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Infectious Disease and Microbiology: Infectious Mononucleosis
Infectious mononucleosis (IM), also known as glandular fever, is a common self-limiting clinical syndrome caused primarily by Epstein–Barr virus. It is characterized by acute onset of fever, sore throat, lymphadenopathy, and atypical lymphocytosis. EBV is transmitted mainly through saliva, which is why the illness is often called the “kissing disease.” After infection, the virus persists lifelong in the host.
IM is common worldwide. In industrialized countries, EBV infection often occurs either in early childhood, when it is usually asymptomatic, or in late adolescence, when it is more likely to cause symptomatic mononucleosis. By adulthood, 90–95% of people have evidence of prior EBV infection. Risk factors include close contact with an infected person and immunosuppression, especially in transplant recipients. In rare cases, certain inherited immune defects can lead to severe, even life-threatening EBV infection.
The pathophysiology begins when EBV infects the oropharyngeal epithelium and then B lymphocytes. The immune response, especially proliferation of cytotoxic CD8+ T lymphocytes, is responsible for much of the clinical syndrome. These activated lymphocytes appear as atypical lymphocytes on the blood smear. Although the immune response controls the primary infection, EBV remains latent for life.
Clinically, young children are often asymptomatic or have only mild illness. In adolescents and young adults, the disease usually begins with fatigue, malaise, and myalgias, followed by fever and sore throat. Common symptoms include fever, sore throat, malaise, headache, anorexia, myalgias, and sometimes abdominal pain, nausea, or vomiting. On examination, patients commonly have cervical lymphadenopathy, pharyngitis or tonsillitis, splenomegaly, and sometimes hepatomegaly. Less common findings include palatal petechiae, periorbital edema, rash, and jaundice. A maculopapular rash may occur, especially after exposure to ampicillin or amoxicillin.
Diagnosis is usually supported by laboratory findings. Atypical lymphocytosis and relative or absolute lymphocytosis are common. Mild thrombocytopenia and elevated liver enzymes may also be present. Heterophile antibody tests such as the Monospot are widely used and are fairly sensitive and specific in symptomatic patients, although they may be negative early in illness or in young children. EBV-specific serology, including viral capsid antigen and EBV nuclear antigen antibodies, can help confirm the diagnosis when needed. Ultrasound may be used to assess splenomegaly, especially in athletes.
Treatment is mainly supportive. Most patients only need rest, fluids, and symptom relief with acetaminophen or nonsteroidal anti-inflammatory drugs. Corticosteroids are reserved for severe complications such as impending airway obstruction, severe thrombocytopenia, hemolytic anemia, myocarditis, pericarditis, or neurologic complications. Patients should avoid contact sports and strenuous physical activity for at least 3–4 weeks, or longer if splenomegaly persists, because of the risk of splenic rupture. Beta-lactam antibiotics such as ampicillin and amoxicillin should be avoided unless clearly indicated for another reason.
The prognosis is generally excellent, and most cases resolve within 1–2 weeks. However, fatigue may persist for weeks or even months in some patients. Complications are uncommon but may include autoimmune hemolytic anemia, thrombocytopenia, airway obstruction, hepatitis, myocarditis, pericarditis, neurologic syndromes, pneumonia, splenic rupture, and lymphoproliferative disorders in susceptible individuals.
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