Abstract
Noroviruses are endemic in the human population, and are recognised as a leading cause of acute gastroenteritis worldwide. Although they are a highly diverse group of viruses, genogroup-II genotype-4 (GII-4) noroviruses are the most frequently identified strains worldwide. The predominance of GII-4 norovirus strains is driven by the periodic emergence of antigenic variants capable of evading herd protection. The global molecular epidemiology of emerging GII-4 strains is largely based on data from outbreak surveillance programmes, but the epidemiology of GII-4 strains among sporadic or community cases is far less well studied. To understand the distribution of GII-4 norovirus strains associated with gastroenteritis in the wider population, we characterised the GII-4 norovirus strains detected during studies of sporadic cases of infectious gastroenteritis collected in the UK and Malawi between 1993 and 2009. Our data shows that GII-4 norovirus strains that have emerged as strains of global epidemic importance have circulated in the community up to 18 years before their recognition as pandemic strains associated with increases in outbreaks. These data may suggest that more comprehensive surveillance programmes that incorporate strains associated with sporadic cases may provide a way for early detection of emerging strains with pandemic potential. This may be of particular relevance as vaccines become available.
Highlights
Noroviruses are endemic throughout the human population, and are recognised as the leading cause of acute gastroenteritis worldwide [1, 2]
The Infectious Intestinal Disease (IID) study I samples were obtained from cases of gastroenteritis of all ages in the community or attending general practice and healthy controls in the community [26], whilst IID2 samples were from cases only, in the community or attending general practice, in the UK [10, 29]
Molecular Epidemiology of GII-4 Strains Detected in UK and Malawi
Summary
Noroviruses are endemic throughout the human population, and are recognised as the leading cause of acute gastroenteritis worldwide [1, 2]. In the UK, there are an estimated three million cases of norovirus gastroenteritis in the community each year [10], and in elderly and immunosuppressed individuals, norovirus gastroenteritis can contribute to excess deaths [11]. Genetic diversity in the major capsid protein (VP1) is used to classify noroviruses into five genogroups (GI-GV). The majority of strains associated with disease in humans belong to GI and GII, which are further subdivided into multiple genotypes [14, 15]. The most frequently detected norovirus genotype worldwide is genogroup-II genotype-4 (GII-4)
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