Viral 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]

Viral disease
Other names	Viral infection
Types of viral diseases
Specialty	Infectious disease
Causes	Virus
Medication	Antiviral drugs

Examples include the common cold, gastroenteritis, COVID-19, the flu, and rabies.^[2]

Structural characteristics

Virions of some of the most common human viruses with their relative size. Nucleic acids are not to scale. SARS stands for SARS-CoV-1 or COVID-19, variola viruses for smallpox.

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, Paramyxoviridae 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.

Pragmatic rules

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.^[3]
• One family of enveloped viruses causes gastroenteritis (Coronaviridae). All other viruses associated with gastroenteritis are non-enveloped.

Baltimore group

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 and species with characteristics

Family	Baltimore group	Important species	Envelopment
Adenoviridae	I[4][5]	Adenovirus[4][5]	N[4][5]
Herpesviridae	I[4][5]	Herpes simplex, type 1, Herpes simplex, type 2, Varicella-zoster virus, Epstein–Barr virus, Human cytomegalovirus, Human herpesvirus, type 8[6][7][8]	Y[4][5]
Papillomaviridae	I[4][9]	Human papillomavirus[4][9]	N[4][9]
Polyomaviridae	I[4][10]	BK virus, JC virus[4][10]	N[4][10]
Poxviridae	I[4][5]	Smallpox[4][5]	Y[4][5]
Parvoviridae	II[4][5]	Parvovirus B19[4][5]	N[4][5]
Reoviridae	III[11]	Rotavirus,[11] Orbivirus, Coltivirus, Banna virus	N[5]
Astroviridae	IV[12]	Human astrovirus[5]	N[5]
Caliciviridae	IV[11]	Norwalk virus[5]	N[5]
Coronaviridae	IV[13]	Human coronavirus 229E, Human coronavirus NL63, Human coronavirus OC43, Human coronavirus HKU1, Middle East respiratory syndrome-related coronavirus, Severe acute respiratory syndrome coronavirus,[5] Severe acute respiratory syndrome coronavirus 2	Y[5]
Flaviviridae	IV[4][5][14]	Hepatitis C virus,[4] yellow fever virus,[4] dengue virus,[4] West Nile virus,[4] TBE virus,[5] Zika virus	Y[4][5]
Hepeviridae	IV[15]	Hepatitis E virus[5]	N[5][15]
Matonaviridae	IV[4][5][16]	Rubella virus[4][17]	Y[4][5]
Picornaviridae	IV[18]	coxsackievirus, hepatitis A virus, poliovirus,[5] rhinovirus	N[5]
Arenaviridae	V[19]	Lassa virus[5][19]	Y[5][19]
Bunyaviridae	V[20]	Crimean-Congo hemorrhagic fever virus, Hantaan virus[5]	Y[5][20]
Filoviridae	V[21]	Ebola virus,[21] Marburg virus[21]	Y[5]
Orthomyxoviridae	V[4][22]	Influenza virus[4][22]	Y[4][22]
Paramyxoviridae	V[23]	Measles virus,[4] Mumps virus,[4] Parainfluenza virus[4][5]	Y[4][23]
Pneumoviridae	V [24]	Respiratory syncytial virus[4]	Y[4]
Rhabdoviridae	V[25]	Rabies virus[4][5]	Y[4][5]
Unassigned[26]	V[26]	Hepatitis D[26]	Y[26]
Retroviridae	VI[4][27]	HIV[4][5]	Y[4][5]
Hepadnaviridae	VII[4]	Hepatitis B virus[4][5]	Y[4][5]

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[4] fecal-oral[4] venereal[4] direct eye contact[4]	gastroenteritis[4] keratoconjunctivitis[4] pharyngitis[4] pharyngoconjunctival fever[4]	None[4]	Adenovirus vaccine hand washing covering mouth when coughing or sneezing avoiding close contact with the sick
Coxsackievirus	Picornaviridae	fecal-oral[4][28] respiratory[28] droplet contact[4]	Hand, foot and mouth disease[29] pleurodynia[28] aseptic meningitis[28] pericarditis myocarditis	None[4]	hand washing covering mouth when coughing/sneezing avoiding contaminated food/water improved sanitation
Cytomegalovirus	Herpesviridae	vertical transmission[4][30][31] bodily fluids[4]	infectious mononucleosis[4] Cytomegalic inclusion disease[4] Premature birth[31] liver, lung and spleen diseases in the newborn[31] Small size at birth[31] Small head size[31] congenital seizures in the newborn[31]	ganciclovir[4] cidofovir[4] foscarnet[4]	hand washing avoid sharing food and drinks with others safe sex
Epstein–Barr virus	Herpesviridae	saliva[4]	infectious mononucleosis[4] Burkitt's lymphoma[4] Hodgkin's lymphoma nasopharyngeal carcinoma	None[4]	avoiding close contact with the sick
Hepatitis A virus	Picornaviridae	fecal-oral[4][32]	acute hepatitis[4][32]	Immunoglobulin (post-exposure prophylaxis)[4]	Hepatitis A vaccine[4][32] avoiding contaminated food/water[4] improved sanitation
Hepatitis B virus	Hepadnaviridae	bodily fluids[4] Vertical and sexual[33]	acute hepatitis[4][33] chronic hepatitis[33] hepatic cirrhosis[33] hepatocellular carcinoma[33]	Lamivudine[4][33] immunoglobulin[4] Adefovir[4] Entecavir[4] Pegylated interferon alfa-2[4]	Hepatitis B vaccine[4][33] immunoglobulin (perinatal and post-exposure prophylaxis)[4] avoiding shared needles/syringes safe sex
Hepatitis C virus	Flaviviridae	blood[4] sexual contact[4]	acute hepatitis[4][34] chronic hepatitis[4] hepatic cirrhosis[4] hepatocellular carcinoma[4]	Ribavirin[4][34] Pegylated interferon alfa-2[4]	avoiding shared needles/syringes safe sex
Herpes simplex virus, type 1	Herpesviridae	direct contact[4][30] saliva[4][30]	herpes labialis,[4] cold sores[4][30] – can recur by latency[4] gingivostomatitis in children[4] tonsillitis & pharyngitis in adults[4] keratoconjunctivitis[4]	acyclovir[4][30] famciclovir[4][30] foscarnet[4] penciclovir[4]	avoiding close contact with lesions safe sex
Herpes simplex virus, type 2	Herpesviridae	sexual contact[4][30] vertical transmission[4][30]	Skin vesicles, mucosal ulcers,[30] Oral and/or genital[30] Can be latent[4] Aseptic meningitis[4]	acyclovir[4][30] famciclovir[4][30] foscarnet[4] penciclovir[4] cidofovir[4]	avoiding close contact with lesions[4] safe sex[4]
HIV	Retroviridae	sexual contact[4][35] blood[4][35] breast milk[4][35] vertical transmission	AIDS[4]	HAART,[4] such as protease inhibitors[35] and reverse-transcriptase inhibitors[35]	zidovudine (perinatally)[4] blood product screening[4] safe sex[4] 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[30] Sexual[30]	Kaposi sarcoma[4] multicentric Castleman disease[4] primary effusion lymphoma[4]	many in evaluation-stage[4]	avoid close contact with lesions safe sex
Human papillomavirus	Papillomaviridae	direct contact[4][36] sexual contact[36] vertical transmission	(common, flat, plantar and anogenital warts, laryngeal papillomas, epidermodysplasia verruciformis)[4] Malignancies for some species (cervical carcinoma,[36] squamous cell carcinomas)[4]	liquid nitrogen[4] laser vaporization[4] cytotoxic chemicals[4] interferon[4] cidofovir[4]	HPV vaccine[4][36] avoiding close contact with lesions[4] safe sex[4]
Influenza virus	Orthomyxoviridae	droplet contact[4]	influenza[4] (Reye syndrome)[4]	amantadine[4][22] rimantadine[4][22] zanamivir[4][22] oseltamivir[4][22]	influenza vaccine[4][22] amantadine[4] rimantadine[4] hand washing covering mouth when coughing/sneezing avoiding close contact with the sick
Measles virus	Paramyxoviridae	droplet contact[4][23]	measles[4][23] postinfectious encephalomyelitis[4]	None[4]	MMR vaccine[4][23] 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[4][23]	mumps[4][23]	None[4]	MMR vaccine[4][23] avoiding close contact with the sick
Parainfluenza virus	Paramyxoviridae	droplet contact[4][23]	croup[4] pneumonia[4] bronchiolitis[4] common cold[4]	None[4]	hand washing covering mouth when coughing/sneezing
Poliovirus	Picornaviridae	fecal-oral[4]	poliomyelitis[4]	None[4]	Polio vaccine[4][32] avoiding contaminated food and water improved sanitation
Rabies virus	Rhabdoviridae	animal bite[4][25] droplet contact[4]	rabies[4] (fatal encephalitis)[25]	Post-exposure prophylaxis[4]	rabies vaccine[25] avoiding rabid animals
Respiratory syncytial virus	Pneumoviridae	droplet contact[4][23] hand to mouth[4]	bronchiolitis[4] pneumonia[4] influenza-like syndrome[4] severe bronchiolitis with pneumonia[4]	(ribavirin)[4]	hand washing[4] avoiding close contact with the sick[4] palivizumab in high risk individuals[4] covering mouth when coughing/sneezing
Rubella virus	Togaviridae	Respiratory[37] droplet contact[4]	congenital rubella[4][37] German measles[4]	None[4]	MMR vaccine[4][37] 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)	Molnupiravir, Nirmatrelvir/ritonavir	hand washing covering mouth when coughing or sneezing social distancing
Varicella-zoster virus	Herpesviridae	droplet contact[4] direct contact	chickenpox[30] herpes zoster[4] Congenital varicella syndrome[30]	Varicella: acyclovir[4] famciclovir[4] valacyclovir[4] Zoster: acyclovir[4] famciclovir[4]	Varicella: varicella vaccine[4] varicella-zoster immunoglobulin[4] avoiding close contact with the sick Zoster: vaccine varicella-zoster immunoglobulin

See also

• List of latent human viral infections
• Pathogenic bacteria