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Viral structure
Herpes viruses all share a common structure—all herpesviruses are composed of relatively large double-stranded, linear DNA genomes encoding 100-200 genes encased within an icosahedral protein cage called the capsid which is itself wrapped in a lipid bilayer membrane called the envelope. This particle is known as the virion.
Herpes virus life-cycle
All Herpes viruses are nuclear-replicating—the viral DNA is transcribed to RNA within the infected cell's nucleus.
Infection is initiated when a viral particle contacts a cell with specific types of receptor molecules on the cell surface. Following binding of viral envelope glycoproteins to cell membrane receptors, the virion is internalized and dismantled, allowing viral DNA to migrate to the cell nucleus. Within the nucleus, replication of viral DNA and transcription of viral genes occurs.
During symptomatic infection, infected cells transcribe lytic viral genes. In some host cells, a small number of viral genes termed latency associated transcript (LAT) accumulate instead. In this fashion the virus can persist in the cell (and thus the host) indefinitely. While primary infection is often accompanied by a self-limited period of clinical illness, long-term latency is symptom-free.
Reactivation of latent viruses has been implicated in a number of diseases (e.g. Shingles). Following activation, transcription of viral genes transitions from latency-associated LAT to multiple lytic genes; these lead to enhanced replication and virus production. Often, lytic activation leads to cell death. Clinically, lytic activation is often accompanied by emergence of non-specific symptoms such as low grade fever, headache, sore throat, malaise, and rash as well as clinical signs such as swollen or tender lymph nodes and immunological findings such as reduced levels of natural killer cells.
Human herpesviridae infections
There are eight distinct viruses in this family known to cause disease in humans.| Human Herpesvirus (HHV) classification | |||
| Type | Synonym | Subfamily | Pathophysiology |
|---|---|---|---|
| HHV-1 | Herpes simplex virus-1 (HSV-1) | α (Alpha) | Oral and/or genital herpes (predominantly orofacial) |
| HHV-2 | Herpes simplex virus-2 (HSV-2) | α | Oral and/or genital herpes (predominantly genital) |
| HHV-3 | Varicella zoster virus (VZV) | α | Chickenpox and shingles |
| HHV-4 | Epstein-Barr virus (EBV), lymphocryptovirus | γ (Gamma) | Infectious mononucleosis, Burkitt's lymphoma, CNS lymphoma in AIDS patients, post-transplant lymphoproliferative syndrome (PTLD), nasopharyngeal carcinoma, HIV-associated hairy leukoplakia |
| HHV-5 | Cytomegalovirus (CMV) | β (Beta) | Infectious mononucleosis-like syndrome, retinitis, etc. |
| HHV-6, -7 | Roseolovirus | β | Sixth disease (roseola infantum or exanthem subitum) |
| HHV-8 | Kaposi's sarcoma-associated herpesvirus (KSHV), a type of rhadinovirus | γ | Kaposi's sarcoma, primary effusion lymphoma, some types of multicentric Castleman's disease |
Zoonotic infections
In addition to the Herpes viruses considered endemic in humans, some viruses associated primarily with animals may infect humans. These are zoonotic infections:
| Zoonotic Herpesviruses | ||||
| Species | Type | Synonym | Subfamily | Human Pathophysiology |
|---|---|---|---|---|
| Macaque monkey | CeHV-1 | Cercopithecine herpesvirus-1, (Monkey B virus) | α | Very unusual, with only approximately 25 human cases reported. Untreated infection is often deadly; sixteen of the 25 cases resulted in fatal encephalomyelitis. At least four cases resulted in survival with severe neurologic impairment. Symptom awareness and early treatment are important for laboratory workers facing exposure. |
| Mouse | MHV-68 | Murine gammaherpesvirus-68 | γ | Zoonotic infection found in 4.5% of general population and more common in laboratory workers handling infected mice. ELISA tests show factor-of-four (x4) false positive results, due to antibody cross-reaction with other Herpes viruses. |
Animal herpesviridae
In animal virology the most important herpesviruses belong to the Alphaherpesvirinae. Research on pseudorabies virus (PrV), the causative agent of Aujeszky's disease in pigs, has pioneered animal disease control with genetically modified vaccines. PrV is now extensively studied as a model for basic processes during lytic herpesvirus infection, and for unravelling molecular mechanisms of herpesvirus neurotropism, whereas bovine herpesvirus 1, the causative agent of bovine infectious rhinotracheitis and pustular vulvovaginitis, is analyzed to elucidate molecular mechanisms of latency. The avian infectious laryngotracheitis virus is phylogenetically distant from these two viruses and serves to underline similarity and diversity within the Alphaherpesvirinae.- Subfamily Alphaherpesvirinae
- Genus Simplexvirus
- Bovine herpesvirus 2 causes bovine mammillitis and pseudo-lumpyskin disease.
- Cercopithecine herpesvirus 1, also known as Herpes B virus, causes a Herpes simplex-like disease in Macaques.
- Ateline herpesvirus 1, Spider monkey herpesvirus.
- Genus Varicellovirus
- Bovine herpesvirus 1 causes infectious bovine rhinotracheitis, vaginitis, balanoposthitis, and abortion in cattle.
- Bovine herpesvirus 5 causes encephalitis in cattle.
- Caprine herpesvirus 1 causes conjunctivitis and respiratory disease in goats.
- Porcine herpesvirus 1 causes pseudorabies.
- Equine herpesvirus 1 causes abortion in horses.
- Equine herpesvirus 3 causes coital exanthema in horses.
- Equine herpesvirus 4 causes rhinopneumonitis in horses.
- Canine herpesvirus 1 causes a severe hemorrhagic disease in puppies.
- Feline herpesvirus 1 causes feline viral rhinotracheitis and keratitis in cats.
- Duck herpesvirus 1 causes duck plague.
- Genus Mardivirus
- Gallid herpesvirus 2 causes Marek's disease.
- Gallid herpesvirus 3 (GaHV-3 or MDV-2)
- Herpesvirus of turkeys (HVT)
- Genus Iltovirus
- Gallid herpesvirus 1 causes infectious laryngotracheitis in birds.
- Subfamily Betaherpesvirinae
- Porcine herpesvirus 2 causes inclusion body rhinitis in swine.
- Subfamily Gammaherpesvirinae
Taxonomy
The following genera are included here:
- Subfamily Alphaherpesvirinae
- Genus Simplexvirus; type species: Human herpesvirus 1 or Herpes simplex; diseases: cold sores, genital herpes, encephalitis
- Genus Varicellovirus; type species: Human herpesvirus 3 or Varicella-zoster virus; diseases: chickenpox, shingles
- Genus Mardivirus; type species: Gallid herpesvirus 2
- Genus Iltovirus; type species: Gallid herpesvirus 1
- Subfamily Betaherpesvirinae
- Genus Cytomegalovirus; type species: Human herpesvirus 5; diseases: mononucleosis
- Genus Muromegalovirus; type species: Murid herpesvirus 1
- Genus Roseolovirus; type species: Human herpesvirus 6; diseases: erythema subitum, roseola infantum
- Subfamily Gammaherpesvirinae
- Genus Lymphocryptovirus; type species: Human herpesvirus 4 or Epstein-Barr virus; diseases: mononucleosis, Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease
- Genus Rhadinovirus; type species: Human Herpesvirus 8, Saimiriine herpesvirus 2
- Unassigned
- Genus Cercopithecine; type species: Cercopithecine herpesvirus 1
- Genus Ictalurivirus; type species: Ictalurid herpesvirus 1
See also
References
External links
- International Herpes Management Forum
- http://www.cdc.gov/ncidod/diseases/bvirus.pdf PDF Article on Cercopithecine herpesvirus
- http://www.gsu.edu/bvirus National B Virus Resource Center
- Animal viruses
This article is licensed under the GNU Free Documentation License.
Last updated on Wednesday May 28, 2008 at 10:19:31 PDT (GMT -0700)
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