A viral disease, or viral infection, occurs when an organism’s body is invaded by pathogenic viruses.

The infectious virus particles, virions, attach to and enter susceptible cells.

Virus species within the same family generally share the same features:

Basic structural characteristics, such as genome type, virion shape and replication site.

Double-stranded DNA families: three are non-enveloped: Adenoviridae, Papillomaviridae and Polyomaviridae, and two are enveloped:Herpesviridae and Poxviridae.

All non-enveloped families have icosahedral nucleotide capsids.

Partly double-stranded DNA viruses: Hepadnaviridae :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.

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 infect humans and not be associated with disease: that have Anelloviridae and the genus Dependovirus are non-enveloped single-stranded DNA viruses.

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

Bunyaviridae, Orthomyxoviridae, Arenaviridae, and Reoviridae are all RNA viruses.

The Viruses transmitted almost exclusively by arthropods: Bunyavirus, Flavivirus, and Togavirus.

Some Reoviruses are transmitted from arthropod vectors, and al all are RNA viruses.

One family of enveloped viruses causes gastroenteritis-Coronaviridae.

All other viruses associated with gastroenteritis are non-enveloped.

Categories of virus by groups:

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

Adenoviridae=Adenovirus

Herpesviridae I-Herpes simplex, type 1, Herpes simplex, type 2, Varicella-zoster virus, Epstein–Barr virus, Human cytomegalovirus, Human herpesvirus, type 8

Papillomaviridae Human papillomavirus

Polyomaviridae-BK virus, JC virus N

Poxviridae Smallpox, Monkey pox

Parvoviridae-Parvovirus B19

ReoviridaeIII-Rotavirus, Orbivirus, Coltivirus, Banna virus

AstroviridaeIV-Human astrovirus

Caliciviridae IV Norwalk virus

Coronaviridae IV-Human coronavirus 229E, Human coronavirus NL63, Human coronavirus OC43, Human coronavirus HKU1, Middle East respiratory syndrome-related coronavirus, Severe acute respiratory syndrome coronavirus,Severe acute respiratory syndrome coronavirus 2, COVID-19

Flaviviridae IV-Hepatitis C virus, yellow fever virus, dengue virus,[West Nile virus, TBE virus, Zika virus

Hepeviridae IV Hepatitis E virus

Matonaviridae IV Rubella virus

Picornaviridae IV-coxsackievirus, hepatitis A virus, poliovirus,rhinovirus

Arenaviridae V Lassa virus

Bunyaviridae V Crimean-Congo hemorrhagic fever virus, Hantaan virus

FiloviridaeV Ebola virus,Marburg virus

Orthomyxoviridae V Influenza virus

ParamyxoviridaeV Measles virus, Mumps virus,Parainfluenza virus

PneumoviridaeV Respiratory syncytial virus

RhabdoviridaeV Rabies virus

Unassigned V Hepatitis D

Retroviridae VI HIV

Hepadnaviridae VII Hepatitis B virus

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

Reactivation of latent viruses common cause of infections in hematopoietic stem cell transplant patients, such as herpes simplex virus types 1 and 2, vermicelli zoster virus and cytomegalovirus.

Viroporins are small, highly hydrophobic proteins derived from viruses, which interact with membranes to modify the host cell’s permeability to ions or other small molecules.

Several viroporins are observed to localize to the Golgi apparatus and other cytoplasmic structures during viral infection.

CMV infections common among the most common viral infections in the immunocompromised host.

Viruses infect living cells and co-opt the host replication process to produce viral progeny that infects other cells.

For viruses to thrive they must overcome the regulatory components of the cell cycle and avoid a apptosis and the hosts immune surveillance.

Chronic infections are associated with the development of several types of cancer.

Virus- associated malignant tumors account for 10 to 15% of all human cancers worldwide.