Rubella Virus

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A Viral Biorealm page on the Rubella Virus

Classification

Viruses; ssRNA viruses; ssRNA (+) viruses; Togavirdae; Rubivirus; Rubella Virus [NCBI]

Description and significance

The only member of the Rubivirus genus, Rubella Virus is only known to infect humans [5] and is responsible for the common childhood disease known as German Measles or Three Day Measles.[3] The disease presents primarily as a skin rash with other mild symptoms in adults who contract the disease. [1] Rubella can also cause arthritic symptoms, most commonly in women [5] Rubella Virus can be prevented with the MMR (Measles, Mumps, Rubella) Vaccine which makes the virus uncommon in countries where vaccines are available. [7] Rubella Virus can cause serious harm to unborn fetuses of mothers who contract Rubella Virus within the first trimester. The virus causes CRS (Congenital Rubella Syndrome) causing birth defects. CRS can cause a variety of birth defects and can lead to miscarraige or stillbirth. [5]

Genome structure

The Rubella Virus genome is composed of 9757 nucleotides and has similar genomic structure to other Togaviruses. The Rubella Virus has the highest concentration of G/C nucleotides of any RNA virus with 69.5% of the genome consisting of those nucleotides. [4] Rubella has been sequenced completely for three strains shwoing >95% homology between the three strains. [5]

Cell structure & life cycle

Rubella Virus is an enveloped virus, circular or oval in shape and 60nm in diameter. The virion is composed of a capsid core containing a single copy of genomic RNA. The outer membrane is a lipid bilayer containing specialized glycoproteins (E1 and E2) believed to be responsible for attachment to host cells. It is also believed that a pH of 6.0 or less induces conformational changes in the glycoproteins making attachment of the viral envelope to host cells more likely. Rubella virus likely enters cells via endocytosis. Once in the cell a conformational change occurs in the capsid shell releasing the genetic information into the cell. Replication is slow with a latency period of 8-12 hours, with structural proteins appearing at 12-16 hours and peak viral 36-48 hours after infection. In volunteer subjects infected via aerosol the characteristic rash typically appears 16-20 days from the time of exposure. [5]

Pathogenesis

If it is a pathogen, how does this organism cause disease? Human, animal, plant hosts? Describe virulence factors and patient symptoms. Rubella virus only infects humans and is spread from person to person through contact or from a cough or sneeze as the rubella virus lives in the mucus of an infected person. The virus can be transmitted up to a week before the rash appears and one to two weeks after. [1] Rubella is also transmitted from an infected mother to her unborn child causing CRS. [1] Symptoms for postnatal Rubella virus include a rash spreading down from the face to the extremities and in some cases a runny nose, fever or joint pain. It is possible for the virus to be asymptomatic. [5] CRS causes a number of birth defects which include but are not limited to prenatal cataracts, deafness, low birth weight and mental retardation. [2] Rubella virus only has a large risk of infection if the disease is contracted by the mother in the first trimester, after which birth defects are less likely. [5] There is no known treatment for Rubella.

Rubella Vaccination

Included as a part of the common childhood vaccination known as MMR (Measles, Mumps, Rubella) vaccination. The Meruvax II or Rubella vaccination effectively prevents the disease after a single injection in humans 12 moths or older. While antibodies are usually developed after a single infection of the virus the vaccine is vital to prevent infection of expecting mothers who could pass on the virus to their unborn fetus. The vaccine is a freeze dried sample of the Wistar RA 27/3 strain of Rubella virus which when injected induces an immunity by causing a modified rubella infection. Rubella hemagglutinin antibodies are produced to prevent infection of wild rubella virus. [6] The vaccination MMR is a required vaccination in most states for children wishing to enter school. [1] It is not yet clearly known if the immunity is permanent but it is known to last at least 10 years. [6]

References

[1] A.D.A.M Medical Encyclopedia, "Rubella". PubMed Health, 2011

[2] A.D.A.M Medical Encyclopedia "Congenital Rubella". New York Times: Health Guide, 2011

[3] CDC, "Rubella homepage" CDC.gov 2009

[4] Dominguez G., Wang C., Frey T. "Sequence of the genome RNA of rubella virus: Evidence for genetic rearrangement during togavirus evolution" Virology Vol 177, Issue 1, July 1990, p. 225

[5] Lee J., Bowden S. "Rubella Virus Replication and Links to Teratogenicity" Clinical Microbiology Reviews, 2000, Vol. 13, No. 4, p. 571-587

[6] Merck Sharp & Dohme Corp., "M-M-R II Vaccine Live package insert" Merk & Co., Inc. 2010

[7] Kaneshiro N, "MMR vaccine". Medline Plus NIH, 2010