Epstein-Barr virus

Background

Microbiology

• A gamma-1 herpesvirus
• Double-stranded DNA inside an icosahedral protein nucleocapsid surrounded by a lipid envelope with glycoproteins
• Two strains (type 1 and 2) are serologically identical, but have unique epitopes
• Infection can remain quiescent in B cells for life

Epidemiology

• Acquired via oral secretions, e.g. by kissing or sharing of food
• Seroprevalence about 90-95% in adults, with about half of 5 year-olds already being seropositive
• Highest morbidity is with young adults who develop infectious mononucleosis during primary disease
  • Includes barracks and universities

Pathophysiology

• Acquired through mucous membrane contact of oral secretions
• Immune response primarily with cytotoxic T cells and NK cells
  • Atypical lymphocytosis develops from CD8 cells
• Early response is against lytic antigens (including VCA and EA), and later response against latent proteins (EBNA1, EBNA2, EBNA3, and EBNALP)
• Response also creates IgM antibodies to sheep, horse, and cow RBCs, called heterophile antibodies

Clinical Presentation

Childhood

• In childhood, mostly asymptomatic or mild febrile illness
• May develop rashes, neutropenia, or pneumonia
• Can cause lymphadenopathy
• Heterophile antibody may be negative if young; about 80% are positive by 4 years, though

Infectious mononucleosis

• Caused by primary infection, typically in an adolescent or young adult
• Incubation period 30 to 50 days, and can have asymptomatic viral shedding for up to a month before symptoms
• Causes about 80% of mononucleosis, with the rest being CMV
• Symptoms include a triad of sore throat, fever, and lymphadenopathy
  • Often preceded by prodromal symptoms of chils, sweats, anorexia, and malaise
  • Can also have retro-orbital headaches, myalgias, and abdominal discomfort
  • May have a rash which can take any form, and may have palatal petechiae
  • Tonsils are sometimes exudative
  • Often has splenomegaly, may have hepatomegaly, and rarely has jaundice
• With exposure to amoxicillin, almost all patients develop a diffuse maculopapular rash
• May have transient heterophile antibodies, as well as atypical lymphocytosis
• Resolves over 2 to 3 weeks, with fevers lasting up to 14 days

Complications

• Linked to a number of malignancies, including Burkitt lymphoma, nasopharyngeal carcinoma, and lymphoproliferative disorders
• Neurologic complications include meningitis, encephalitis, Guillain-Barré syndromes, optic neuritis, retrobulber neuritis, cranial nerve palsies, mononeuritis multiplex, brachial plexus neuropathy, seizures, subacute sclerosing panencephalitis, transverse, myelitis, psychosis, demyelination, and hemiplegia

Diagnosis

Serology

• Anti-VCA (viral capsid antigens): most useful
  • Anti-VCA IgM: appears early and disappears within 4 to 6 weeks
  • Anti-VCA IgG: appears in acute phase, peaks at 2 to 4 weeks, then declines but remains positive for life
• Anti-EA (early antigen) IgG: appears in acute phase and falls to undetectable within 3 to 6 months (but may persist for years)
  • Least useful test
• Anti-EBNA (EBV nuclear antigen): negative during acute phase converts after 2 to 4 months and stays positive for life
• Monospot test: cross-reacts with many other conditions, and is often falsely negative in children

Immunocompetent hosts

VCa-IgM	VCA-IgG	EBNA-IgG	Interpretation
–	–	–	Susceptible
–	–	+	Past infection or non-specific
–	+	–	Acute or past infection
–	+	+	Past infection
+	–	–	Acute infection or non-specific
+	–	+	Uninterpretable
+	+	–	Acute infection
+	+	+	Late primary infection or reactivation

EBV-associated diseases

Disease	VCA-IgM	VCA-IgG	VCA-IgA	EA(D)-IgG	EA(R)-IgG	EA-IgA	EBNA-IgG
Chronic active infection	±	++	±	+	++	–	±
Burkitt lymphoma	–	++	–	±	++	–	+
ENT carcinoma	–	++	+	++	±	+	+
Hodgkin lymphoma	–	++	–	+	–	–	+
Reactivation	±	++	±	+	±	±	±