++
The Epstein-Barr virus (EBV) is recognized as the major cause
of heterophil-positive and heterophil-negative infectious mononucleosis.
Manifestations of EBV infection are varied and range from asymptomatic
infection to fulminant lymphoproliferative disease. The virus is
associated with a number of malignancies, including African Burkitt
lymphoma, nasopharyngeal carcinoma, Hodgkin disease, and a spectrum
of posttransplant lymphoproliferative diseases. The specific role
of EBV in each tumor is now defined, in a number of circumstances,
to the level of specific cell type and receptors, intracellular
pathways, gene expression, and cytokine production.
++
It is important to recognize that acute primary Epstein-Barr
virus (EBV) infection is not synonymous with infectious mononucleosis.
Most EBV infections acquired at any age, but particularly during
childhood, are asymptomatic. Seroepidemiologic studies demonstrate
that from 20% to 100% of children worldwide have
antibodies to EBV by 6 years of age.9 In contrast,
in the United States, only 40% to 50% of adolescents
are seropositive,9-11 with higher socioeconomic
groups being less likely to have evidence of prior infection. Seropositivity
increases with age in all populations, so that almost all adults have
serologic evidence of past EBV infection. Seroconversion is particularly
high in college, where 10% to 15% of susceptible
persons become infected each year. This group of EBV-naive adolescents
in industrialized countries is susceptible to develop EBV-associated
IM, much more common in the United States and Western Europe than
in unindustrialized countries.
++
EBV is excreted in oropharyngeal secretions (low titer of virus
even during acute illness) and is transmitted by contact with saliva
via kissing or other mucosal contact with contaminated objects.12 Healthy
seropositive individuals intermittently shed EBV into their oropharynx.
Blood products or transplanted tissues can transmit EBV and are
particularly problematic for seronegative immunocompromised transplant
recipients. There is no evidence of urinary or fecal excretion.
Transplacental transmission appears to be rare. Shedding of virus
appears to be more frequent in immunosuppressed individuals, 60% of
whom may excrete EBV at any one time. Because virus shedding is
of a low titer in even immunocompromised patients, standard precautions
are adequate for isolation of patients with acute or past EBV infections.12
++
The epidemiology of infectious mononucleosis is closely related
to the age of primary EBV infection. In the United States, the incidence
of infectious mononucleosis is approximately 50 per 100,000 persons
per year, but in individuals 15 to 25 years old, the incidence doubles.13 Those
areas where children are infected at an early age have the lowest
incidence of the disease. Among susceptible adolescents and young adults,
studies measuring both apparent and inapparent EBV infections indicate
a clinical-to-subclinical ratio of 1:2 to 1:3. Although the ratio of
clinical-to-subclinical infections in young children is not well
defined, the incidence of the typical infectious mononucleosis syndrome
is low.
++
Epstein-Barr virus (EBV) is a member of the family Herpesviridae (gamma
herpesvirus), which contains linear double-stranded DNA surrounded ...