Mononucleosis

Description

• Results in most cases from infection with the Epstein–Barr virus (EBV) (a herpesvirus):
  • Non-EBV causes of infectious mononucleosis (IM):
    • Cytomegalovirus (CMV)
    • Adenovirus
    • Hepatitis A
    • Herpesvirus 6
    • HIV
    • Rubella
    • Toxoplasma gondii
    • Group A β-hemolytic streptococci
• >90% of adults on serologic testing demonstrate prior infection with EBV:
  • Most do not recollect specific IM symptoms
• Mode of transmission is close or intimate contact particularly with saliva from “shedders” who may or may not be symptomatic:
  • Nickname “kissing disease”
  • Viral shedding in saliva can persist intermittently for life
  • May occur after transfusions/transplants
• Incubation period: 4–6 wk
• Immunologic response:
  • T-cells response:
    • T-cell response is responsible for an elevated absolute lymphocyte count and the associated clinical symptoms and complications
    • Subtype of the T-cell lineage, cytotoxic CD8 cells (Downey cells), contain eccentrically placed and lobulated nuclei with vacuolated cytoplasm: The “atypical lymphocytes” seen on differential
  • B-cell response:
    • EBV infects and replicates in B-cells
    • B-cells are then transformed into plasmacytoid cells that secrete immunoglobulins
    • IgM antibody secreted: The heterophile antibody which is reactive against red cell antigens
• Mortality from IM is rare, but may occur due to the following complications:
  • Airway edema
  • Neurologic complications
  • Secondary bacterial infection
  • Splenic rupture
  • Hepatic failure
  • Myocarditis
• EBV infection has also been strongly linked to African Burkitt lymphoma and nasopharyngeal carcinoma

• In children <4 yr, infection with EBV is often asymptomatic
• In children who do become symptomatic, there is propensity toward atypical presentations:
  • Neutropenia, pneumonia, and varied rashes
  • Mesenteric lymphadenopathy and splenomegaly can cause the illness to present with abdominal pain and be confused with appendicitis
  • Infants and toddlers can present with only irritability and failure to thrive so must be considered when no other source can be identified