Laboratory Diagnosis of Rubella virus
المؤلف:
Baijayantimala Mishra
المصدر:
Textbook of Medical Virology
الجزء والصفحة:
2nd Edition , p196-197
2025-11-05
56
As the clinical manifestation in rubella is not specific and can mimic many other exanthematous diseases, clinically suspected rubella cases should always be confirmed by laboratory test.
Detection of rubella infection can be made by isolation of virus and detection of viral genome from various clinical samples and detection of rubella specific antibodies in blood.
Serology
Detection of IgM antibody: Rubella specific IgM antibody detection in serum is the mainstay of diagnosis of acute infection. Presence of IgM in single sample indicates acute or recent infection except in individuals vaccinated with rubella vaccine within 8 days to 8 weeks of sample collection and in absence of rubella transmission in the community.
Positive IgM antibody in infants suggests congenital rubella syndrome or congenital rubella infection.
IgM antibody in rubella infection appears at the time of rash and persists for 4–8 weeks. Around 50% cases are positive for IgM at the time of rash, whereas nearly all cases are positive by 5 days of rash. ELISA is the most commonly used serological test for detection of IgM antibody. Most of the commercially available ELISA tests are 80% specific. False positive rubella IgM can occur due to presence of rheumatoid factor, Parvovirus B19 or CMV infection.
Detection of IgG antibody: IgG antibody starts appearing just after IgM but persists lifelong. Acute rubella infection can also be diagnosed by demonstration of fourfold or more rise in rubella specific IgG antibody in acute and convalescent serum samples collected at least at 10 days interval and tested in parallel. The detection of IgG can be done by quantitative ELISA. Detection of IgG antibody in single serum sample indicates past infection and in infants can be due to passive transfer of maternal antibody.
IgG avidity test: During the early phase of primary infection, IgG antibody is of low avidity in nature which becomes stronger with passage of time. Therefore, detection of low avidity IgG antibody is indicative of primary infection and detection of high avidity IgG indicates past infection or previous rubella vaccination. Avidity test is useful in differentiating between primary and secondary infection.
Isolation of Virus
Rubella virus can be isolated from nasopharyngeal secretion, oral fluid, blood, CSF, urine in rubella and CRS cases, of which nasopharyngeal and throat samples are more commonly used. Tissue samples can also be subjected for virus isolation in CRS cases. Virus can be isolated on the day of rash and can be detected up to 10 days.
Vero/hSLAM (human signalling lymphocyte activation molecule) cell line is recommended for isolation of rubella virus by Global Laboratory Network, WHO. This cell line is made up of Vero cells transfected with plasmid encoding genes of human signalling lymphocyte activation molecule (SLAM) also called CDw150. The virus does not produce any cytopathic effect. Identification of virus is done by detection of E1 protein in the infected cell by immunofluorescence method, immunocolorimetric assay or by RT-PCR.
Isolation of rubella virus, however, is not used for routine patient diagnosis. It is useful for epidemiological and research purpose.
RT-PCR
The viral RNA can be detected from various clinical samples as described for isolation of virus. RT-PCR positivity remain up to 10 days. Sequencing of the PCR product is important for molecular typing, helps in differentiating between wild type virus and vaccine virus and also to track the source of infection. Table 1 gives the salient points of lab diagnosis of rubella virus infection.
Table1. Lab diagnosis of rubella
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