Epstein-Barr virus

From Free net encyclopedia

? Epstein-Barr virus Template:Taxobox begin placement virus Template:Taxobox group i entry
Family:	Herpesviridae
Genus:	Lymphocryptovirus
Species:	Human herpesvirus 4 (HHV-4)

|} The Epstein-Barr virus (EBV), also called Human herpesvirus 4 (HHV-4), is a virus of the herpes family (which includes Herpes simplex virus and Cytomegalovirus), and is one of the most common viruses in humans. Most people become infected with EBV, which is usually asymptomatic. It is named after Michael Epstein and Yvonne Barr, who discovered the virus in 1964.

1 Properties
2 Pathogenesis
3 Infectious mononucleosis
4 Role in disease
5 Diseases associated with EBV
6 References
7 External links

[edit]

Properties

Epstein-Barr virions are enveloped and spherical. They have a diameter of 120-220nm. There are small spikes on the surface of the virions, giving it a rough texture. The total genome length for this virus is 170,000 nt.[1]

[edit]

Pathogenesis

Epstein-Barr virus primarily infects B cells, where it forms a latent infection that persists for life.

[edit]

Infectious mononucleosis

Epstein-Barr can cause Infectious mononucleosis, also known as 'glandular fever' or 'Mono'. Infectious mononucleosis is caused when a person is first exposed to the virus during or after adolesence. It is therefore predominantly found in the developed world, as most children in the developing world are found to be already infected by around 18 months of age. EBV antibody tests turn up almost universally positive in developing nations, but only 70-80% positive in the United States.

[edit]

Role in disease

Epstein-Barr was the first virus to be identified as an oncovirus, meaning that it is associated with the development of cancer.

The difficulty with proving a link between a cancer type and EBV infection, is that EBV is a ubiquitous virus, which infects most people. Therefore, EBV is usually seen as a co-factor in cancer development, which may act together with other contributing factors.

It is now thought to be associated in the formation of a variety of tumors that include lymphomas and leukemias, carcinomas and sarcomas. Recently the virus has been implicated as a co-factor in invasive breast cancer.

The strongest evidence linking EBV and cancer formation is found in Burkitt's lymphoma and Nasopharyngeal carcinoma.

Burkitt's lymphoma is a type of Non-Hodgkin's lymphoma [2] and is most common in equatorial Africa and is co-existent with the presence of malaria. Malaria infection causes reduced immune surveillance of EBV immortalised B cells, so allowing their proliferation. This proliferation increases the chance of a mutation to occur. Repeated mutations can lead to the B cells escaping the body's cell-cyle control, so allowing the cells to proliferate unchecked, resulting in the formation of Burkitt's lymphoma. Burkitt's lymphoma commonly affects the jaw bone, forming a huge tumour mass. It responds quickly to chemotherapy treatment, namely cyclophosphamide, but recurrence is common.

Other B cell lymphomas arise in immunocompromised patients such as those with AIDS or who have undergone organ transplantation with associated immunosuppression. Smooth muscle tumors are also associated with the virus in immunocompromised patients.

Nasopharyngeal carcinoma is a cancer found in the upper respiratory tract, most commonly in the nasopharynx, and is linked to the EBV virus. It is found predominantly in Southern China and Africa, due to both genetic and environmental factors. It is much more common in people of Chinese ancestry (genetic), but is also linked to the Chinese diet of a high amount of smoked fish, which contain nitrosamines, well known carcinogens (environmental).

In the late 1980s and early 1990s, EBV became the favoured explanation for chronic fatigue syndrome. It was noted that people complaining of characteristic exhaustion had EBV, although it was also noted EBV was present in almost everyone, even those not complaining of exhaustion. In a four year study, the Centers for Disease Control and Prevention found no association between CFS and infection by a wide variety of human pathogens, including EBV. See chronic fatigue syndrome.

[edit]