Morphology of rubella virus

Molecular biology of rubella virus

This chapter summarizes the present medical significance of rubella virus. Rubella virus infection is systemic in nature and the accompanying symptoms are generally benign, the most pronounced being a mild rash of short duration. The most common complication of rubella virus infection is transient joint involvement such as polyarthralgia and arthritis. The primary health impact of rubella virus is that it is a teratogenic agent. The vaccination strategy is aimed at elimination of rubella and includes both universal vaccination of infants at 15 months of age with the trivalent measles, mumps, rubella (MMR) vaccine and specific targeting with the rubella vaccine of seronegative women planning pregnancy and seronegative adults who could come in contact with women of childbearing age, although it is recommended that any individual over the age of 12 months without evidence of natural infection or vaccination be vaccinated. Medically, the current challenge posed by rubella virus is to achieve complete vaccination coverage to prevent resurgences.

Fatty acid composition of rubella virus and BHK21/13S infected cells

The rubella virus is composed of RNA (2.4 per cent dry weight of the virus), proteins (74.8 per cent), carbohydrates (4:2.5 per cent of which are present as aminosugars, 1.5 per cent as neutral sugars) and lipids (18.8 per cent). The analysis of fatty acids in rubella virus was done at the same time as the analysis of control cells and infected cells. In the virus, the main fatty acids are: palmitic (26 per cent), stearic (15 per cent), oleic (15 per cent). Rubella virus differs from other togaviruses by the presence of fatty acids with odd-numbers of atoms of C (C15, C17, C19) which represent 23 per cent of total acids and of an hydroxyacid. In the cells, the acids oleic, palmitic, stearic and linoleic represent 90 per cent of total fatty acids. The infection of the BHK21/13S cells by rubella virus leads essentially to an increase (35 per cent) of the amount of linoleic acid with a decrease of palmitic and oleic acids.

Lipids in Viruses

This chapter discusses lipids in viruses. Lipid forms an integral part of many viruses and exists either in the form of a continuous envelope or in lipoprotein complexes that surround a nucleoprotein core or helix. In general, the envelope can be described as a molecular container for the genetic material of the virus. Viruses are obligate intracellular parasites and are not known to carry genetic coding for enzymes involved in lipid synthesis. Hence, they generally contain the same classes of lipid as are found in the host cell or their membrane of assembly. Lipids make up 20–35% by weight of most viruses; however, there are exceptions such as vaccinia virus, which has only 5% lipid despite having a complex multimembrane envelope structure. Naked herpesvirus capsids closely resemble non-lipid-containing viruses such as adenovirus or polyoma virus, which are also assembled in the nucleus but show full infectivity without any envelope. Both naked and enveloped herpesvirus particles are found in infected cells; however, only enveloped particles are found in extracellular fluids.

Micromorphological aspects of the development of rubella virus in BHK-21 cells

Sequential effects of rubella virus infection in BHK-21 cells were studied by electron microscopy of thin sections of control and infected cells, 2 to 7 days after infection. Vacuolization of cytoplasm in Golgi areas apparently preceded budding of virions from vacuole membranes and involvement of the endoplasmic reticulum. Newly formed endoplasmic reticulum cisternae encircled and segregated virionforming vacuoles together with other cellular elements. Large vacuolar complexes with numerous virus particles developed, and virus release from these areas occurred with disruption at the cell periphery. The viral particles, with a mean diameter of about 56 nm, consisted of an electron-dense core surrounded by a less dense capsid, enveloped by a typical unit membrane derived from the vacuole membrane.