genus: Rubulavirus
      - Human parainfluenza virus 2 (HPIV-2)
      - Human parainfluenza virus 4 (HPIV-4)
      - Mumps virus (MuV)
      - Menangle virus - zoonosis from fruit bats
      - Tioman virus - suspected zoonosis from fruit bats
    - genus: Henipavirus
      - Hendravirus - zoonosis from fruit bats
      - Nipahvirus - zoonosis from fruit bats
  - subfamily: Pneumovirinae
    - genus: pneumovirus
      - Human respiratory syncytial virus (HRSV)
    - genus: Metapneumovirus
      - Human metapneumovirus (HMPV)

family: Rhabdoviridae
- genus: Lyssavirus - zoonotic encephalitis
  - Rabies virus (RABV)
  - Australian bat lyssavirus (ABLV)
- genus: Vesiculovirus
  - Chandipura virus (CHPV)
  - Cocal virus (COCV)
  - Isfahan virus (ISFV)
  - Piry virus (PIRYV)
  - Vesicular stomatitis Alagoas virus (VSAV)
  - Vesicular stomatitis Indiana virus (VSIV)
  - Vesicular stomatitis New Jersey virus (VSNJV)

family: Filoviridae
- genus: Marburgvirus
  - Lake Victoria marburgvirus - zoonosis from nonhuman primates and fruit bats
- genus: Ebolavirus - zoonosis from nonhuman primates (and fruit bats?)
  - Zaire ebolavirus
  - Ivory Coast ebolavirus
  - Reston ebolavirus
  - Sudan ebolavirus
  - Bundibugyo ebolavirus

family: Bornaviridae
- genus: Bornavirus
  - Borna disease virus - zoonosis from horses and other animals

Reverse Transcribing Viruses

Viruses that use their own reverse transcriptase enzymes for replication.

Group VI: ssRNA-RT Viruses

Group VI virus are single-stranded retroviruses that reverse transcribe a double-stranded DNA intermediate during genome replication.

family: Retroviridae - enveloped, capsid has icosahedral symmetry.
- genus: Deltaretrovirus
  - HTLV-1 - serotype of primate T-lymphotropic virus
  - HTLV-2 - serotype of primate T-lymphotropic virus
- genus: Lentivirus
  - HIV-1 - human immunodeficiency virus-1 (HIV/AIDS)
  - HIV-2 - human immunodeficiency virus-2 (HIV/AIDS)
- genus: Spumavirus
  - Human foamy virus - serotype of simian foamy virus