Viral envelope

Schematic of a Cytomegalovirus

Some viruses (e.g. influenza and many animal viruses) have viral envelopes covering their protective protein capsids.^[1] The envelopes are typically derived from portions of the host cell membranes (phospholipids and proteins), but include some viral glycoproteins. They may help viruses avoid the host immune system. Glycoproteins on the surface of the envelope serve to identify and bind to receptor sites on the host's membrane. The viral envelope then fuses with the host's membrane, allowing the capsid and viral genome to enter and infect the host.

The cell from which the virus itself buds will often die or be weakened and shed more viral particles for an extended period. The lipid bilayer envelope of these viruses is relatively sensitive to desiccation, heat, and detergents, therefore these viruses are easier to sterilize than non-enveloped viruses, have limited survival outside host environments, and typically must transfer directly from host to host. Enveloped viruses possess great adaptability and can change in a short time in order to evade the immune system. Enveloped viruses can cause persistent infections.

Enveloped Examples

Classes of Enveloped Viruses that contain Human Pathogens:

DNA viruses

• Herpesviruses
• Poxviruses
• Hepadnaviruses

RNA viruses

• Flavivirus
• Togavirus
• Coronavirus
• Hepatitis D
• Orthomyxovirus
• Paramyxovirus
• Rhabdovirus^[2]
• Bunyavirus
• Filovirus

Retroviruses

• Retroviruses

Nonenveloped Examples

Classes of Nonenveloped Viruses that contain Human Pathogens:

DNA viruses

• Adenoviridae

RNA viruses

• Picornaviridae

See also

• Bacterial capsule
• Cell envelope

References

External links

• "Virus Structure". Molecular Expressions: Images from the Microscope. Retrieved 2007-06-27.