Betaherpesvirinae is a subfamily of viruses in the order Herpesvirales, in the family Herpesviridae. Mammals serve as natural hosts. There are currently 18 species in this subfamily, divided among 4 genera. Diseases associated with this subfamily include: HHV-5: congenital CMV infection. HHV-6: 'sixth disease' (roseola infantum, exanthem subitum). HHV-7: symptoms analog to the 'sixth disease'.

Taxonomy

Group: dsDNA

Order: Herpesvirales

There are four known member species of the Betaherpesvirinae subfamily that are infectious for humans:

Human cytomegalovirus (HCMV), also known as human herpesvirus 5 (HHV-5),
Human herpesvirus 6A and 6B (HHV-6A and HHV-6B), which were classified as distinct species in 2012,
Human herpesvirus 7 (HHV-7)
Human cytomegalovirus (HCMV, HHV-5) "seems to have a large impact on immune parameters in later life and may contribute to increased morbidity and eventual mortality." Human herpesvirus 6A (HHV-6A) has been described as more neurovirulent, and as such is more frequently found in patients with neuroinflammatory diseases such as multiple sclerosis. Both human herpesvirus 6B (HHV-6B) and human herpesvirus 7 (HHV-7), as well as other viruses, can cause a skin condition in infants known as exanthema subitum, roseola infantum (rose rash of infants) or the sixth disease.

Structure

Viruses in Betaherpesvirinae are enveloped, with icosahedral, Spherical to pleomorphic, and Round geometries, and T=16 symmetry. The diameter is around 150-200 nm. Genomes are linear and non-segmented, around 140-240kb in length.

Genus Structure Symmetry Capsid Genomic Arrangement Genomic Segmentation
Roseolovirus Spherical Pleomorphic T=16 Enveloped Linear Monopartite
Cytomegalovirus Spherical Pleomorphic T=16 Enveloped Linear Monopartite
Proboscivirus Spherical Pleomorphic T=16 Enveloped Linear Monopartite
Muromegalovirus Spherical Pleomorphic T=16 Enveloped Linear Monopartite
Life Cycle

Viral replication is nuclear, and is lysogenic. Entry into the host cell is achieved by attachment of the viral glycoproteins to host receptors, which mediates endocytosis. Replication follows the dsDNA bidirectional replication model. DNA templated transcription, with some alternative splicing mechanism is the method of transcription. Translation takes place by leaky scanning. The virus exits the host cell by nuclear egress, and budding. Mammals serve as the natural host. Transmission routes are transplancental, transplantation, blood transfusion, body fluids, urine, and saliva.

Betaherpesvirinae establish latency (site where virus lies dormant until reactivated) in leukocytes. This is different from Alphaherpesvirinae, which establish latency in neurons, and Gammaherpesvirinae, which establish latency in cells of the immune system, such as B-cells.

Genus Host Details Tissue Tropism Entry Details Release Details Replication Site Assembly Site Transmission
Roseolovirus Humans T-cells; B-cells; NK-cell; monocytes; macrophages; epithelial Glycoprotiens Budding Nucleus Nucleus Respiratory contact
Cytomegalovirus Humans; monkeys Epithelial mucosa Glycoprotiens Budding Nucleus Nucleus Urine; saliva
Proboscivirus Elephants None Glycoprotiens Budding Nucleus Nucleus Contact
Muromegalovirus Rodents Salivary glands Glycoprotiens Budding Nucleus Nucleus Contact

source - Wikipedia