Test performed on weekdays
Rubella virus is a ss RNA virus classified as a rubivirus in the family Togaviridae.
Rubella (when symptomatic ? 25-50% infections are aymptomatic) is usually a mild disease characterised by an erythematous maculopapular discrete rash, generalised lymphadenopathy (suboccipital, postauricular and cervical) and slight fever. Transient polyarthralgia is more commonly seen in adults especially females. Rare complications include encephalitis and thrombocytopenia. However, infection during pregnancy (in particular the 1 st trimester) will result in the newborn having features (one or several) of the congenital rubella syndrome [CRS] (see below):
* Opthalmologic abnormalities (cataracts and retinopathy)
* Cardiac abnormalities (patent ductus arteriosus, pulmonary artery stenosis)
* Auditory abnormalities (sensorineural deafness)
* Neurologic abnormalities (behavioural disorders, meningoencephalitis, mental retardation).
In addition, infants with CRS are frequently growth retarded, have radiolucent bone disease, hepatosplenomegaly, thrombocytopenia and purple skin lesions. Severity of disease lessens with increasing gestational age at time of infection. CRS is a direct result of rubella virus interfering with the timing of developmental processes in the foetus.
Postnatal rubella is transmitted through direct or droplet contact from nasopharyngeal secretions. Peak incidence of infections occur in late winter and early spring.
The average incubation period of rubella is 16-18 days (range 14-21 days), with the maximal risk of communicability occurring from a few days before to 7 days after rash onset.
A number of methods have been used to determine rubella immune status and/or infection including haemolysis in gel (SRH), latex agglutination and haemagglutination inhibition (HAI). More recently, rubella specific IgG and IgM EIA techniques are the methods of choice. Rubella virus can be isolated from nasal specimens by inoculating into a rabbit kidney (RK 13) cell line. This line will produce visible CPE.
The vaccine for rubella is a live attenuated type presented most commonly in the trivalent MMR form. Vaccine given after exposure does not prevent illness, however immunisation of exposed non-pregnant individuals may be appropriate. The following adverse reactions have been reported:
* Five to fifteen percent of children develop fever 5-12 days after vaccination. Rash occurs in approximately 5% of vaccinees. Lymphadenopathy occurs less commonly.
* Joint pain (usually in small peripheral joints) has been reported in approximately 0.5% of children. Arthralgia is more common in postpubertal females occurring 7-21 days after vaccination in 10-20% of recipients.
Contraindications for administration of rubella vaccine are:
* The vaccine must not be given to pregnant females. Inadvertent administration of vaccine in the first trimester results in a theoretic risk of 1.6% to the foetus developing CRS.
* Children with serious febrile illnesses should not be vaccinated until recovery is complete.
* Vaccine should not be given in the 2 weeks before or the 3 months after the administration of immunoglobulin or blood transfusion because of the possibility that antibody will neutralise the vaccine virus and prevent successful immunisation.
* Patients with immunodeficiency diseases and those receiving immunosuppressive therapy should not receive rubella vaccine.
Detection of rubella specific IgG at a level greater than or equal to 10 IU/mL is consistent with immunity. Despite this, re-infection can occur in situations of prolonged close contact where antibody levels are low.
Generally, immunity gained from exposure to wild type virus is more prolonged than that gained through vaccination. Also, there have been numerous reports of individuals unable to be successfully immunised who then become infected with the wild type strain and mount a strong and prolonged immune response.
References
1. Abbott Laboratories Axsym Rubella IgG product insert.
2. 1997 Red Book. Report of the Committee on Infectious Diseases. 24 th Edition. American Association of Paediatrics p ixxvi, 1-764. 1997.
For further information contact the laboratory (contact via Lablink: 22000 or (09) 307-8995 or 0800 522 7587) ,or:
the Virology team
virology@adhb.govt.nz