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
- EBV is a herpes virus found throughout the world.
- This was first diagnosed in 1964 as the causative agent of infectious mononucleosis.
- It is estimated that 95% of the world population is exposed to this virus.
- In the USA 80% of the population is infected.
- Once there is an infection, the virus becomes dormant and can be reactivated later.
- 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”.
- Infectious mononucleosis is caused by the virus known as Epstein Barr virus(EBV).
- This belongs to the Herpes family.
- It is 100 nm, double-stranded DNA, icosahedral, enveloped.
- It infects the B-lymphocytes.
- These B-lymphocytes after the infection looks like T-lymphocytes.
- The habitat for the virus is B-lymphocytes and epithelial cells of the oropharynx.
- Morphology: EBV is an enveloped icosahedral virus containing a double-stranded DNA genome of 172 Kb.
- EBV is a lymphotropic virus.
- EBV is a member of the herpes virus family.
- The mode of spread is oropharyngeal secretion.
- Also reported by blood transfusion and transplacental routes.
- The incubation period is 4 to 6 weeks (or 10 to 50 days).
- This virus usually affects young adults.
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EBV life cycle:
- The EBV enters the B-lymphocytes through the presence of C3d receptors.
- Once it is internalized, the cell loses control.
- There is cellular proliferation.
- EBV becomes the part of DNA and remains latent as EBV-DNA.
- Later on, the EBV-DNA cell is activated and starts proliferation.
- Now there are the possibilities:
- Cells transform into cancer cells.
- There may be the resolution of the infectious mononucleosis.
- The immune system destroys the infecting virus and abnormal B-lymphocytes.
- Or there is cell lysis and the viruses are released.
- The patient develops Antibodies of IgM type against EBV viral capsid usually after 2 weeks of the disease.
- These antibodies readily react and agglutinate with horse RBCs.
Clinical presentation
- The majority has no signs and symptoms.
- Infectious mononucleosis may be seen as:
- Acute.
- Chronic.
- This is a benign disease.
- This is a self-limiting disease.
- In children under 5 years of age, the disease is very mild.
- This is also seen in adolescents and young adults.
- After incubation of 10 to 50 days, the disease lasts for 1 to 4 weeks.
- Pharyngitis and sore throat.
- Fever.
- Fatigue, malaise
- 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.
- Enlargement of the lymph nodes, mainly cervical lymph nodes is seen.
- Splenomegaly is seen in 50% of the cases.
- Jaundice is less common.
- This also causes oral hairy leukoplakia.
- The most common complication is hepatitis.
- Few patients may show hepatomegaly.
- This is associated with Burkitt’s lymphoma and nasopharyngeal carcinoma.
- There may be B- cell lymphoma in the immuno-comprised patient.
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The complication of infectious mononucleosis are:
- Cardiac.
- Ocular.
- Hematological.
- Renal.
- Gastrointestinal.
- Neurological. This may lead to Bell’s palsy, meningoencephalitis, Guillain Barre’ syndrome, cranial nerve neuritis, myelitis, and psychotic disorders.
- Respiratory.
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Chronic EBV signs and symptoms are variable :
- In some cases may be nonspecific symptoms.
- There may be severe fatigue (chronic fatigue syndrome).
- Pharyngitis.
- Myalgia.
- Arthralgia.
- Low-grade fever.
- Headache.
- Paresthesia.
- There is a loss of skilled thinking.
- In some cases may be nonspecific symptoms.
- Laboratory findings show:
- Lymphocytosis.
- Atypical lymphocytes. These are large activated T-lymphocytes.
- Transient serum heterophilic antibodies are seen in the acute phase.
- Infectious Mononucleosis is associated with :
- In Africa with Burkitt’s lymphoma.
- In China with nasopharyngeal carcinoma.
- Nasal T/NK-type lymphoma.
- Some subtypes of Hodgkin’s lymphoma.
- Most of the patients recover uneventfully and come to normal activity within 4 to 6 weeks.
Procedure for lab test
- Monospot test
- These are the heterophil antibody against EBV and react with and agglutinate sheep/horse RBCs.
- This test can be used as a screening test.
- The serum of the patient is added to slides and has horse RBCs.
- It is negative in 30% of the infectious mononucleosis patient.
- Paul-Bunnel screening test.
- Davidsohn Differential test.
- Criteria to label a patient with infectious mononucleosis:
- Clinical presentation.
- The peripheral blood smear shows lymphocytosis (DLC slide).
- There are atypical lymphocytes.
- Positive serologic test.
- 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:
- Heterophil antibodies are positive in 80 to 90% of the patient.
- Monospot slide test for heterophil antibody.
- A specific EBV antibody advised in case of the above negative test.
- These antibodies are against the viral capsid antigen (Anti-VCA).
- Molecular biology can detect EBV-DNA.
- The peripheral blood smear shows atypical lymphocytes.
- 5 to 30% are atypical lymphocytes.
- These atypical lymphocytes persist for 1 to 2 months,
- In some cases, these atypical lymphocytes may persist for 4 to 6 months.
- 10% of the patients show leucopenia.
Serologic test interpretation:
- Normally a low concentration of these heterophil bodies is seen.
- There are three antigens:
- Viral capsid antigen = VCA
- Antibodies are VCA-IgM and VCA-IgG.
- This is detected in the early phase and disappears in2 to 4 months.
- Early antigen = EA. This is complex of:
- Early antigen-n-diffuse = EA-D
- Anti-EA-D of IgG type is highly indicative of acute infection.
- It is absent in 10 to 20% of the patients.
- It disappears in about 3 months.
- It is present in the nucleus and cytoplasm.
- Early antigen-restricted = EA-R
- Usually not found in young patients.
- It appears transiently in the recovery stage.
- It is only present in the cytoplasm.
- Early antigen-n-diffuse = EA-D
- Viral capsid antigen = VCA
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- EBV nuclear antigen = EBVNA
- It is found in the nucleus of all infected cells.
- EBVNA synthesis precedes the EA formation.
- Anti-EBVNA does not appear until the patient enters the convalescent stage.
- EBVNA antibodies titer continue to rise in the convalescent stage and reach a peak in 3 to 12 months postinfection.
- EBVNA antibody titer is high in nasopharyngeal carcinoma and Burkitt’s lymphoma.
- EA-D is found in nasopharyngeal carcinoma.
- EA-R is found in Burkitt’s lymphoma.
- Titer = ≤1:10 are negative.
- Titer = 1:10 to 1:60 indicate infection.
- Titer = >1:320 indicate acute infection.
- EBV nuclear antigen = EBVNA
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:
- Infectious mononucleosis.
- Chronic EBV infection patient.
- Burkitt’s lymphoma.
- Chronic fatigue syndrome.
- Chronic hepatitis.