The name "herpes" comes from the Greek "herpein" which means to creep. Over 100 herpes viruses have been isolated. There is at least one virus for most animal species that have been researched.
Herpesviridae is the name of the family of enveloped, double-stranded DNA viruses with relatively large and complex genomes. Herpes viruses can enter and replicate in a very wide range of vertebrate hosts. Herpes virus hosts include: humans, horses, cattle, mice, pigs, chickens, turtles, lizards, fish, dogs, cats, and even some invertebrate species, such as oysters!
Whether or not a virus can replicate depends on several strategies. A successful virus must be able to quickly stop its new host cell from replicating and turn over the host cell's metabolism to start replicating virion particles very soon after invasion into the cell.
A successful virus must also be able to avoid the host's immune system attacks. They do this by blocking presentation of antigenic peptides on the cell surface and blocking the host cell from destroying itself (apoptosis). The virus does not want the host cell to die or else it cannot replicate and infect more cells.
Alphaherpesviridae: Herpes viruses in this subfamily infect nervous system tissue. They can replicate in only 18 hours. Members of this subfamily can very efficiently destroy cells and can infect a wide range of animal hosts.
Betaherpesviridae: Members of this subfamily attack the body's lymphocytes. They only infect certain animal hosts and take a long time to replicate. Infected cells become enlarged and swollen.
Gammaherpesviridae: These viruses also infect lymphocytes, but are specific for either B or T lymphocytes.
Herpes viruses can also lie dormant within the nucleus of the cells they infect or within the host's central nervous system. They then return and cause infection up to years later, when the host's immune system is stressed.
Electron micrograph of herpes virus.
Structure of the Herpes Virus
All herpes viruses have four main structural parts:
Core: Inside the core there is a single linear molecule of double-stranded DNA.
Capsid: The core is surrrounded by a protective outer "shell" with a 100 nm diameter constructed of 162 capsomeres.
Tegument: Between the capsid and envelope, there is layer that consists of viral enzymes that are needed in order for the herpes virus to take control of the host cell's metabolic processes. This in turn, allows the herpes virus to successfully replicate inside its new host.
Envelope: This is the outermost layer of the herpes virus. It is composed of an altered host membrane and unique viral glycoproteins. The glycoproteins give the virus a "spikey" appearance.
Stylized drawing of the structure of herpes virus.