Epstein-Barr virus (EBV), Infectious Mononucleosis

Sample

• The Serum of the patient is needed.

 Purpose of the test (Indications)

• This test is done to diagnose infectious mononucleosis (EBV).

 Pathophysiology

1. EBV is a herpes virus found throughout the world.
2. This was first diagnosed in 1964 as the causative agent of infectious mononucleosis.
3. It is estimated that 95% of the world population is exposed to this virus.
4. In the USA 80% of the population is infected.
   1. Once there is an infection, the virus becomes dormant and can be reactivated later.
   2. In the USA in a higher socio-economic group, it is seen in later life and considered to be by social contact so-called “kissing diseases”.
5. Infectious mononucleosis is caused by the virus known as Epstein Barr virus(EBV).
   1. This belongs to the Herpes family.
   2. It is 100 nm, double-stranded DNA, icosahedral, enveloped.
   3. It infects the B-lymphocytes.
      1. These B-lymphocytes after the infection looks like T-lymphocytes.
   4. The habitat for the virus is B-lymphocytes and epithelial cells of the oropharynx.
6. Morphology: EBV is an enveloped icosahedral virus containing a double-stranded DNA genome of 172 Kb.
   1. EBV is a lymphotropic virus.
   2. EBV is a member of the herpes virus family.

7. The mode of spread is oropharyngeal secretion.
   1. Also reported by blood transfusion and transplacental routes.
8. The incubation period is 4 to 6 weeks (or 10 to 50 days).
9. This virus usually affects young adults.

10. EBV life cycle:

    1. The EBV enters the B-lymphocytes through the presence of C3d receptors.
    2. Once it is internalized, the cell loses control.
    3. There is cellular proliferation.
    4. EBV becomes the part of DNA and remains latent as EBV-DNA.
    5. Later on, the EBV-DNA cell is activated and starts proliferation.
    6. Now there are the possibilities:
       1. Cells transform into cancer cells.
       2. There may be the resolution of the infectious mononucleosis.
       3. The immune system destroys the infecting virus and abnormal B-lymphocytes.
    7. Or there is cell lysis and the viruses are released.

11. The patient develops Antibodies of IgM type against EBV viral capsid usually after 2 weeks of the disease.
    1. These antibodies readily react and agglutinate with horse RBCs.

Clinical presentation

1. The majority has no signs and symptoms.
2. Infectious mononucleosis may be seen as:
   1. Acute.
   2. Chronic.
   3. This is a benign disease.
   4. This is a self-limiting disease.
3. In children under 5 years of age, the disease is very mild.
   1. This is also seen in adolescents and young adults.
4. After incubation of 10 to 50 days, the disease lasts for 1 to 4 weeks.
   1. Pharyngitis and sore throat.
   2. Fever.
   3. Fatigue, malaise
   4. Exudative tonsillitis is often the presenting feature of the generalized viral infection due to Epstein-Barr virus, the so-called anginose form of infectious mononucleosis.
5. Enlargement of the lymph nodes, mainly cervical lymph nodes is seen.
6. Splenomegaly is seen in 50% of the cases.
7. Jaundice is less common.
8. This also causes oral hairy leukoplakia.
9. The most common complication is hepatitis.
10. Few patients may show hepatomegaly.
11. This is associated with Burkitt’s lymphoma and nasopharyngeal carcinoma.
    1. There may be B- cell lymphoma in the immuno-comprised patient.

12. The complication of infectious mononucleosis are:

    1. Cardiac.
    2. Ocular.
    3. Hematological.
    4. Renal.
    5. Gastrointestinal.
    6. Neurological. This may lead to Bell’s palsy, meningoencephalitis, Guillain Barre’ syndrome, cranial nerve neuritis, myelitis, and psychotic disorders.
    7. Respiratory.

13. Chronic EBV signs and symptoms are variable :

    1. In some cases may be nonspecific symptoms.
       1. There may be severe fatigue (chronic fatigue syndrome).
       2.  Pharyngitis.
       3. Myalgia.
       4. Arthralgia.
       5. Low-grade fever.
       6. Headache.
       7. Paresthesia.
       8. There is a loss of skilled thinking.
14. Laboratory findings show:
    1. Lymphocytosis.
    2. Atypical lymphocytes. These are large activated T-lymphocytes.
    3. Transient serum heterophilic antibodies are seen in the acute phase.
15. Infectious Mononucleosis is associated with :
    1. In Africa with Burkitt’s lymphoma.
    2. In China with nasopharyngeal carcinoma.
    3. Nasal T/NK-type lymphoma.
    4. Some subtypes of Hodgkin’s lymphoma.
    5. Most of the patients recover uneventfully and come to normal activity within 4 to 6 weeks.

Procedure for lab test

1. Monospot test
   1. These are the heterophil antibody against EBV and react with and agglutinate sheep/horse RBCs.
   2. This test can be used as a screening test.
      1. The serum of the patient is added to slides and has horse RBCs.
      2. It is negative in 30% of the infectious mononucleosis patient.
2. Paul-Bunnel screening test.
3. Davidsohn Differential test.
4. Criteria to label a patient with infectious mononucleosis:
   1. Clinical presentation.
   2. The peripheral blood smear shows lymphocytosis (DLC slide).
   3. There are atypical lymphocytes.
   4. Positive serologic test.
   5. Test (IgM) titer is above 1:56.

Normal

Source 6

• EBV titer = ≤1:10 are nondiagnostic.
• EBV titer of 1:10 to 1:60 indicates infection at some undetermined time.
• EBV titer of  ≥1:320 suggests active infection.
• A fourfold increase in titer in paired sera drawn 10 to 14 days apart is usually indicates an acute infection.

Laboratory diagnosis:

1. Heterophil antibodies are positive in 80 to 90% of the patient.
   1. Monospot slide test for heterophil antibody.
   2. A specific EBV antibody advised in case of the above negative test.
      1. These antibodies are against the viral capsid antigen (Anti-VCA).
2. Molecular biology can detect EBV-DNA.
3. The peripheral blood smear shows atypical lymphocytes.
   1. 5 to 30% are atypical lymphocytes.
   2. These atypical lymphocytes persist for 1 to 2 months,
      1. In some cases, these atypical lymphocytes may persist for 4 to 6 months.
4. 10% of the patients show leucopenia.

Serologic test interpretation:

1. Normally a low concentration of these heterophil bodies is seen.
2. There are three antigens:
   1. Viral capsid antigen = VCA
      1. Antibodies are VCA-IgM and VCA-IgG.
      2. This is detected in the early phase and disappears in2 to 4 months.
   2. Early antigen = EA. This is complex of:
      1.   Early antigen-n-diffuse = EA-D
         1. Anti-EA-D of IgG type is highly indicative of acute infection.
         2. It is absent in 10 to 20% of the patients.
         3. It disappears in about 3 months.
         4. It is present in the nucleus and cytoplasm.
      2. Early antigen-restricted = EA-R
         1. Usually not found in young patients.
         2. It appears transiently in the recovery stage.
         3. It is only present in the cytoplasm.

1. 1. EBV nuclear antigen = EBVNA
      1. It is found in the nucleus of all infected cells.
      2. EBVNA synthesis precedes the EA formation.
         1. Anti-EBVNA does not appear until the patient enters the convalescent stage.
         2. EBVNA antibodies titer continue to rise in the convalescent stage and reach a peak in 3 to 12 months postinfection.
         3. EBVNA antibody titer is high in nasopharyngeal carcinoma and Burkitt’s lymphoma.
            1. EA-D is found in nasopharyngeal carcinoma.
            2. EA-R is found in Burkitt’s lymphoma.
      3. Titer  = ≤1:10 are negative.
      4. Titer  = 1:10 to 1:60 indicate infection.
      5. Titer  = >1:320 indicate acute infection.

 

Antibodies	Appears	Disappears	Stage of the disease
VCA-IgM	7 days	3 months	Acute or recovery stage
VCA-IgG	7 days	Lifelong immunity	Old infection, or acute or recovery stage
EA-D	7 days	2 Weeks	Acute or recovery stage
EA-R	7 days	2 Weeks
EBVNA-IgG	3 weeks	Lifelong immunity	Old infection
Monospot test	5 days	2 weeks	Acute or recovery stage

 Increased IgM (EBV) antibodies are seen in:

1. Infectious mononucleosis.
2. Chronic EBV infection patient.
3. Burkitt’s lymphoma.
4. Chronic fatigue syndrome.
5. Chronic hepatitis.

 

---