Measles: causes and pathogenesis

Causes of measles

The cause of measles is a virus that was isolated by scientists D. Enders and T. Peebles from the body of a sick person in 1954. The measles virus is a shell single-stranded virus with a negative RNA genome, the genus Morbilivirus, the family Paramyxoviridae, has a special affinity for mucopolysaccharides and glycoproteins, in particular to cellular receptors containing sialic acid. The place of synthesis of RNA paramyxoviruses is the cytoplasm of affected cells, there is no need for priming to initiate transcription. The viral particle is pleomorphic, has a rounded shape, a membrane envelope and a spiral nucleocapsid formed by three proteins of the virus and RNA. Nucleocapsid is surrounded by an outer membrane of the matrix protein, which carries surface glycoproteins forming protrusions (aspermometers): conical (hemagglutinin H) and dumbbell (fusion protein F), resulting in hemagglutinating and hemolyzing activity. During reproduction the measles virus causes the formation of multinucleated giant cells-symplasts and eosinophilic inclusions. Multi-nuclear cells are formed by the fusion of membranes of nearby cells. Formation of a child measles virus occurs by "budding" on the surface of infected cells.

In the dried state at a temperature of -20 ° C, measles virus does not lose activity during the year. At a temperature of 37 ° C, inactivation of 50% of the virus population occurs in 2 hours, at 56 ° C the virus dies after 30 minutes, at 60 ° C instantaneously. It is inactivated by 0.00025% formalin solution, sensitive to ether, acid medium (pH <4.5).

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Pathogenesis of measles

The entrance gate of the infection is the mucosa of the upper respiratory tract. The measles virus multiplies in epithelial cells, in particular, in the epithelium of the respiratory tract. The electron microscopy of the material taken from the Filatov-Belsky-Koplikai maculae of skin rashes reveals clusters of the virus. From the last days of incubation within 1-2 days after the appearance of the rash, the virus can be isolated from the blood. The measles virus is hematogenously spread throughout the body, fixed in the organs of the reticuloendothelial system, where it multiplies and accumulates. At the end of the incubation period there is a second, more intense wave of viremia. The causative agent has a pronounced epitheliotropy and affects the skin, conjunctiva, mucous membranes of the respiratory tract, the oral cavity (Filatova-Belski-Koplik stains) and intestines. The measles virus can also be found in the mucous membrane of the trachea, bronchi, sometimes in the urine.

In some cases, the virus can be entered into the brain, causing specific measles encephalitis. In hyperplastic lymphoid tissues, in particular in lymph nodes, tonsils, spleen, thymus, giant reticuloendotheliocytes (Wortin-Finkeldei cells) can be found. In many leukocytes, the destroyed chromosomes are detected. The epithelium of the respiratory tract can necrotize, which facilitates the attachment of a secondary bacterial infection. From the 3rd day of the rash, the virusesemia sharply decreases, and from the 4th day the virus is usually not detected, from this time in the blood begin to show virus neutralizing antibodies. When measles develops a specific allergic alteration of the body, which lasts for a long time. Inoculated with time sharply reduced titers of antibodies to the measles virus, while allergization persists for a long time, which causes the atypical course of the disease 5-7 years after vaccination. Measles leads to a state of anergy, which is manifested by the disappearance of allergic reactions (to tuberculin, toxoplasmin) in infected individuals, as well as exacerbation of chronic bacterial infections.