Structure and Antigenic Composition
EBV virions were first discovered using electron microscopy in biopsy samples of Burkitt lymphoma. The pathogenicity of the virus and its ability to evade the immune response are determined by a complex set of antigens and molecules:
- VCA (Viral Capsid Antigen): A viral capsid antigen that plays a key role in the early stages of infection.
- EBNAs (Epstein–Barr Nuclear Antigens): A group of nuclear antigens (types 1, 2, 3A, 3B, 3C). By nature, these are DNA-binding proteins. The EBNA-1 protein is critical for the development of the infection itself, while EBNA-2 is responsible for the immortalization (infinite division) of infected cells.
- LMPs (Latent Membrane Proteins): Latent membrane proteins of types 1 and 2. These exhibit pronounced oncogene-like activity by interfering with the cell cycle.
- EBERs (Epstein–Barr Encoded RNAs): Small viral RNAs (EBER1 and EBER2) involved in regulating viral activity.
Epidemiology and Pathogenesis
The infection has low contagiousness; the source of transmission is an infected person or an asymptomatic viral carrier. Transmission occurs primarily via airborne droplets or close contact (through saliva). There is a high level of herd immunity in the population, with specific antibodies detected in the overwhelming majority of people.
The portal of entry is the mucous membrane of the oropharynx. The virus finds its main target—B lymphocytes—by binding to their surface receptor CD21. Upon entry, EBV does not simply destroy the cell; instead, it acts as a mitogen, stimulating the active multiplication (proliferation) of B lymphocytes.
The infection tends toward latency. The virus persists for life in B cells and forms hidden reservoirs in lymphoid tissue (primarily the palatine tonsils), as well as in oropharyngeal epithelial cells and salivary glands. Even after clinical recovery (during convalescence), the virus continues to be actively shed from the nasopharyngeal and oral mucous membranes for several months.
Clinical Forms: Mononucleosis and Chronic Infection
Epstein-Barr virus can cause asymptomatic carriage, as well as acute and chronic forms of disease.
Acute Form (Infectious Mononucleosis) This is the classic manifestation of primary contact with the virus. The disease is accompanied by severe malaise and high fever. Mononucleosis is characterized by a classic clinical triad:
- Oropharyngeal involvement (pronounced tonsillopharyngitis involving the palatine and pharyngeal tonsils).
- Lymphadenopathy (generalized enlargement of lymph nodes).
- Hepatosplenomegaly (enlargement of the liver and spleen).
Marked intoxication and specific changes in the complete blood count are also observed.
Chronic Infection May present as a cyclic recurrent disease. The main symptoms are vague: persistent low-grade fever, sore throat, headaches, and pathological fatigue.
In patients with AIDS, a specific oral mucosal lesion occurs—oral hairy leukoplakia—which is considered an important marker condition.
Oncogenesis and Lymphoproliferative Diseases
Because EBV is a potent mitogen for B lymphocytes, it possesses direct oncogenic potential. The risk of tumor development directly depends on the competence of cell-mediated (T-cell) immunity.
In risk groups (patients with T-cell immune defects, HIV infection, genetic X-linked lymphoproliferative disease, and individuals receiving immunosuppressive therapy in transplantation), severe pathologies may develop instead of classic mononucleosis: a polyclonal leukemia-like B-cell disease or various lymphomas.
Specific tumors associated with the virus:
- Burkitt Lymphoma: An African endemic form whose development is closely linked to malaria.
- Hodgkin Lymphoma: In a significant proportion of cases, tumor cells contain viral DNA.
- Nasopharyngeal Carcinoma: Endemic to Eastern countries. Unlike lymphomas, this pathology affects epithelial cells rather than lymphoid cells, and viral DNA is also detected within them.
Immunity and Laboratory Diagnostics
Specific antiviral drugs and vaccines against EBV have not yet been developed. The immunity that forms is durable—cases of recurrent disease are not described. Cytotoxic CD8+ lymphocytes play the primary role in the cellular response, while the production of specific antibodies drives the humoral response.
Diagnostics rely on several methods:
- Hematological Analysis: Pronounced lymphocytosis is characteristic, with monocytes/mononuclear cells accounting for 60–70% of all leukocytes. A key marker of mononucleosis is the appearance of atypical lymphocytes (mononuclear cells) in the blood, comprising about 30% of cells.
- Serology (ELISA):
- Acute (recent) infection: Class M immunoglobulins to the viral capsid antigen (VCA IgM) are detected, and a rising titer of antibodies to the nuclear antigen (EBNA) is observed.
- Peak or past infection: IgG to the VCA antigen appear.
- Auxiliary Methods: Detection of heterophile antibodies using the sheep erythrocyte agglutination test.