Viral Infection
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Viral Infection

A viral disease (or viral infection or infectious disease), occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells.[1]

Structural characteristics

Basic structural characteristics, such as genome type, virion shape and replication site, generally share the same features among virus species within the same family.

There are five double-stranded DNA families: three are non enveloped (Adenoviridae, Papillomaviridae and Polyomaviridae) and two are enveloped (Herpesviridae and Poxviridae). All of the non-enveloped families have icosahedral capsids.

There is one family of partly double-stranded DNA viruses: Hepadnaviridae. These viruses are enveloped.

There is one family of single-stranded DNA viruses that infect humans: Parvoviridae. These viruses are non-enveloped.

There are seven positive single-stranded RNA families: three non enveloped (Astroviridae, Caliciviridae and Picornaviridae) and four enveloped (Coronoviridae, Flaviviridae, Retroviridae and Togaviridae). All the non-enveloped families have icosahedral nucleocapsids.

There are six negative single-stranded RNA families: Arenaviridae, Bunyaviridae, Filoviridae, Orthomyxoviridae, Paramyxoviridae and Rhabdoviridae. All are enveloped with helical nucleocapsids.

There is one family with a double-stranded RNA genome: Reoviridae.

There is one additional virus (Hepatitis D virus) which has not yet been assigned to a family but is clearly distinct from the other families infecting humans.

There is one family and one genus of viruses known to infect humans that have not been associated with disease: the family Anelloviridae and the genus Dependovirus. Both of these taxa are non-enveloped single-stranded DNA viruses.

Pragmatic rules

Among the human infecting families there are a number of rules that may assist physicians and medical microbiologists/virologists.

As a general rule, DNA viruses replicate within the nucleus while RNA viruses replicate within the cytoplasm. Exceptions are known to this rule: poxviruses replicate within the cytoplasm and orthomyxoviruses and hepatitis D virus (RNA viruses) replicate within the nucleus.

Four families have segmented genomes: Bunyaviridae, Orthomyxoviridae, Arenaviridae and Reoviridae (acronym BOAR). All are RNA viruses.

Three families are transmitted almost exclusively by arthropods: Bunyavirus, Flavivirus and Togavirus. Some Reoviruses are transmitted from arthropod vectors as well. All are RNA viruses.[2]

Only one family of enveloped viruses causes gastroenteritis (Coronaviridae). All other viruses associated with gastroenteritis are non enveloped.

These are tables of the clinically most important[3] viruses.

Comparison table of clinically important virus families and species
Family Baltimore group Important species envelopment
Adenoviridae Group I (dsDNA)[3][4] Adenovirus[3][4] non-enveloped[3][4]
Herpesviridae Group I (dsDNA)[3][4] Herpes simplex, type 1, Herpes simplex, type 2, Varicella-zoster virus, Epstein-Barr virus, Human cytomegalovirus, Human herpesvirus, type 8[5][6][7] enveloped[3][4]
Papillomaviridae Group I (dsDNA)[3][8] Human papillomavirus[3][8] non-enveloped[3][8]
Polyomaviridae Group I (dsDNA)[3][9] BK virus, JC virus[3][9] non-enveloped[3][9]
Poxviridae Group I (dsDNA)[3][4] Smallpox[3][4] enveloped[3][4]
Hepadnaviridae Group VII (dsDNA-RT)[3][10] Hepatitis B virus[3][4] enveloped[3][4]
Parvoviridae Group II (ssDNA)[3][4] Parvovirus B19[3][4] non-enveloped[3][4]
Astroviridae Group IV (positive-sense ssRNA)[11] Human astrovirus[4] non-enveloped[4]
Caliciviridae Group IV (positive-sense ssRNA)[12] Norwalk virus[4] non-enveloped[4]
Picornaviridae Group IV (positive-sense ssRNA)[13] coxsackievirus, hepatitis A virus, poliovirus,[4]rhinovirus non-enveloped[4]
Coronaviridae Group IV (positive-sense ssRNA)[14] Severe acute respiratory syndrome virus[4] enveloped[4]
Flaviviridae Group IV (positive-sense ssRNA)[3][4][15] Hepatitis C virus,[3]yellow fever virus,[3]dengue virus,[3]West Nile virus,[3]TBE virus[4] enveloped[3][4]
Togaviridae Group IV (positive-sense ssRNA)[3][4][16] Rubella virus[3] enveloped[3][4]
Hepeviridae Group IV (positive-sense ssRNA)[17] Hepatitis E virus[4] non-enveloped[4][17]
Retroviridae Group VI (ssRNA-RT)[3][18] Human immunodeficiency virus (HIV)[3][4] enveloped[3][4]
Orthomyxoviridae Group V (negative-sense ssRNA)[3][19] Influenza virus[3][19] enveloped[3][19]
Arenaviridae Group V (negative-sense ssRNA)[20] Lassa virus[4][20] enveloped[4][20]
Bunyaviridae Group V (negative-sense ssRNA)[21] Crimean-Congo hemorrhagic fever virus, Hantaan virus[4] enveloped[4][21]
Filoviridae Group V (negative-sense ssRNA)[22] Ebola virus,[22]Marburg virus[22] enveloped[4]
Paramyxoviridae Group V (negative-sense ssRNA)[23] Measles virus,[3]Mumps virus,[3]Parainfluenza virus,[3]Respiratory syncytial virus,[3][4] enveloped[3][23]
Rhabdoviridae Group V (negative-sense ssRNA)[24] Rabies virus[3][4] enveloped[3][4]
Unassigned[25] Group V (negative-sense ssRNA)[25] Hepatitis D[25] enveloped[25]
Reoviridae Group III (dsRNA)[12] Rotavirus,[12]Orbivirus, Coltivirus, Banna virus non-enveloped[4]

Clinical characteristics

The clinical characteristics of viruses may differ substantially among species within the same family:

Type Family Transmission Diseases Treatment Prevention
Adenovirus Adenoviridae None[3][9]
  • Adenovirus vaccine[9]
  • hand washing
  • covering mouth when coughing or sneezing
  • avoiding close contact with the sick
Coxsackievirus Picornaviridae None[3]
  • hand washing
  • covering mouth when coughing/sneezing
  • avoiding contaminated food/water
  • improved sanitation
Epstein-Barr virus Herpesviridae None[3]
  • avoiding close contact with the sick
Hepatitis A virus Picornaviridae Immunoglobulin (post-exposure prophylaxis)[3]
Hepatitis B virus Hepadnaviridae

Vertical and sexual[29]

Hepatitis C virus Flaviviridae
  • avoiding shared needles/syringes
  • safe sex
Herpes simplex virus, type 1 Herpesviridae
  • avoiding close contact with lesions
  • safe sex
Herpes simplex virus, type 2 Herpesviridae
  • avoiding close contact with lesions[3]
  • safe sex[3]
Cytomegalovirus Herpesviridae
  • hand washing
  • avoid sharing food and drinks with others
  • safe sex
Human herpesvirus, type 8 Herpesviridae many in evaluation-stage[3]
  • avoid close contact with lesions
  • safe sex
HIV Retroviridae HAART,[3] such as protease inhibitors[33] and reverse-transcriptase inhibitors[33]
  • zidovudine (perinatally)[3]
  • blood product screening[3]
  • safe sex[3]
  • avoiding shared needles/syringes
Influenza virus Orthomyxoviridae
  • droplet contact[3]
Measles virus Paramyxoviridae None[3]
Mumps virus Paramyxoviridae None[3]
Human papillomavirus Papillomaviridae
Parainfluenza virus Paramyxoviridae None[3]
  • hand washing
  • covering mouth when coughing/sneezing
Poliovirus Picornaviridae None[3]
Rabies virus Rhabdoviridae Post-exposure prophylaxis[3]
Respiratory syncytial virus Paramyxoviridae (ribavirin)[3]
  • hand washing[3]
  • avoiding close contact with the sick[3]
  • palivizumab in high risk individuals[3]
  • covering mouth when coughing/sneezing
Rubella virus Togaviridae None[3]
Varicella-zoster virus Herpesviridae
  • droplet contact[3]
  • direct contact





  • vaccine
  • varicella-zoster immunoglobulin


In 2010 it was reported that the presence of a tobamovirus (Pepper mild mottle virus) in the stool was associated with clinical disease and a specific immune response.[36] If this association can be confirmed it is the first known case of disease caused by a virus previously considered pathogenic only to plants.

Diagnosis and treatment

Viral disease is usually detected by clinical presentation, for instance severe muscle and joint pains preceding fever, or skin rash and swollen lymph glands. Laboratory investigation is not directly effective in detecting viral infections, because they do not themselves increase the white blood cell count. Laboratory investigation may be useful in diagnosing associated bacterial infections, however. Viral infections are commonly of limited duration, so treatment usually consists in reducing the symptoms; antipyretic and analgesic drugs are commonly prescribed.[37]

See also


  1. ^ Taylor, M.P.; Kobiler, O.; Enquist, L. W. (2012). "Alphaherpesvirus axon-to-cell spread involves limited virion transmission". Proceedings of the National Academy of Sciences. PNAS. 106: 17046-17051. doi:10.1073/pnas.1212926109. PMC 3479527.
  2. ^ Hunt, M. "Arboviruses". University of South Carolina School of Medicine.
  3. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew ex ey ez fa fb fc fd fe ff fg fh fi fj fk fl fm fn fo fp fq fr fs ft fu fv fw fx fy fz ga gb gc gd ge gf gg gh gi Fisher, Bruce; Harvey, Richard P.; Champe, Pamela C. (2007). Lippincott's Illustrated Reviews: Microbiology. Lippincott's Illustrated Reviews Series. Hagerstown MD: Lippincott Williams & Wilkins. pp. 354-366. ISBN 0-7817-8215-5.
  4. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am Table 1 in: Dimitrov, Dimiter S. (2004). "Virus entry: molecular mechanisms and biomedical applications". Nature Reviews Microbiology. 2 (2): 109-122. doi:10.1038/nrmicro817. ISSN 1740-1526.
  5. ^ Adams, MJ; Carstens EB (Jul 2012). "Ratification vote on taxonomic proposals to the International Committee on Taxonomy of Viruses (2012)" (PDF). Arch. Virol. 157 (7): 1411-22. doi:10.1007/s00705-012-1299-6. PMID 22481600.
  6. ^ Whitley RJ (1996). Baron S; et al. (eds.). Herpesviruses. in: Baron's Medical Microbiology (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.
  7. ^ Murray PR, Rosenthal KS, Pfaller MA (2005). Medical Microbiology (5th ed.). Elsevier Mosby. ISBN 978-0-323-03303-9.
  8. ^ a b c de Villiers EM, Fauquet C, Broker TR, Bernard HU, zur Hausen H (2004). "Classification of papillomaviruses". Virology. 324 (1): 17-27. doi:10.1016/j.virol.2004.03.033. PMID 15183049.
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  10. ^ Blaine T. Smith; Brian Luke Seaward. Pharmacology for Nurses. Jones & Bartlett Publishers=year=2014. ISBN 9781449689407.
  11. ^ Murillo A, Vera-Estrella R, Barkla BJ, Méndez E, Arias CF (2015). "Identification of Host Cell Factors Associated with Astrovirus Replication in Caco-2 Cells". J. Virol. 89 (20): 10359-70. doi:10.1128/JVI.01225-15. PMC 4580174. PMID 26246569.
  12. ^ a b c Page 273 in: Lennette's Laboratory Diagnosis of Viral Infections (Fourth ed.). CRC Press. 2010. ISBN 9781420084962.
  13. ^ Tuthill, Tobias J.; Groppelli, Elisabetta; Hogle, James M.; Rowlands, David J. (2010). "Picornaviruses". Current Topics in Microbiology and Immunology. 343: 43-89. doi:10.1007/82_2010_37. ISSN 0070-217X. PMC 3018333.
  14. ^ Stapleford, Kenneth A.; Miller, David J. (2010). "Role of Cellular Lipids in Positive-Sense RNA Virus Replication Complex Assembly and Function". Viruses. 2 (5): 1055-1068. doi:10.3390/v2051055. ISSN 1999-4915. PMC 3187604.
  15. ^ Cook, S.; Moureau, G.; Harbach, R. E.; Mukwaya, L.; Goodger, K.; Ssenfuka, F.; Gould, E.; Holmes, E. C.; de Lamballerie, X. (2009). "Isolation of a novel species of flavivirus and a new strain of Culex flavivirus (Flaviviridae) from a natural mosquito population in Uganda". Journal of General Virology. 90 (11): 2669-2678. doi:10.1099/vir.0.014183-0. ISSN 0022-1317. PMC 2885038.
  16. ^ Simon-Loriere, Etienne; Holmes, Edward C. (2011). "Why do RNA viruses recombine?". Nature Reviews Microbiology. 9 (8): 617-626. doi:10.1038/nrmicro2614. ISSN 1740-1526. PMC 3324781. PMID 21725337.
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  18. ^ "Retroviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved .
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  32. ^ a b c d e f "Babies Born with CMV (Congenital CMV Infection)". Centers for Disease Control and Prevention. April 13, 2017. Retrieved 2017. This article incorporates public domain material from websites or documents of the Centers for Disease Control and Prevention.
  33. ^ a b c d e "Human immunodeficiency virus 1". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved .
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  37. ^ "Viral Fever". Web Health Centre. Retrieved 2013.

External links


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