Chapter 43 - Emergence of Norovirus Strains in Worldwide Distribution and Environmental Spreading

Abstract

Norovirus (NoV) is considered to be the common cause of gastroenteritis in humans all over the world, and it is also a crucial cause of sporadic gastroenteritis in both children and adults. Based on evidences, it is demonstrated that the continuous emergence of genogroup II of NoV is related primarily to the fecal–oral transmission. The spread of NoV is caused by several characteristics, such as their low infectious dose (approximately 18–1000 viral particles) which allows its spread through droplets, fomites, person-to-person contact, consumption of contaminated water or food, and environmental contamination. Accordingly, the emergence of NoV strains occurs either at the global or the national level, and it can also displace other strains causing an increase in disease incidence. NoV GII is deemed as the most common emerging genotype in human infection. Air travels is one of the factors that promotes the spread of NoV GII worldwide. It was first reported in Africa and South America and recently was identified as an outbreak strain in Japan and China. The existence of this genotype is present all over the world but there are some strains that their presence differs from one geographic zone to another. Also, several studies have detected human NoV in imported food matrixes, which reveal that they are an important vehicle of infection. For instance, in 2002, the emergence of a new virus variant on cruise ships and in nursing homes in the United States has caused the outbreak of NoV in Europe. What was noticeable in the previous studies that the understanding of the emergence of genogroup II was not clear enough; later predominance of GII.4 has been explained. In this chapter, we are going to highlight and discuss the role of NoV emergence by environment, food, and water matrix.