Abstract
Human noroviruses in the family Caliciviridae are a major cause of epidemic gastroenteritis. They are responsible for at least 95% of viral outbreaks and over 50% of all outbreaks worldwide. Transmission of these highly infectious plus-stranded RNA viruses occurs primarily through contaminated food or water, but also through person-to-person contact and exposure to fomites. Norovirus infections are typically acute and self-limited. However, disease can be much more severe and prolonged in infants, elderly, and immunocompromised individuals. Norovirus outbreaks frequently occur in semi-closed communities such as nursing homes, military settings, schools, hospitals, cruise ships, and disaster relief situations. Noroviruses are classified as Category B biodefense agents because they are highly contagious, extremely stable in the environment, resistant to common disinfectants, and associated with debilitating illness. The number of reported norovirus outbreaks has risen sharply since 2002 suggesting the emergence of more infectious strains. There has also been increased recognition that noroviruses are important causes of childhood hospitalization. Moreover, noroviruses have recently been associated with multiple clinical outcomes other than gastroenteritis. It is unclear whether these new observations are due to improved norovirus diagnostics or to the emergence of more virulent norovirus strains. Regardless, it is clear that human noroviruses cause considerable morbidity worldwide, have significant economic impact, and are clinically important emerging pathogens. Despite the impact of human norovirus-induced disease and the potential for emergence of highly virulent strains, the pathogenic features of infection are not well understood due to the lack of a cell culture system and previous lack of animal models. This review summarizes the current understanding of norovirus pathogenesis from the histological to the molecular level, including contributions from new model systems.
Highlights
Noroviruses constitute a genus within the family Caliciviridae
Based on a recent review of diagnostic studies testing for norovirus infections in clinical settings, it is estimated that they cause over one million hospitalizations and 200,000 deaths in young children in developing countries annually [2]
In one human volunteer study, it was observed that norovirus infection causes a marked delay in gastric emptying thought to be related to the high incidence of vomiting episodes during norovirus infections [82]
Summary
Noroviruses constitute a genus within the family Caliciviridae. The human pathogens within this genus cause at least 95% of nonbacterial gastroenteritis outbreaks, and 50% of all gastroenteritis outbreaks, throughout the world. Noroviruses are highly transmissible and can spread via exposure to contaminated food or water sources, person-to-person contact, aerosolized vomitus particles, and fomites (Figure 1A). They are considered by CDC to be the most common cause of foodborne disease outbreaks [3]. There has been a dramatic increase in the number of reported norovirus outbreaks. These emerging RNA viruses have historically been very difficult to study but numerous advances in the field have begun to contribute to the overall understanding of norovirus pathogenesis
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