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Two New Recombination Sequences Found in Norovirus Genus
Previous research has found that on the basis of sequence variation, there are at least three genogroups of Norovirus. Furthermore, studies have indicated that there is within genogroup recombination that is able to give rise to hybrid strains that can cause outbreaks in humans. The present study used Recombination Analysis Tool (RAT) in order to detect recombination in several strains of Norovirus. Statistical analysis revealed two novel recombinants. The recombination break point was found between ORF1 and ORF2 which is of note since this is true for the majority of norovirus recombinants. These findings further support the idea that the region at the end of ORF1 and ORF2 is a “hot spot” for genetic recombination. It is also of note that the researchers found that recombinant Noroviruses share sequences with isolates from geographically distinct regions; for example, a California strain was found to have parental origins in Hawaii and the UK.
Etherington, G. J., Dicks, J., Roberts, I. N., 2005. High throughput sequence analysis reveals hitherto unreported recombination in the genus Norovirus. Virology.
New Method for Detecting Norovirus in Stool Samples
The accurate detection of the presence of norovirus is incredibly important for analysis of the transmission and incidence of the virus. Unfortunately, the high genetic polymorphism of noroviruses makes detection of the virus using PCR difficult. The current detection technique is RT-PCR which uses generic primers and Southern hybridization of the PCR products. However, this method is time-consuming and not very cost-effective when examining large numbers of samples as is the case during epidemics. The current study developed a nested RT-PCR assay that is sensitive and reactive to the different strains of norovirus. This will be an important tool for future epidemiological research about norovirus.
Medici, M.C., Martinelli, M., Ruggeri, F.M., Abelli, L.A., Bosco, S. Arcangeletti, M.C., Pinardi, F, De Conto, F., Calderaro, A. Chezzi, C. Dettori, G. 2005. Broadly reactive nested reverse transcription-PCR using an internal RNA standard control for detection of noroviruses in stool samples. J Clin Microbiol. 43(8):3772-8.
Replication of Norwalk RNA in Cultured Cells
Previous research of noroviruses has been severely limited because it is difficult to culture the cells and an accurate animal model of infection does not exist. The present study was able to achieve replication of Norwalk virus RNA and its packaging into viral particles in mammalian cells. The basis of this system was driving the expression of the NV viral RNA in the cell cytoplasm by T7 RNA Pol produced by the recombinant vaccinia virus strain MVA.
Asanka, M, Atmar, R.L., Ruvolo, V., Crawford, S. E., Neill, F. H., Estes, M. K. 2005. Replication and packaging of Norwalk virus RNA in cultured mammalian cells. Proc Natl Acad Sci USA. 102(29):10327-32.