Rubella virus

Rubella virus is the only member of the genus Rubivirus, which belongs to the family Togaviridae.

Rubella (German measles) is an acute infectious disease characterized by spotted rashes on the skin, catarrhal inflammation of the upper respiratory tract and conjunctiva, enlargement of the cervical lymph nodes and signs of minor general intoxication.

Rubella virus is a typical representative of the togavirus family and is similar in its main characteristics to alpha viruses. The virion is spherical, about 60 nm in diameter, the genome is a positive, unfragmented, single-stranded RNA molecule with a molecular weight of 3 MD. The virus has a supercapsid, on the surface of which there are glycoprotein spikes 6-10 nm long. There are two types of glycoproteins: E1 - has hemagglutinating properties in relation to bird erythrocytes, and E2 - acts as a receptor when interacting with the cell. Both glycoproteins are protective antigens. There is only one serovar of the virus.

The virus is relatively unstable in the external environment, easily inactivated by fat solvents, detergents, at pH below 5.0, at temperatures above 56 °C. It is well preserved when frozen, especially at -70 °C.

Rubella virus reproduces well and causes cytopathic changes in cultures of human amnion cells, rabbit kidneys and Vero monkey kidneys. Degeneration occurs in the affected cells, giant multinucleated cells appear. In other cell cultures, the virus can reproduce without visible changes, but induces the development of interference, which protects against the cytopathic action of other viruses. This is the basis for the standard method of isolating rubella virus, which consists of infecting green monkey kidney cells with the test material and introducing ECHO type II virus or vesicular stomatitis virus into the culture after 7-10 days. If cytopathic changes caused by ECHO virus develop, the material does not contain rubella virus, and, conversely, the absence of cytopathic action of ECHO virus indicates the presence of rubella virus in the test material.

The rubella virus is pathogenic for humans, macaque monkeys and rabbits. Other animals are not susceptible to the virus.

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Pathogenesis and symptoms of rubella

The virus, which enters the human body by airborne droplets, first multiplies in the cervical lymph nodes. A week later, viremia develops, and a week later, a rash appears, starting from the face and moving to the trunk and limbs. During this period, fever, enlargement of other regional lymph nodes, and joint pain (especially in adults) are possible. The rash usually lasts 2-3 days.

While rubella in children usually occurs benignly, as a mild disease, in adults the course of the disease is quite severe, sometimes arthritis, encephalitis and thrombocytopenia develop. Rubella is especially dangerous for women of childbearing age, as it can cause congenital rubella syndrome (CRS), caused by the ability of the virus to penetrate the placenta during viremia and have a teratogenic effect on the growing fetus. This is due to the cytopathic effect of the virus on both dividing cells of the fetus and on the cells of the placental vessels. This can result in heart defects, deafness, congenital diseases of the organs of vision, microcephaly, spontaneous abortion, stillbirth, etc.

Immunity

Virus-neutralizing antibodies (IgM) appear in the blood during the period of rash manifestation, their titer reaches its maximum after 2-3 weeks, and after 2-3 months they disappear. IgG appear after the rash disappears and persist for a long time. Immunity after rubella suffered in childhood is lifelong.

Epidemiology of rubella

Rubella is a typical anthroponous airborne infection, highly contagious for individuals without immunity. The peak incidence of rubella usually occurs in the spring. In the 20th century, epidemics were observed every 6-9 years, and after each epidemic, the incidence decreased over the next 5 years, and then increased again to the epidemic level 6-9 years after the last major outbreak. With rubella, the virus is excreted from the mucus of the nasopharynx and upper respiratory tract 1-2 weeks before the rash appears and for 2-3 weeks after the onset of the rash. In children infected in utero, the virus can be excreted in the urine and feces for 1-1.5 years.

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Laboratory diagnostics of rubella

Rubella can be diagnosed using virological and serological methods. The material for isolating the virus is nasopharyngeal secretions (in the presence of catarrhal phenomena) and blood before the rash appears; blood, urine, and feces are used after the rash appears. The material is used to infect cell cultures, and the virus is identified in the RTGA assay, as well as by the interference test. In case of congenital rubella, urine and feces of children are used as material for testing.

Serological diagnostics of rubella determines IgM and IgG antibodies to the rubella virus in the blood using RIF, IFM, RIM. Paired sera are used, and the increase in antibody titer is determined.

Specific prevention and treatment of rubella

The main thing in the prevention of rubella is quarantine measures in children's groups. Selective immunization of girls aged 12-14, young women and women of childbearing age is advisable. For these purposes, live and killed vaccines are used, obtained from attenuated strains of the virus, passaged at low temperature in the culture of kidney cells of green monkeys and diploid cells of the lungs of human embryos. There are associated drugs in combination with vaccines against measles and epidemic mumps. WHO has set the task of reducing the incidence of congenital rubella syndrome by 2010 to a level below 1 per 100,000 live births. As already indicated, a live trivalent vaccine is used for mass vaccination against measles, mumps and rubella.

There is no specific treatment for rubella.