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Chapter 3 : Norovirus Gastroenteritis
Category: Clinical Microbiology
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Outbreak and volunteer studies provided significant information on host genetic factors that control susceptibility to norovirus infection. The recent elucidation of the type-specific recognition of histo-blood group antigens (HBGAs) as receptors for noroviruses helped to explain a controversy between clinical illness and immunity of norovirus gastroenteritis that had puzzled the field for many years. Noroviruses are transmitted by the fecal-oral pathway through person-to-person contact, contaminated environmental surfaces, and contaminated water or food, frequently causing large outbreaks. The widespread nature and multiple transmission modes of norovirus gastroenteritis can be explained by the low infectious dose and the high environmental stability of noroviruses and the lack of long-term host immunity. Due to the lack of cell culture methods or an animal model, the minimum infectious dose leading to norovirus gastroenteritis has not yet been thoroughly determined. Norovirus gastroenteritis is relatively mild, lasts for 12 to 48 h, and usually self-resolves. The increasing number of animal noroviruses that are genetically closely related to human isolates has also raised the issues of interspecies transmission of norovirus gastroenteritis and whether animal species can serve as reservoirs for human infections, although direct evidence for this remains lacking. The overall host specificity of noroviruses may not change in the course of long-term infection, but subtle modifications of the capsid surface, particularly the receptor binding interface, may occur, resulting in clones with better fitness. Recent new findings on host-pathogen interactions, molecular evolution, and host immune responses of noroviruses provide valuable information for developing future prevention and intervention strategies.