Laboratory Diagnosis of Measles virus
المؤلف:
Baijayantimala Mishra
المصدر:
Textbook of Medical Virology
الجزء والصفحة:
2nd Edition , p184-185
2025-10-22
65
The clinical presentations of measles are usually classical in nature. The laboratory confirmation is required in cases that are clinically challenging such as immunocompromised or individuals with pre-existing antibodies, or to confirm a suspected outbreak particularly in low or non-endemic countries (Flowchart 1).
Fig1. Lab diagnosis of measles
Serology: Measles specific IgM antibody detection is the mainstay of confirmation of disease. Measles IgM appears around 4 days after the onset of rash. Therefore, it may be negative during the first few days of illness. Two-thirds (75%) of cases become positive by 3rd day of rash and almost all by 4th day of rash. It persists for 3–4 weeks and starts to decline by 4th week of illness and becomes non-detectable by 8th week.
Demonstration of four-fold rise in titer can be employed by detection of antibody in acute and convalescent serum collected at a gap of 10–30 days. This can be done by: IgG antibody by ELISA, hemagglutinating antibody by HAI assay.
Detection of measles specific IgG antibody or HAI antibody in a single serum sample indicates past infection and is used for serosurveillance study.
Virus isolation: Measles virus can be isolated from several clinical samples using susceptible cell line. Respiratory samples, such as nasal or throat swabs, nasopharyngeal aspirate, urine and blood samples can be collected for isolation of virus and for detection of RNA. Swabs should be collected in viral transport medium and transported in cold chain (4°C) to the lab. It can be stored at 4°C for a few hours then should be stored at –70°C. Samples for virus isolation should be collected as soon as possible after the onset of rash.
Urine collection: First morning urine is ideal to collect. Preferably around 50 mL should be collected. Immediately sample should be centrifuged at 4°C at 1500 rpm for 5–10 minutes. The deposit is transferred to 1–2 mL of VTM and then stored at –70°C.
Blood: Lymphocytes act as the source of measles virus. Blood is collected in heparinized vial, lymphocytes are separated using Ficoll hypaque gradient centrifugation technique. The purified lymphocytes are stored at –70°C.
Cell lines: B95a and Vero/SLAM are the two cell lines recommended for isolation of measles virus from clinical samples.
B95a: This is an Epstein-Barr virus transformed marmoset B lymphoblastoid cell line. These cells are 1000 times more sensitive than commonly used cell lines. Hence, one of the recommended cell lines for primary isolation of measles virus. The cell line is easy to maintain and cytopathic effect produced by measles virus is readily observed. However, as the cells are Epstein-Barr virus infected, these cells should be handled as infectious material. Hence, not preferred currently in measles virus laboratory network.
Vero/SLAM: This cell line is made up of Vero cells transfected with plasmid encoding genes of human signalling lymphocyte activation molecule (SLAM) also called CDw150. This is a glycoprotein present on the membrane of some of the T and B cells and act as the receptor for binding of measles virus. SLAM acts as a receptor for both wild type and vaccine strains. The sensitivity of Vero/SLAM for isolation of measles virus is same as that of B95a cells. These cells are also sensitive to laboratory adapted measles virus strains, vaccine strains and rubella virus. They possess less biological hazard than B95a cells. The disadvantage of Vero/SLAM is the requirement of Geneticin for expression of SLAM. This cell line is currently used for isolation by the WHO measles virus laboratory network.
Cytopathic effect: Measles virus produces two types of cytopathic effect (CPE). First, multi nucleated syncytial giant cell (Warthin Finkeldey cell) due to fusion of the infected cells induced by the virus. Multinucleated giant cells are formed by the wild virus. Second, spindle cells or stellate cells are produced by the adapted measles virus (strain that has been given repeated passage in the cell line).
Identification from infected cell can be made by (i) hemadsorption using 0.5% monkey RBC, (ii) immunofluorescence using measles virus specific antibody or (iii) by reverse transcriptase PCR using specific primers. Infected cells can also be stained for demonstration of intranuclear and intra cytoplasmic inclusion bodies.
Reverse transcriptase polymerase chain reaction (RT-PCR): This is used for genetic characterization of the isolated strains rather than as a diagnostic procedure.
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