Fecal viral load and norovirus-associated gastroenteritis

Abstract

We report the median cDNA viral load of norovirus genogroup II is >100-fold higher than that of genogroup I in the fecal specimens of patients with norovirus-associated gastroenteritis. We speculate that increased cDNA viral load accounts for the higher transmissibility of genogroup II strains through the fecal-oral route.

Figure 1

Scatterplots for cDNA viral load of noroviruses (NoV) genogroup I (GI) and GII. A) All positive isolates. B) All positive isolates, excluding those with NoV GI/GII coinfection. C) All positive isolates, excluding all those with viral coinfection (NoV GI and GII together with sapovirus, group A rotavirus, or both). The bars represent median cDNA viral loads. The p values were calculated by 2-tailed Mann-Whitney U test.

Figure 2

cDNA viral load in 9 specimens with norovirus (NoV) genogroup I (GI) and GII coinfection.

Figure A1

Monthly distribution of cDNA viral load of norovirus (NoV) genogroup I (GI) and GII during the study period (December 2004 through November 2005). In the scatterplot, cDNA viral loads of NoV GI and GII are represented by open and solid squares, respectively. Lowess fit lines for the seasonal variation of the cDNA viral loads of NoV GI and GII are represented by dashed and solid lines, respectively. Local monthly mean air temperature (temp.) is tabulated.

Figure A2

Phylogenetic analysis of norovirus genogroup I nucleotide sequences. The phylogenetic tree was generated by neighbor-joining analysis of the partial nucleotide sequences of the capsid N-terminal/Shell domain with bootstrapping of 1,000 replicates using MEGA version 3.1. Isolates identified in this study are highlighted in boldface. Bootstrap values >80 are shown at each node as percentage of 1,000 replicates. The scale bar represents the estimated number of substitutions per site. Nucleotide sequences obtained in this study were deposited in GenBank under accession nos. DQ522116–DQ522122. Nucleotide sequences of reference strains: DSV-USA93 (GenBank accession no. U04469, genotype GI/3), Musgrov-GBR00 (AJ277614, GI/5), Hesse-DEU98 (AF093797, GI/6), Wnchest-GBR00 (AJ277609, GI/7), and Boxer-USA02 (AF538679, GI/8).

Figure A3

Phylogenetic analysis of norovirus genogroup II nucleotide sequences. The phylogenetic tree was generated by neighbor-joining analysis of the partial nucleotide sequences of the capsid N/S domain with bootstrapping of 1,000 replicates using MEGA version 3.1. Isolates identified in this study are highlighted in boldface. Bootstrap values >80 are shown at each node as percentage of 1,000 replicates. The scale bar represents the estimated number of substitutions per site. Nucleotide sequences obtained in this study were deposited in GenBank under accession nos. DQ522123–DQ522158. Nucleotide sequences of reference strains: Msham-GBR95 (GenBank accession no. X81879, genotype GII/2), Toronto-CAN93 (U02030, GII/3), Bristol-GBR93 (X76716, GII/4), Hilingd-GBR00 (AJ277607, GII/5), Seacrof-GBR00 (AJ277620, GII/6), Faytvil-USA02 (AY113106, GII/13), M7-USA03 (AY130761, GII/14), and Tiffin-USA03 (AY502010, GII/16).