Rubella virus exclusively affects humans and causes rubella in them. This childhood disease is highly contagious, but leads to lifelong immunity with its onset. Rubella virus (also known as German measles virus) causes characteristic red skin spots (exanthema) on the face and upper body, as well as fever and swelling of the lymph nodes if necessary. The pathogen is widespread worldwide. However, in countries with a high vaccination rate of more than 90 percent of all children (such as Germany), the disease hardly ever occurs. However, the rubella virus is dangerous in case of infection during pregnancy. Here, rubella embryofetopathy can lead to severe malformations of the child as well as miscarriages. Worldwide, the annual number of children born with rubella embryofetopathy is estimated at about 100,000.
What is rubella virus?
Rubella viruses belong to the genus Rubivirus. They are the only representative there. Their family is the Togaviridae (togaviruses), whose genome is typically a single-stranded RNA of positive polarity. The genome is encased in a twenty-sheet (icosahedral) capsid. The three structural proteins of Rubella virus are formed by the capsid protein and the two envelope proteins (E1 and E2). The virus particles of togaviruses have a spherical shape. They are protected from the outside by a lipid membrane, the viral envelope. The structure of the viral surface is uniform. Therefore, there is only this one serotype of rubiviruses. The pathogens are passed on by droplet infection. Scientists state the contagiousness of the rubella viruses as medium (50 percent). The viruses preferentially attack the mucous membranes of the upper respiratory tract and penetrate the body there. The first major multiplication occurs in the lymphatic tissue. The viruses are then released into the bloodstream. During the critical phase of pregnancy, the virus can now reach the unborn child via the placenta. The incubation period basically lasts two to three calendar weeks. The infected person is considered to be infected one week before and after the first reddening of the skin. When the incubation period is over, red spots (efflorescences) usually appear on the face and often behind the ears, which are initially still isolated. Later they spread to the upper body and extremities. Two to three days later, these spots disappear. Parallel to this course of the disease, fever of up to about 39 °C sets in. In addition, there may be complaints in the upper respiratory tract, conjunctivitis, headache and pain in the limbs, as well as swelling of the lymph nodes on the head. The symptoms caused by the rubella virus can easily be confused with other diseases that also cause fever and rashes. These include three-day fever, measles and scarlet fever. In about 50 percent of cases of rubella, the typical symptoms do not appear. In addition, the detection of rubella viruses is possible only in relatively complex procedures, about whose significance from a medical point of view, there are still major differences of opinion.
Occurrence, distribution, and characteristics
Like all togaviruses, Rubella attaches to the cell surface via certain specific receptors. A so-called endosome vesicle is formed, which attracts the viral bodies. If the pH outside the cell is in the neutral range, the E1 protein is surrounded by an E2 envelope protein. Then, inside the endosome, at acidic pH, the outer sections of the E1 protein come to expose. All necessary preparations for fusion between the endosomal membrane and the viral envelope are made. Finally, the capsid disintegrates and the genome can be released. The complicated molecular replication of the virus can begin. So far, science has not been able to clearly identify the chemical principle by which rubella embryofetopathy works during pregnancy. Certain experiments suggest that the rubella virus may have a killing effect on specific cell types. This is what makes rubella infection during pregnancy so particularly risky. During the first eight weeks, export of the rubella virus to the mother’s abdomen very often results in embryo impairment. In extreme situations, miscarriage can occur. Dangerous premature births also occur repeatedly.
Diseases and ailments
As a result of infection of the unborn child, a wide variety of malformations can be realized. Here, for example, heart defects, lens opacities of the eyes and hearing loss in the inner ear occur. These serious consequences are caused by infections in the early stages of pregnancy (around the fourth week). As the pregnancy progresses, the potential consequences of rubella infection weaken. Consequences such as decreased platelets, liver and heart muscle inflammation, decreased head circumference, and reduced body weight at birth may be considered. Infants with congenital rubella infection should be isolated as much as possible during the first six months of life. In them, special tests are regularly performed in nasopharyngeal secretions and also in urine for safety reasons. In the hospital setting, patients with rubella are always isolated. In contrast, exclusion of persons with rubella in community settings is not mandatory. However, the disease is generally notifiable. A special vaccination with immunoglobulins is available for pregnant women, but this should be administered within three days of suspected contact with ill or infected persons. However, the vaccination cannot reliably protect against infection. An antibody test for rubella virus allows specific measures to be taken to prevent subsequent harm to the baby.
