Infectious mononucleosis: causes and pathogenesis
Last reviewed: 23.04.2024
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Causes of infectious mononucleosis
The cause of infectious mononucleosis is the Epstein Bar virus attributed to the group of herpes viruses ( Herpesviridae family , Gammaherpesvirinae subfamily , genus Lymphocryptovirus.), Human herpes virus type 4. Contains DNA. Which is in the form of a double helix, in which more than 30 polypeptides are encoded. The virion consists of a capsid with a diameter of 120-150 nm. Surrounded by a membrane containing lipids. The virion capsid has the shape of an icosahedron. EBV has a tropism for B-lymphocytes due to the presence on their surface of receptors for this virus. The virus can persist for a long time in the host cells in a latent form. Has antigenic components, common with other herpes group viruses. Antigenically homogeneous, contains the following specific antigens: viral capsid antigen, nuclear antigen, early antigen and membrane antigen. Antigens of the virus induce the production of antibodies - markers of EBV infection. Sustainability in the environment is low. The virus quickly dies when dried, under the influence of high temperatures (boiling, autoclaving), treatment with all disinfectants.
Unlike other epstein-bar herpetetic viruses, the virus does not kill, but proliferation of affected cells, because it is referred to oncogenic viruses, in particular, it is considered the etiological factor of Burkitt sarcoma, nasopharyngeal carcinoma, B-cell lymphoma, some immunodeficiencies, fibrous leukoplakia of the tongue, with HIV infection. Epstein-Bar virus after primary infection persists in the body for life, integrating into the genome of the affected cells. In case of violations in the immune system and the effects of other factors, the virus can be reactivated.
[Pathogenesis of infectious mononucleosis
When the Epstein-Bar virus enters the saliva with the collar of the infection and the site of its replication, the oropharynx serves. Infection is maintained by B-lymphocytes having surface receptors for the virus, they are considered the main target of the virus. Replication of the virus also occurs in the epithelium of the mucous membrane of the oropharynx and nasopharynx, the ducts of the salivary glands. During the acute phase of the disease, specific viral antigens show in the nuclei more than 20% of circulating B lymphocytes. After the infectious process subsides, viruses can be detected only in single B-lymphocytes and epithelial cells of the nasopharynx.
The virus-infected B-lymphocytes under the influence of virus mutagens begin to proliferate intensively, transforming into plasma cells. As a result of polyclonal stimulation of the B-system, the level of immunoglobulins in the blood increases, in particular, heterogemagglutinins appear that can agglutinate foreign erythrocytes (sheep, horses) that are used for diagnosis. Proliferation of B-lymphocytes also leads to the activation of T-suppressors and natural killers. T-suppressors suppress the proliferation of B-lymphocytes. In the blood, their young forms appear, which morphologically characterize as atypical mononuclear cells (cells with a large nucleus, like the lymphocyte, and a broad basophilic cytoplasm). T-killers destroy infected B-lymphocytes by antibody-dependent cytolysis. Activation of T-suppressors leads to a decrease in the immuno-regulatory index below 1.0, which contributes to the attachment of bacterial infection. Activation of the lymphatic system is manifested by an increase in lymph nodes, tonsils, other lymphoid formations of the pharynx, spleen and liver. Histologically, proliferation of lymphoid and reticular elements, in the liver - periportal lymphoid infiltration. In severe cases necrosis of lymphoid organs is possible, the appearance of lymphoid infiltrates in the lungs, kidneys, central nervous system and other organs.
Epidemiology of infectious mononucleosis
Infectious mononucleosis - anthroponosis; the source of the causative agent of the infection is a sick person, including with the erased form of the disease, and a virus carrier. The epidemic process in the population is supported by virus carriers, persons infected with Epstein-Bar virus, which periodically release the virus into the environment with saliva. In flushes from the oropharynx in seropositive healthy individuals, a virus is detected in 15-25% of cases. When the volunteers were contaminated with washings from the throat of patients with infectious mononucleosis, there were distinct laboratory changes characteristic of EBV-infectious mononucleosis (moderate leukocytosis, an increase in the number of mononuclear leukocytes, increased activity of aminotransferases, heterogemagglutination), but there was no detailed clinical picture of mononucleosis in any case. The frequency of virus isolation increases dramatically with violations in the immune system. The main transmission path is airborne. Infection is also possible through direct contact (with kisses, sexually) and indirect contact through household items, toys contaminated with saliva. Containing virus. Latent infection in B-lymphocytes of peripheral blood from donors creates a risk of infection with blood transfusions.
A person is easily susceptible to the Epstein-Bar virus. The timing of primary infection depends on social conditions. In developing countries and socially disadvantaged families, most children are infected between the ages of 6 months to 3 years. And, as a rule, the disease is asymptomatic; sometimes there is a picture of ARD. The entire population is infected by the age of 18. In developed countries and socially-advantaged families, infection occurs at an older age. More often in adolescence or adolescence. By the age of 35 most of the population is infected. When infected over the age of 3 years, a typical picture of infectious mononucleosis develops in 45%. Immunity in infected infectious mononucleosis is lifelong, non-sterile, repeated diseases are not observed, but various manifestations of EBV infection due to the reactivation of the virus are possible.
Most often they are sick with male faces. Very rarely patients over 40 years old. However, for HIV-infected people, the reactivation of the Epstein-Bar virus can occur at any age.