Norovirus: An Overview of Virology and Preventative Measures

Abstract

Norovirus (NoV) is an enteric non-enveloped virus which is the leading cause of gastroenteritis across all age groups. It is responsible for around 200,000 deaths annually and outbreaks are common in small communities such as educational and care facilities. 40% of all NoV outbreaks occur in long-term and acute-care facilities, forming the majority of outbreaks. Nosocomial settings set ideal environments for ease of transmission, especially due to the presence of immunocompromised groups. It is estimated to cost global economies around £48 billion a year, making it a global issue. NoV is transmitted via the faecal-oral route and infection with it results in asymptomatic cases or gastrointestinal disease. It has high mutational rates and this allows for new variants to emerge and be more resistant. The classification system available divides NoV into 10 genogroups and 49 genotypes based on whole amino acid sequencing of VP1 capsid protein and partial sequencing of RdRp, respectively. The most predominant genotypes which cause gastroenteritis in humans include GI.1 and GII.4, where GII.4 is responsible for more extreme clinical implications such as hospitalisation. In addition, GII.4 has been responsible for 6 pandemic strains, the last of which is the GII.4 Sydney (2012) variant. In recent years, the successful cultivation of HuNoV was reported in stem cell-derived human intestinal enteroids (HIEs), which promises to assist in giving a deeper understanding of its underlying mechanisms of infection and the development of more personalized control measures. There are no specific control measures against NoV, therefore common practices are used against it such as hand washing. No vaccine is available, but the HIL-214 candidate passed clinical phase 2b and shows promise.

Genetic characterizations and molecular evolution of human norovirus GII.6 genotype during the past five decades

“…Variant replacement is an important pattern of norovirus to adapt to different immunological environments. 9 Ladder-like phylogenetic relationship of strains indicates a temporal replacement of prevalent variants driven by herd immunity. 40 But this was not observed in the GII.6 VP1 gene, indicating the long-term cocirculation of GII.6 variants in the population.…”

“…MCC tree also confirmed that GII.6 VP1 gene was clustered into three groups. Variant replacement is an important pattern of norovirus to adapt to different immunological environments 9 . Ladder‐like phylogenetic relationship of strains indicates a temporal replacement of prevalent variants driven by herd immunity 40 .…”

“…Norovirus GII is the most prevalent norovirus genogroup in the whole world 9 . GII.4 variants have caused at least six pandemics of AGE, 10 and a novel recombinant variant of GII.P16‐GII.4 Sydney 2012 was detected in 2014 11 .…”

Asymptomatic norovirus infection during outbreaks in China: A systematic review and meta‐analysis

“…2 It causes around 685 million cases worldwide each year, of which around 200 million are children under the age of 5, around 200 000 deaths (mainly in underdeveloped countries), and costs worldwide economic losses of around £48 billion per year, making it a global problem. 3,4 For this reason, the development of a vaccine against NoV is now considered a high priority by the World Health Organization. 5 Currently, the NoV GI and GII variants are the most commonly detected genogroups worldwide.…”

“…Norovirus (NoV) is the main pathogen causing AGE sporadic cases and outbreaks worldwide, causing at least 50% of gastroenteritis outbreaks and a major cause of foodborne illness 2 . It causes around 685 million cases worldwide each year, of which around 200 million are children under the age of 5, around 200 000 deaths (mainly in underdeveloped countries), and costs worldwide economic losses of around £48 billion per year, making it a global problem 3,4 . For this reason, the development of a vaccine against NoV is now considered a high priority by the World Health Organization 5 .…”