Predicting Directions of Changes in Genotype Proportions Between Norovirus Seasons in Japan.

Yoshiyuki Suzuki,Kazuhiko Katayama,Komei Shirabe,Hirokazu Kimura,Yen Hai Doan,Hiroto Shinomiya

doi:10.3389/fmicb.2019.00116

Abstract

The norovirus forecasting system (NOROCAST) has been developed for predicting directions of changes in genotype proportions between human norovirus (HuNoV) seasons in Japan through modeling herd immunity to structural protein 1 (VP1). Here 404 nearly complete genomic sequences of HuNoV were analyzed to examine whether the performance of NOROCAST could be improved by modeling herd immunity to VP2 and non-structural proteins (NS) in addition to VP1. It was found that the applicability of NOROCAST may be extended by compensating for unavailable sequence data and observed genotype proportions of 0 in each season. Incorporation of herd immunity to VP2 and NS did not appear to improve the performance of NOROCAST, suggesting that VP1 may be a suitable target of vaccines.

Highlights

Norovirus (NoV) is an etiological agent of acute gastroenteritis in humans (Kapikian et al, 1972), causing 18% of all cases (Ahmed et al, 2014) and 200,000 deaths worldwide annually (Patel et al, 2008)
When only the herd immunity to VP1 was taken into account without replacing the observed genotype proportions of 0, the numbers of correct and incorrect predictions were 66 and 62, respectively, yielding the accuracy of 0.516 (P = 0.724 by the χ2 test) (Table 1)
In the previous study (Suzuki et al, 2016), NOROCAST was developed for predicting directions of changes in genotype proportions between human norovirus (HuNoV) seasons in Japan modeling the herd immunity to VP1

Summary

Introduction

Norovirus (NoV) is an etiological agent of acute gastroenteritis in humans (Kapikian et al, 1972), causing 18% of all cases (Ahmed et al, 2014) and 200,000 deaths worldwide annually (Patel et al, 2008). The human NoV (HuNoV) is more prevalent in developed countries (20%) and low-mortality developing countries (19%) than in high-mortality developing countries (14%) (Ahmed et al, 2014). The virion of HuNoV is non-enveloped, icosahedral, and 38 nm in diameter (Prasad et al, 1999). The genome of HuNoV is a linear, non-segmented, single-stranded, positive-sense RNA of 7.5 kb, containing ORF1-ORF3 (Jiang et al, 1993; Lambden et al, 1993). ORF1 encodes non-structural proteins (NS), whereas ORF2 and ORF3 encode structural proteins 1 (VP1) and 2 (VP2), respectively

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