infectious mononucleosis
Pathophysiology

Infectious mononucleosis is also known as glandular fever or mono. 

 

It is caused by Epstein Barr Virus (EBV), which is a member of the herpes virus family. 

 

EBV spreads through saliva, which is why kissing and sharing drinks or utensils is a common mode of transmission. 

 

The virus first infects the epithelial cells of the oropharynx (tonsils and salivary glands), then spreads to the blood stream where it  infects B lymphocytes cells.

 

The infected B cells then begin to proliferate and travel to surrounding lymphoid tissue in the spleen and lymph nodes.

 

Here, the body mounts an immune response releasing cytotoxic T cells which undergo massive activation and proliferation to handle the viral load. As they activate, they take on an atypical appearance with large, irregular nuclei.

 

This immune activation leads to hyperplasia of lymphoid tissue in the tonsils, lymph nodes and the spleen.

Epidemiology
  • Adolescents and young adults aged 15–25 years.
  • Children can also get the disease, however they are commonly asymptomatic.
  • Equally common in both males and females.
  • 95% of people have had EBV infection by the time they are adults.
Clinical Features

Symptoms: 

  • Fever
  • Sore throat
  • Fatigue
  • Rash secondary to commencing antibiotics (amoxicillin or cephalosporins)

Infectious mononucleosis is commonly mistaken for streptococcal pharyngitis which is a bacterial infection of the throat.

 

Patients with EBV are sometimes incorrectly prescribed antibiotics such as amoxicillin or cephalosporins. 

 

This can lead to the development of a very itchy, generalised maculopapular rash that often starts 2 to 3 days after commencing the antibiotic. This can be a hallmark feature that someone has a infectious mononucleosis rather than a bacterial throat infection.

 

The rash is self limiting and is not a true drug allergy so patients are usually be able to tolerate penicillin in the future.

 

Signs:

  • ↑ Temp

  • Bilateral posterior chain cervical lymphadenopathy

  • Tonsillar enlargement

  • Splenomegaly 

Investigations
  • BLOODS
    • ↑  White cell count (WCC)
    • ↑ Atypical lymphocytes
    • ↑ AST
    • ↑ ALT

EBV Serology

This is a blood test can be used to determine the onset of illness. It involves testing for antibodies to the the viral capsid antigen (VCA) which is a protein on the outer-shell of the Epstein-Barr Virus. 

 

In the acute phase, IgM antibodies to the Viral Capsid Antigen become elevated.

 

This is shortly followed by VCA IgG antibodies which peak later in the infection and can also be an indicator of past infection. These usually stay positive for life, so are not helpful in determining timing on its own.

 

Once the virus has become dormant inside the host’s B cells, a special antigen, called the EBV nuclear antigen, is produced inside the infected B cells.

 

An antibody to this antigen, called the EBNA IgG, forms 2-4 months after the acute infection.

 

 

So in an acute infection, VCA IgM and VCA IgG will be positive.

 

In a past infection, VCA IgG and EBNA IgG antibodies will be positive.

 

 

Monospot Test

The Monospot test was previously used to test for EBV. It has now been replaced by EBV Serology.

 

The Monospot test was used to detect heterophile antibodies, which are IgM antibodies often produced by the body in response to infection. They are not specific to the EBV antigen.

 

The monospot test works by mixing the patient’s serum with animal red blood cells. If heterophile antibodies are present, they cause the RBCs to clump and this was a positive test.

 

 

There are three disadvantages of the Monospot test: 

  1. Had read manually and was subjective to operator error
  2. Low Specificity
    • Heterophile antibodies are not specific to EBV and are seen in other viral illnesses such as CMV, Toxoplasmosis, HIV and malignancies 
  3. Low Sensitivity
    • Heterophile antibodies may not be present in the first or second week of illness, and therefore could be falsely-negative early on

Management

Disposition:

  • Outpatient

Supportive Care:

  • Self-limiting infection (lasting 2-3 weeks)
  • Rest
  • Fluids
  • Analgesia
  • Avoid alcohol due to liver derangement
  • Avoid contact sports for 3-4 weeks due to risk of splenic rupture

 

Complications:

  • Splenic rupture
  • Glomerulonephritis
  • Haemolytic anaemia
  • Thrombocytopenia
  • Chronic fatigue
  • In certain individuals, latent (or dormant) EBV infection is also associated with certain cancers, such as Burkitt’s lymphoma.