Epstein-Barr Virus and Lymphoma

Epstein-Barr virus (EBV) is a herpesvirus (one of many from the wider herpesvirus family, including the virus that causes chicken pox as well as the herpes simplex viruses associated with sexual transmission). It is a complex, enveloped DNA virus; once inside the nucleus of the host cell, the virus multiplies.

Experts estimate that between 90-95 percent of the world's adult population is EBV-seropositive. EBV is spread chiefly through saliva. It may cause occasional infections of otherwise unknown origin but ones that are generally considered to be mild. However, in some cases it can cause a severe, even deadly problem; namely, cancer.

The overwhelming majority of people are infected in the oropharyngeal cavity. In developing countries, the population tends to be infected at a young age and they remain without symptoms for the extent of their lives. In developed countries, infection occurs later in life, with as many as half of all infections occurring after adolescence.

EBV and Causes of Cancer

EBV is equipped with a set of genes known to cause growth activation within cells. Since EBV typically infects B-cells, it is believed that the growth activation genes can turn an infected B-cell cancerous. However, what is unclear is the exact mechanism of action for lymphomas, and what seems to be getting clearer is that EBV alone is generally not enough to cause cancer; other factors must also be at work.

The virus is associated with a handful of lymphoma subtypes, as well as nasopharyngeal carcinoma, particularly in China, where that is one of the most commonly diagnosed cancers in the country.

EBV and Lymphoma Sub-Types

Infection by EBV and the development of lymphoma is associated with three major subtypes of lymphoma:

• - Post-transplant lymphomas, since the drugs required following a transplant typically make the patient immunocompromised and therefore susceptible to a host of dormant viruses, EBV being among them;
• - Hodgkin's lymphoma, although the precise association remains unknown. Still, close to half of all Hodgkin's patients are also EBV positive
• - Burkitt's lymphoma, particularly in Africa, where this fast-growing cancer tends to strike children at around age 6 or 7 and is sufficiently widespread for the WHO to call it 'endemic'.

To a much lesser extent, EBV is associated with some T-cell lymphomas, as well as some gastric cancers. According to the WHO, "these tumors are characterized by the presence of multiple extrachromosomal copies of the viral genome in tumor cells and the expression of part of the EBV genome."

Sources:
About Leukemia & Lymphoma
UpToDate.com
World Health Organization: Viral Cancers