Efficient isolation of mumps virus from a community outbreak using the marmoset lymphoblastoid cell line B95a

The incidence of mumps infection in the UK was reduced greatly by vaccination as a component of MMR vaccine, but cases and outbreaks continue to occur. Although in specialised laboratories RT-PCR is available for detection of mumps virus RNA in clinical samples, in routine laboratories virus isolation remains a standard method for diagnosing mumps virus infection. Furthermore, isolation of mumps virus strains circulating currently is important for monitoring the ability of vaccine-induced antibody to neutralise any genotypes recognised recently and to detect any changes in phenotype. In this study we compared rhesus monkey kidney (RMK) cells with the cell line B95a for mumps virus isolation from twenty throat swabs collected during a mumps outbreak in a religious community with low MMR coverage. Mumps virus was isolated from eight cases (40%), six were positive in both cell cultures and two in only one, all positive samples being collected within 2 days of onset. Virus growth in B95a cells was detected by the production of a syncytial cytopathic effect, and confirmed by an indirect fluorescent antibody test using a mumps monoclonal antibody. The B95a cell line was found to be equally as sensitive for mumps isolation as RMK cells, which are regarded as the 'gold standard', thus providing an alternative to the use of primary animal cell culture.