RTPCR See polymerase chain reaction

R-type virus particles ('R' because of the structures radiating from the core). Enveloped virus particles 100nm in diameter with a clear space between the central core and outer envelope. Across this space are radial threads. First described in BHK21 cells, and later in calf kidney cells and hamster tumors induced by polyoma, SV40, Rous sarcoma and mouse sarcoma viruses. They are usually seen singly or in small groups within cell vacuoles. They have reverse transcriptase and can rescue mouse sarcoma virus from non-producer cells. No known pathological role.

Albu E and Holmes KV (1973) J Virol 12, 1164 Bergman DC et al (1977) J Natl Cancer Inst 58, 295

Rubarth's disease virus Synonym for Canine adenovirus.

Rubella virus (RUBV) The type species of the genus Rubivirus. The virus is 50-70nm in diameter, has a triple-layered envelope 8nm thick surrounding an electron-lucent layer 11nm thick and an electron-dense core 30nm in diameter. Matures by budding from cytoplasmic membranes. The nucleic acid is positive single-stranded RNA 9757 nt in length, with an additional 3' poly A tract. There are three structural proteins: two glyco-proteins (E1 and E2) and a capsid protein, C. The gene order in the precursor polyprotein is NH2-CP-E2-E1-COOH. Infectivity sensitive to lipid solvents and pH 3. Day-old chick erythrocytes are agglutinated at 4°C. No antigenic differences have been observed between strains. Replication occurs in duck eggs and a wide variety of cell cultures, in which it may be demonstrated by interference with growth of another virus, by CPE or by immunofluorescence. For isolation, primary African green monkey kidney cell cultures or BHK21 cells are best. Causes a mild illness in humans with generalized rash and enlarged lymph nodes. Usually little fever or constitutional disturbance. Incubation period 16-18 days. Meningoencephalitis and other complications are rare but infection during the first 3-4 months of pregnancy often results in infection of the fetus and congenital abnormalities such as cataract, hearing loss, cardiac and dental malformations and microcephaly. Congenitally infected children have Rubella virus antibodies but continue to excrete virus for many months. A very few cases of progressive rubella panencephalitis have occurred, commencing in the second decade of life and slowly progressing. Monkeys, rabbits, hamsters, guinea pigs, rats and mice can be infected experimentally, but show no disease except leukopenia and rash in some rhesus monkeys, and growth retardation in congenitally infected animals. Major epidemics occur every 9-10 years and 80-90% of young adults have antibodies. Several excellent live attenuated vaccines have been developed; the RA27/3 strain is used most widely. Rubella vaccine is normally given as a component of measles-mumps-rubella (MMR) vaccine to all preschool children at about 12-15 months of age. A booster should be given to all girls at the age of 12-l4 years, if they were not immunized at 12-15 months. Synonym: German measles virus.

Best JM (1991) Epidemiol Infect 107, 17 Frey TK (1994) Adv Virus Res 44, 69 Pugachev KV et al (1997) Arch Virol 142, 1165 Reef SE (1999) MMWR 48 (Suppl), 199

rubeola virus Synonym for Measles virus.

Rubivirus A genus of the family Togaviridae. Antigenically unrelated to viruses in other genera of the family. Rubella virus is the only species in this genus, and the structural proteins have no amino acid similarity to those of alphaviruses.

Rubulavirus A genus in the family

Paramyxoviridae. Mumps virus is the type species.

'rule of six' A phenomenon discovered by Calain and Roux whilst investigating the replication of deletion mutants of Sendai virus. Efficient genome replication only occurred when the total length of the genome was a number of bases divisible by six. It is believed to result from the notion that the NP protein of paramyx-oviruses covers precisely six nucleotides when binding to the RNA. The phenomenon has stood the test of time as new paramyxoviruses have been discovered and sequenced. For example, the two most recently sequenced paramyxoviruses follow this rule: the Hendra virus genome has 18 234 nt and Nipah virus has 18 246 nt.

Calain P and Roux L (1993) J Virol 67, 4822 Peeters BPH (2000) Arch Virol 145, 1829

Runde virus A possible species in the genus Coronavirus. An arbovirus isolated from the tick, Ixodes uriae, collected in sea bird colonies at Runde, Norway. No antigenic relationship to avian infectious bronchitis virus or to major arbovirus groups. Lethal to newborn mice but in 2-week-old mice produces a persistent infection and chronic disease may result. Antibodies fail to neutralize virus infectivity completely. Replicates with CPE in BHK21 cells. Hemagglutinates chicken erythrocytes. Antibodies are present in sea birds. Not reported to cause disease in humans.

Traavik T (1979) Acta Pathol Microbiol Scand B 87, 1

Traavik T and Brunvold E (1978) Acta Pathol Microbiol Scand B 86, 349

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