Viral Disease

Viral disease
Other names: viral infection
Transmission electron micrograph of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virions
Specialty	Infectious disease

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]

Structure[edit | edit source]

Basic structural characteristics, such as genome type, virion shape and replication site, generally share the same features among virus species within the same family.^{[citation needed]}

• 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.
• Partly double-stranded DNA viruses: Hepadnaviridae. These viruses are enveloped.
• One family of single-stranded DNA viruses infects humans: Parvoviridae. These viruses are non-enveloped.
• Positive single-stranded RNA families: three non-enveloped (Astroviridae, Caliciviridae and Picornaviridae) and four enveloped (Coronaviridae, Flaviviridae, Retroviridae and Togaviridae). All the non-enveloped families have icosahedral nucleocapsids.
• Negative single-stranded RNA families: Arenaviridae, Bunyaviridae, Filoviridae, Orthomyxoviridae, ParamyxoviridaeParamyxoviridae and Rhabdoviridae. All are enveloped with helical nucleocapsids.
• Double-stranded RNA genome: Reoviridae.
• The Hepatitis D virus has not yet been assigned to a family, but is clearly distinct from the other families infecting humans.
• 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.

• 

  Virions of some of the most common human viruses with their relative size. Nucleic acids are not to scale. SARS stands as for SARS as for COVID-19, variola viruses for smallpox.

• 

  Immunohistochemical staining of liver biopsy specimen, strong cytoplasmic staining for hepatitis A virus antigen was noted

Viral families[edit | edit source]

Human-infecting virus families offer rules that may assist physicians and medical microbiologists/virologists.^{[citation needed]}

As a general rule, DNA viruses replicate within the cell 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.^{[citation needed]}

• Segmented genomes: Bunyaviridae, Orthomyxoviridae, Arenaviridae, and Reoviridae (acronym BOAR). All are RNA viruses.
• Viruses transmitted almost exclusively by arthropods: Bunyavirus, Flavivirus, and Togavirus. Some Reoviruses are transmitted from arthropod vectors. All are RNA viruses.^[2]
• One family of enveloped viruses causes gastroenteritis (Coronaviridae). All other viruses associated with gastroenteritis are non-enveloped.

Baltimore Group[edit | edit source]

This group of analysts defined multiple categories of virus. Groups:^{[citation needed]}

• I - dsDNA
• II - ssDNA
• III - dsRNA
• IV - positive-sense ssRNA
• V - negative-sense ssRNA
• VI - ssRNA-RT
• VII - dsDNA-RT

Clinically important virus families[edit | edit source]

Clinically important virus families and species with characteristics

Family	Baltimore group	Important species	Envelopment
Adenoviridae	I[3][4]	Adenovirus[3][4]	N[3][4]
Herpesviridae	I[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]	Y[3][4]
Papillomaviridae	I[3][8]	Human papillomavirus[3][8]	N[3][8]
Polyomaviridae	I[3][9]	BK virus, JC virus[3][9]	N[3][9]
Poxviridae	I[3][4]	Smallpox[3][4]	Y[3][4]
Parvoviridae	II[3][4]	Parvovirus B19[3][4]	N[3][4]
Reoviridae	III[10]	Rotavirus,[10] Orbivirus, Coltivirus, Banna virus	N[4]
Astroviridae	IV[11]	Human astrovirus[4]	N[4]
Caliciviridae	IV[10]	Norwalk virus[4]	N[4]
Coronaviridae	IV[12]	Human coronavirus 229E, Human coronavirus NL63, Human coronavirus OC43, Human coronavirus HKU1, Middle East respiratory syndrome-related coronavirus, Severe acute respiratory syndrome coronavirus,[4] Severe acute respiratory syndrome coronavirus 2	Y[4]
Flaviviridae	IV[3][4][13]	Hepatitis C virus,[3] yellow fever virus,[3] dengue virus,[3] West Nile virus,[3] TBE virus,[4] Zika virus	Y[3][4]
Hepeviridae	IV[14]	Hepatitis E virus[4]	N[4][14]
Matonaviridae	IV[3][4][15]	Rubella virus[3][16]	Y[3][4]
Picornaviridae	IV[17]	coxsackievirus, hepatitis A virus, poliovirus,[4] rhinovirus	N[4]
Arenaviridae	V[18]	Lassa virus[4][18]	Y[4][18]
Bunyaviridae	V[19]	Crimean-Congo hemorrhagic fever virus, Hantaan virus[4]	Y[4][19]
Filoviridae	V[20]	Ebola virus,[20] Marburg virus[20]	Y[4]
Orthomyxoviridae	V[3][21]	Influenza virus[3][21]	Y[3][21]
Paramyxoviridae	V[22]	Measles virus,[3] Mumps virus,[3] Parainfluenza virus[3][4]	Y[3][22]
Pneumoviridae	V [23]	Respiratory syncytial virus[3]	Y[3]
Rhabdoviridae	V[24]	Rabies virus[3][4]	Y[3][4]
Unassigned[25]	V[25]	Hepatitis D[25]	Y[25]
Retroviridae	VI[3][26]	HIV[3][4]	Y[3][4]
Hepadnaviridae	VII[3]	Hepatitis B virus[3][4]	Y[3][4]

Clinical characteristics[edit | edit source]

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] fecal-oral[3] venereal[3] direct eye contact[3]	gastroenteritis[3] keratoconjunctivitis[3] pharyngitis[3] pharyngoconjunctival fever[3]	None[3]	Adenovirus vaccine hand washing covering mouth when coughing or sneezing avoiding close contact with the sick
Coxsackievirus	Picornaviridae	fecal-oral[3][27] respiratory[27] droplet contact[3]	Hand, foot and mouth disease[28] pleurodynia[27] aseptic meningitis[27] pericarditis myocarditis	None[3]	hand washing covering mouth when coughing/sneezing avoiding contaminated food/water improved sanitation
Cytomegalovirus	Herpesviridae	vertical transmission[3][29][30] bodily fluids[3]	infectious mononucleosis[3] Cytomegalic inclusion disease[3] Premature birth[30] liver, lung and spleen diseases in the newborn[30] Small size at birth[30] Small head size[30] congenital seizures in the newborn[30]	ganciclovir[3] cidofovir[3] foscarnet[3]	hand washing avoid sharing food and drinks with others safe sex
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][31]	acute hepatitis[3][31]	Immunoglobulin (post-exposure prophylaxis)[3]	Hepatitis A vaccine[3][31] avoiding contaminated food/water[3] improved sanitation
Hepatitis B virus	Hepadnaviridae	bodily fluids[3] Vertical and sexual[32]	acute hepatitis[3][32] chronic hepatitis[32] hepatic cirrhosis[32] hepatocellular carcinoma[32]	Lamivudine[3][32] immunoglobulin[3] Adefovir[3] Entecavir[3] Pegylated interferon alfa-2[3]	Hepatitis B vaccine[3][32] 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][33] chronic hepatitis[3] hepatic cirrhosis[3] hepatocellular carcinoma[3]	Ribavirin[3][33] Pegylated interferon alfa-2[3]	avoiding shared needles/syringes safe sex
Herpes simplex virus, type 1	Herpesviridae	direct contact[3][29] saliva[3][29]	herpes labialis,[3] cold sores[3][29] – can recur by latency[3] gingivostomatitis in children[3] tonsillitis & pharyngitis in adults[3] keratoconjunctivitis[3]	acyclovir[3][29] famciclovir[3][29] foscarnet[3] penciclovir[3]	avoiding close contact with lesions safe sex
Herpes simplex virus, type 2	Herpesviridae	sexual contact[3][29] vertical transmission[3][29]	Skin vesicles, mucosal ulcers,[29] Oral and/or genital[29] Can be latent[3] Aseptic meningitis[3]	acyclovir[3][29] famciclovir[3][29] foscarnet[3] penciclovir[3] cidofovir[3]	avoiding close contact with lesions[3] safe sex[3]
HIV	Retroviridae	sexual contact[3][34] blood[3][34] breast milk[3][34] vertical transmission	AIDS[3]	HAART,[3] such as protease inhibitors[34] and reverse-transcriptase inhibitors[34]	zidovudine (perinatally)[3] blood product screening[3] safe sex[3] avoiding shared needles/syringes
Human coronavirus 229E (HCoV-229E)	Coronaviridae	droplet contact fomites	common cold pneumonia bronchiolitis
Human coronavirus NL63 (HCoV-NL63)	Coronaviridae	droplet contact	common cold rhinitis bronchitis bronchiolitis pneumonia croup
Human coronavirus OC43 (HCoV-OC43)	Coronaviridae		common cold pneumonia
Human coronavirus HKU1 (HCoV-HKU1)	Coronaviridae		common cold pneumonia bronchiolitis
Human herpesvirus, type 8	Herpesviridae	Saliva[29] Sexual[29]	Kaposi sarcoma[3] multicentric Castleman disease[3] primary effusion lymphoma[3]	many in evaluation-stage[3]	avoid close contact with lesions safe sex
Human papillomavirus	Papillomaviridae	direct contact[3][35] sexual contact[35] vertical transmission	(common, flat, plantar and anogenital warts, laryngeal papillomas, epidermodysplasia verruciformis)[3] Malignancies for some species (cervical carcinoma,[35] squamous cell carcinomas)[3]	liquid nitrogen[3] laser vaporization[3] cytotoxic chemicals[3] interferon[3] cidofovir[3]	HPV vaccine[3][35] avoiding close contact with lesions[3] safe sex[3]
Influenza virus	Orthomyxoviridae	droplet contact[3]	influenza[3] (Reye syndrome)[3]	amantadine[3][21] rimantadine[3][21] zanamivir[3][21] oseltamivir[3][21]	influenza vaccine[3][21] amantadine[3] rimantadine[3] hand washing covering mouth when coughing/sneezing avoiding close contact with the sick
Measles virus	Paramyxoviridae	droplet contact[3][22]	measles[3][22] postinfectious encephalomyelitis[3]	None[3]	MMR vaccine[3][22] quarantining the sick avoiding contact with the sick
Middle East respiratory syndrome-related coronavirus (MERS-CoV)	Coronaviridae	close human contact	Middle East respiratory syndrome (MERS)
Mumps virus	Paramyxoviridae	droplet contact[3][22]	mumps[3][22]	None[3]	MMR vaccine[3][22] avoiding close contact with the sick
Parainfluenza virus	Paramyxoviridae	droplet contact[3][22]	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][31] 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	Pneumoviridae	droplet contact[3][22] 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[36] droplet contact[3]	congenital rubella[3][36] German measles[3]	None[3]	MMR vaccine[3][36] avoiding close contact with the sick
Severe acute respiratory syndrome coronavirus (SARS-CoV)	Coronaviridae	droplet contact	severe acute respiratory syndrome (SARS)
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)	Coronaviridae	droplet contact	coronavirus disease 2019 (COVID-19)		hand washing covering mouth when coughing or sneezing social distancing
Varicella-zoster virus	Herpesviridae	droplet contact[3] direct contact	chickenpox[29] herpes zoster[3] Congenital varicella syndrome[29]	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

See also[edit | edit source]

• List of latent human viral infections
• Pathogenic bacteria

References[edit | edit source]

External links[edit | edit source]

Classification	MeSH: D014777