NORWALK-LIKE VIRUSES - DEMONSTRATION OF GENOMIC DIVERSITY BY POLYMERASE CHAIN-REACTION

A reverse transcription-polymerase chain reaction (RT-PCR) amplificati on procedure was developed for the detection of Norwalk-like viruses i n fecal specimens. Ninety-nine fecal specimens collected in the United Kingdom and containing small round-structured virus particles as dete rmined by electron microscopy were tested. They came from 50 outbreaks and 16 sporadic cases of viral gastroenteritis. RT-PCR products of th e appropriate size for Norwalk virus RNA were detected in 15 specimens from three outbreaks, suggesting that viruses closely related to Norw alk virus have not been circulating widely in the United Kingdom in re cent years. From four isolates, the RT-PCR amplification products of t wo genomic regions were sequenced and the degree of genomic variation was compared. DNA sequencing of the PCR products revealed strong simil arities among strains from the United Kingdom (approximately 97% for b oth regions amplified) but significant differences from Norwalk virus (67 to 78%). All of the viruses detected by RT-PCR were classified as serotype UK2 by solid-phase immune electron microscopy or enzyme-linke d immunosorbent assay. These findings provide evidence of a genomic re lationship between Norwalk virus and serotype UK2 small round-structur ed viruses.