Pathogen, pathogenesis, clinical picture. EBV infects only a narrow spectrum of hosts and replicates very slowly. It persists in a latent state in B lymphocytes and can lead to their immortalization and tumor transformation.
EBV enters the body through the mucosa. It replicates in epithelial cells of the oropharynx or cervix and enters B lymphocytes, where it continues to replicate. This results in the clinical picture of infectious mononucleosis (kissing disease or Pfeiffer disease), which is characterized by fever and a generalized but mainly cervical swelling of the lymph nodes, typically accompanied by tonsillitis, pharyngitis, and some cases of mild hepatic involvement. This virus also persists in latency, probably for the life of the patient, in (immortalized) B cells.
EBV and EBV-specific sequences and antigens are isolated in cases of Burkitt lymphoma and nasopharyngeal carcinoma. The higher incidence of Burkitt lymphoma in parts of Africa is attributed to a cofactor arising from the hyperendemic presence of malaria there. EBV exacerbates the B-cell proliferation resulting from a malaria infection. EBV has also been implicated in Hodgkin disease and T-cell lymphomas. These tumor forms also result from the interaction of EBV with other mechanisms of cell damage. In immuno-competent persons, the following lymphoproliferative diseases are sequelae of EBV infections:
— a benign polyclonal B-cell hyperplasia,
— its malignant transformation into a polyclonal B-cell lymphoma, and
— a malignant, oligoclonal or monoclonal B-cell lymphoma.
Diagnosis. Heterogenetic antibodies that agglutinate the erythrocytes of several animal species and antibodies to a variety of viral antigens are found in acute infectious mononucleosis:
— VCA (viral capsid antigen). Antibodies to VCA appear early and persist for life.
— EA (early antigen). Antibodies to EA are only detectable during the active disease.
— EBNA (Epstein-Barr nuclear antigen). Antibodies to EBNA are not produced until two to four weeks after disease manifestation, then persist for life.
Chronic mononucleosis is characterized by antibodies to VCA and EA.
The diagnostic procedures in lymphoproliferative diseases (see above) involve histology and cellular immunotyping.
Epidemiology, prevention, and therapy. EBV is excreted in saliva and pharyngeal secretions and is transmitted by close contact ("kissing disease"). As with all herpesviruses the level of generalized contamination is high, with the process beginning in childhood and continuing throughout adolescence. Neither immunoprophylactic nor chemoprophylactic measures have been developed as yet. Lymphoproliferative diseases involving viral replication can be treated with acyclovir and ganciclovir.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.