Norwalk-Like Viruses, A Common Cause of Sporadic Acute Gastroenteritis in korean Children

ABSTRACT

Norwalk-like virus (NLV), one of the emerging enteric pathogens in sporadic cases and outbreaks of acute gastroenteritis (AG) worldwide, are 30-35 nm in diameter and have a single stranded RNA genome, size 7.6 kb. As genomic sequence data from several isolates of NLVs are being reported, the genetic relationships among these viruses are now being described. Based on the level of sequence similarity in the RNA polymerase region of NLVs, at least three genogroups can be defined the Norwalk virus (NV)-, the Snow Mountain agent (SMA)-, and the Sapporo-genogroups. A high prevalence of serum antibody to NV-related viruses but no antigenpositve stools (either observed to contain the NLV by immune electron microscopy or suspected of containing the NLV) has suggested that genomically different NLVs are present among Korean children. The purpose of our work therefore was to detect NLVs from Korean infants and children with AG and to characterize the partial genome (RNA-dependent RNA polymerase region) of currently circulating Korean isolates. The cDNA fragments of 110 to 470 bp corresponding to the RNA polymerase region were generated by reverase transcription-polymerase chain reaction (RT-PCR) using three primer pairs (36/35, 36/51, or 36/101) derived from the prototype NV (8FIIaNV/68/US). Of 279 stool samples tested, 25 (9%) specimens were positive by RT-PCR and the amplified productscontained GLPSG and YGDD amino acid motifs, characteristic of positive-strand RNA-dependent RNA polymerases, at the predicted distance from the primers. In 6% of the infectious episodes with diarrhea, NLVs appeared to be the sole pathogen. Double infections occurred mainly with rotavirus and triple infections occured with both rotavirus and adenovirus or with both rotavirus and astrovirus. This study indicates that NLVs are a common cause of sporadic AG in Korean infants.