Virological, serological, and clinical features of an outbreak of acute gastroenteritis due to recombinant genogroup II norovirus in an infant home

Abstract

Norovirus (NV) is an important cause of acute nonbacterial gastroenteritis worldwide. Recently, several sporadic cases due to naturally occurring recombinant NVs have been reported. In January 2000, there was an outbreak of gastroenteritis in an infant home in Sapporo, Japan. Of 34 residents of the home that were less than 2 years old, 23 developed gastrointestinal symptoms and NV infection was confirmed by conventional reverse transcription-PCR to detect the RNA polymerase region of genogroup II NV. In this virus, the RNA polymerase region shared 86% nucleotide identity with Hawaii virus but only 77% with Mexico virus; however, its capsid region shared only 70% identity with Hawaii virus but 90% with Mexico virus. On the other hand, both regions shared a higher 96% nucleotide identity with Arg320 virus, which was found in Mendoza, Argentina, in 1995 and considered to be a recombinant of Hawaii and Mexico viruses. The findings indicate that the virus involved in the outbreak was similar and may have evolved from the Arg320 virus. Clinically the cases were more severe than those of previously reported sporadic or outbreak cases of NV infection.

FIG. 1.

Phylogenetic trees of the amino acid sequences of the RNA polymerase (A), capsid (B) and ORF3 (C) regions of SN2000JA, Arg320, Hawaii, Mexico, Lordsdale, Melksham, Norwalk, Sh-5, Ueno7k, and Chiba viruses. Only the capsid regions of Sh-5 and Ueno7k viruses were included. Trees were drawn using TreeView program version 1.6.6. Partial amino acid sequences of the RNA polymerase (from N36 primer to the end of the gene) and the entire capsid and ORF3 gene were aligned and 1,000 boot-strapped samples were analyzed using Clustal W. The bars indicate the number of substitutions per site. For each node, bootstrap values are indicated.

FIG. 1.

Phylogenetic trees of the amino acid sequences of the RNA polymerase (A), capsid (B) and ORF3 (C) regions of SN2000JA, Arg320, Hawaii, Mexico, Lordsdale, Melksham, Norwalk, Sh-5, Ueno7k, and Chiba viruses. Only the capsid regions of Sh-5 and Ueno7k viruses were included. Trees were drawn using TreeView program version 1.6.6. Partial amino acid sequences of the RNA polymerase (from N36 primer to the end of the gene) and the entire capsid and ORF3 gene were aligned and 1,000 boot-strapped samples were analyzed using Clustal W. The bars indicate the number of substitutions per site. For each node, bootstrap values are indicated.

FIG. 1.

Phylogenetic trees of the amino acid sequences of the RNA polymerase (A), capsid (B) and ORF3 (C) regions of SN2000JA, Arg320, Hawaii, Mexico, Lordsdale, Melksham, Norwalk, Sh-5, Ueno7k, and Chiba viruses. Only the capsid regions of Sh-5 and Ueno7k viruses were included. Trees were drawn using TreeView program version 1.6.6. Partial amino acid sequences of the RNA polymerase (from N36 primer to the end of the gene) and the entire capsid and ORF3 gene were aligned and 1,000 boot-strapped samples were analyzed using Clustal W. The bars indicate the number of substitutions per site. For each node, bootstrap values are indicated.

FIG. 2.

Nucleotide identity plotting between the query sequence (SN2000JA) and the other three strains (Arg320, Hawaii, and Mexico viruses) using SimPlot program. A window size of 160 nucleotides with an increment of 40 was used. The vertical axis indicates the nucleotide similarity between the query sequence and the other reference strains expressed as a percentage. The horizontal axis indicates nucleotide positions.