HUMAN ENTERIC CALICIVIRIDAE - A NEW PREVALENT SMALL ROUND-STRUCTURED VIRUS GROUP DEFINED BY RNA-DEPENDENT RNA-POLYMERASE AND CAPSID DIVERSITY

Sequence comparison of the RNA-dependent RNA polymerases of small roun d-structured viruses (SRSVs) from 10 recent U.K. outbreaks of gastroen teritis revealed significant genetic variation. Computer analyses indi cated that these viruses can be divided into two discrete groups. SRSV group I contains the previously characterized antigenic type 1 Norwal k and type 3 Southampton viruses. The amino acid sequences of the RNA polymerase, capsid and ORF3 of these two viruses are relatively simila r (about 92%, 69% and 72% amino acid identity, respectively). A repres entative member of group II SRSVs, Bristol virus, was subjected to a d etailed genetic analysis. Bristol virus is a recent antigenic type 2 i solate from a U.K. hospital outbreak of gastroenteritis. Using a singl e clinical sample the 3'-terminal 3881 nucleotide cDNA sequence [exclu ding the poly(A) tail] of this virus was determined. Analysis of the s equence revealed significant differences from those of group I viruses with the RNA polymerase region, capsid and ORF3 showing only about 62 %, 43% and 30% amino acid identity respectively with the equivalent pr oteins of the Norwalk and Southampton viruses. These data suggest that the morphologically identical SRSVs belong to at least two geneticall y distinct groups.