Viral disease

Viral disease
Classification and external resources
MeSH	D014777

A viral disease (or viral infection) 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.

Useful rules of thumb

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 almost 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	droplet contact[3][9] fecal-oral[3][9] venereal[3] direct eye contact[3]	gastroenteritis[3][9] keratoconjunctivitis[3][9] pharyngitis[3] croup[9] pharyngoconjunctival fever[3] pneumonia[9] pneumonia[9] cystitis[9]	None[3][9]	Adenovirus vaccine[9] hand washing covering mouth when coughing or sneezing avoiding close contact with the sick
Coxsackievirus	Picornaviridae	fecal-oral[3][26] respiratory[26] droplet contact[3]	Hand, foot and mouth disease[27] pleurodynia[26] aseptic meningitis[26] pericarditis myocarditis	None[3]	hand washing covering mouth when coughing/sneezing avoiding contaminated food/water improved sanitation
Epstein–Barr virus	Herpesviridae	saliva[3]	infectious mononucleosis[3] Burkitt's lymphoma[3] Hodgkin's lymphoma nasopharyngeal carcinoma	None[3]	avoiding close contact with the sick
Hepatitis A virus	Picornaviridae	fecal-oral[3][28]	acute hepatitis[3][28]	Immunoglobulin (post-exposure prophylaxis)[3]	Hepatitis A vaccine[3][28] avoiding contaminated food/water[3] improved sanitation
Hepatitis B virus	Hepadnaviridae	bodily fluids[3] Vertical and sexual[29]	acute hepatitis[3][29] chronic hepatitis[29] hepatic cirrhosis[29] hepatocellular carcinoma[29]	Lamivudine[3][29] immunoglobulin[3] Adefovir[3] Entecavir[3] Pegylated interferon alfa-2[3]	Hepatitis B vaccine[3][29] immunoglobulin (perinatal and post-exposure prophylaxis)[3] avoiding shared needles/syringes safe sex
Hepatitis C virus	Flaviviridae	blood[3] sexual contact[3]	acute hepatitis[3][30] chronic hepatitis[3] hepatic cirrhosis[3] hepatocellular carcinoma[3]	Ribavirin[3][30] Pegylated interferon alfa-2[3]	avoiding shared needles/syringes safe sex
Herpes simplex virus, type 1	Herpesviridae	direct contact[3][31] saliva[3][31]	herpes labialis,[3] cold sores[3][31] - can recur by latency[3] gingivostomatitis in children[3] tonsillitis & pharyngitis in adults[3] keratoconjunctivitis[3]	acyclovir[3][31] famciclovir[3][31] foscarnet[3] penciclovir[3]	avoiding close contact with lesions safe sex
Herpes simplex virus, type 2	Herpesviridae	sexual contact[3][31] vertical transmission[3][31]	Skin vesicles, mucosal ulcers,[31] Oral and/or genital[31] Can be latent[3] Aseptic meningitis[3]	acyclovir[3][31] famciclovir[3][31] foscarnet[3] penciclovir[3] cidofovir[3]	avoiding close contact with lesions[3] safe sex[3]
Cytomegalovirus	Herpesviridae	vertical transmission[3][31] bodily fluids[3]	infectious mononucleosis[3] Cytomegalic inclusion disease[3]	ganciclovir[3] cidofovir[3] foscarnet[3]	hand washing avoid sharing food and drinks with others safe sex
Human herpesvirus, type 8	Herpesviridae	Saliva[31] Sexual[31]	Kaposi sarcoma[3] multicentric Castleman disease[3] primary effusion lymphoma[3]	many in evaluation-stage[3]	avoid close contact with lesions safe sex
HIV	Retroviridae	sexual contact[3][32] blood[3][32] breast milk[3][32] vertical transmission	AIDS[3]	HAART,[3] such as protease inhibitors[32] and reverse-transcriptase inhibitors[32]	zidovudine (perinatally)[3] blood product screening[3] safe sex[3] avoiding shared needles/syringes
Influenza virus	Orthomyxoviridae	droplet contact[3]	influenza[3] (Reye syndrome)[3]	amantadine[3][19] rimantadine[3][19] zanamivir[3][19] oseltamivir[3][19]	influenza vaccine[3][19] amantadine[3] rimantadine[3] hand washing covering mouth when coughing/sneezing avoiding close contact with the sick
Measles virus	Paramyxoviridae	droplet contact[3][23]	measles[3][23] postinfectious encephalomyelitis[3]	None[3]	MMR vaccine[3][23] quarantining the sick avoiding contact with the sick
Mumps virus	Paramyxoviridae	droplet contact[3][23]	mumps[3][23]	None[3]	MMR vaccine[3][23] avoiding close contact with the sick
Human papillomavirus	Papillomaviridae	direct contact[3][33] sexual contact[33] vertical transmission	hyperplastic epithelial lesions (common, flat, plantar and anogenital warts, laryngeal papillomas, epidermodysplasia verruciformis)[3] Malignancies for some species (cervical carcinoma,[33] squamous cell carcinomas)[3]	liquid nitrogen[3] laser vaporization[3] cytotoxic chemicals[3] interferon[3] cidofovir[3]	HPV vaccine[3][33] avoiding close contact with lesions[3] safe sex[3]
Parainfluenza virus	Paramyxoviridae	droplet contact[3][23]	croup[3] pneumonia[3] bronchiolitis[3] common cold[3]	None[3]	hand washing covering mouth when coughing/sneezing
Poliovirus	Picornaviridae	fecal-oral[3]	poliomyelitis[3]	None[3]	Polio vaccine[3][28] avoiding contaminated food and water improved sanitation
Rabies virus	Rhabdoviridae	animal bite[3][24] droplet contact[3]	rabies[3] (fatal encephalitis)[24]	Post-exposure prophylaxis[3]	rabies vaccine[24] avoiding rabid animals
Respiratory syncytial virus	Paramyxoviridae	droplet contact[3][23] hand to mouth[3]	bronchiolitis[3] pneumonia[3] influenza-like syndrome[3] severe bronchiolitis with pneumonia[3]	(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	Respiratory[34] droplet contact[3]	congenital rubella[3][34] German measles[3]	None[3]	MMR vaccine[3][34] avoiding close contact with the sick
Varicella-zoster virus	Herpesviridae	droplet contact[3] direct contact	chickenpox[31] herpes zoster[3] Congenital varicella syndrome[31]	Varicella: acyclovir[3] famciclovir[3] valacyclovir[3] Zoster: acyclovir[3] famciclovir[3]	Varicella: varicella vaccine[3] varicella-zoster immunoglobulin[3] avoiding close contact with the sick Zoster: vaccine varicella-zoster immunoglobulin

Notes

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.^[35] 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.^[36]

See also

• Folding@home
• List of latent human viral infections
• Pathogenic bacteria

References

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19. "Orthomyxoviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-03.
20. "Arenaviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-03.
21. "Bunyaviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-03.
22. "Filoviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-03.
23. "Paramyxoviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-10.
24. "Rhabdoviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-03.
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29. "Hepadnaviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-10.
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31. "Herpesviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-10.
32. "Human immunodeficiency virus 1". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-10.
33. "Papillomaviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-10.
34. "Togaviridae". ViralZone. SIB Swiss Institute of Bioinformatics. Retrieved 2015-10-10.
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