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Rubella - Causes and Pathogenesis
Medical expert of the article
Last reviewed: 04.07.2025
Causes of rubella
The cause of rubella is the rubella virion, spherical in shape, 60-70 nm in diameter, consisting of an outer membrane and a nucleocapsid. The genome is formed by a non-segmented +RNA molecule. The virion is antigenically homogeneous.
Rubella virus is sensitive to chemical agents. It is inactivated by ether, chloroform, formalin. At a temperature of 56 °C it dies after 30 minutes, at 100 °C - after 2 minutes, when exposed to ultraviolet radiation - after 30 seconds. In the presence of protein in the environment, the resistance of the virus increases. At low temperatures, the virus retains biological activity well. The optimal pH for the virus is 6.8-8.1.
The virus contains V- and S-soluble antigens that exhibit complement-fixing activity.
Rubella virus can multiply in many types of primary and continuous tissue cultures of humans, monkeys, rabbits, bulls, and birds.
Virions are formed in the cytoplasm of a sensitive cell. The virus has a weak cytopathogenic effect and tends to form a chronic infection.
Reproduction of the rubella virus in tissue environments is accompanied by the formation of interferon.
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Pathogenesis of rubella
The site of primary replication of the virus is unknown, but viremia develops already during the incubation period. and the virus is released into the environment with exhaled aerosol, urine and feces. The virus enters the body through the mucous membranes of the upper respiratory tract. Subsequently, the virus multiplies in the lymph nodes (this process is accompanied by polyadenopathy), as well as in the epithelium of the skin, leading to the appearance of a rash. The virus penetrates the BBB and placenta. As a result of the activation of interferon production, the formation of cellular and humoral immunity, the circulation of the virus stops, and recovery occurs. However, in pregnant women and children with congenital rubella, the virus can exist in the body for a long time.
In congenital rubella, the virus enters the fetus through the mother's bloodstream and infects the epithelium of the chorionic villi and the endothelium of the placental blood vessels. Then it enters the fetal bloodstream. In this case, organs and tissues that are in the process of formation, i.e. in the so-called critical period of intrauterine development, are affected (for the brain, this is the 3rd-11th week of pregnancy, for the eyes and heart - the 4th-7th, for the organ of hearing - the 7th-12th week). Psychomotor disorders of the fetus develop when the mother gets rubella in the 3rd-4th month of pregnancy. The formed fetus is relatively resistant to the virus. The frequency of fetal damage depends on the gestational age. Rubella infection in the 1st-4th week of pregnancy leads to fetal damage in 60% of cases, in the 9th-12th week - in 15% of cases, in the 13th-16th week - in 7% of cases. The earlier the fetus is infected, the more severe and diverse its lesions are. The development of fetal defects and anomalies is based on the ability of the virus to suppress the mitotic activity of cells and, to a lesser extent, its direct cytopathological effect.
Epidemiology of rubella
The source of the rubella pathogen is patients, including those with an erased and atypical course of the disease, persons with asymptomatic infection and virus carriers. The virus is excreted from the mucus of the upper respiratory tract 1-2 weeks before the rash appears and for 3 weeks after the rash. In children with congenital rubella, the pathogen can be excreted from the body with urine, sputum, feces up to 2 years after birth.
The main route of transmission of the pathogen is airborne. Viremia developing with rubella causes intrauterine transmission from mother to fetus, as well as the probability of parenteral transmission of the pathogen. The spread of the pathogen through care items has no practical significance.
Susceptibility to rubella is high. Children in the first six months of life are immune to the infection if the mother has immunity to this infection. Children aged 1 to 9 years are most susceptible to rubella, most of whom do not have immunity against rubella.
Post-infection immunity to rubella is lifelong in most cases; recurrent cases of the disease are extremely rare.
Rubella has different forms of epidemic process. Large cities are characterized by constant morbidity with seasonal winter-spring increases. There may be epidemic outbreaks, usually occurring at intervals of 7 years.
Rubella incidence is characterized by a pronounced focality in children's groups. Rubella spreads where people are in long-term and close contact (family, school, kindergarten, hospital).