Norovirus Gastroenteritis Outbreaks, Genomic Diversity and Evolution: An Overview.

Norovirus, often called winter vomiting bug, is the most common cause of outbreaks of acute gastroenteritis in all age groups all over the world. It was discovered in 1972; belong to the genus Norovirus in the family Caliciviridae. Based on genomic organization and phylogenetic analysis, the family Caliciviridae is divided into four genera- Norovirus, Sapovirus, Vesivirus and Lagovirus. The aim of this review article was to find out the present status of prevalence and evolution of norovirus strains in developed and developing countries. In this article various literature on norovirus from different countries was reviewed. The detection of norovirus in the lower middle income countries (LMIC) was reported 15% in cases and 8% in controls during 1997 to 2018. On the other hand, detection rate of norovirus in low income countries (LIC) was 11% in cases and 9% in controls during the same period. Overall detection rate of norovirus was 14% in LIMC and 8% in LIC during 1997 to 2018. Noroviruses are divided genetically into seven different type of Geno groups namely GI, GII, GIII, GIV, GV, GVI and GVII which are further classified into different genetic clusters or genotypes. For example, Geno group II, the most prevalent human Geno group, presently contains 19 genotypes. Among the genogroups I, II and IV infect humans, on the other hand genogroup III infects bovine species and genogroup V was isolated from mice. Several new noroviruses were reported and the number of genogroups increased to 10 (GI-GX) and the number of genotypes expanded to 49: 9 GI, 27 GII, 3 GIII, 2 GIV, 2 GV, 2GVI, 1 GVII, 1 GVIII, 1 GIX, 1 GX. Noroviruses are spread directly from individual to individual as well as indirectly via contaminated food and water. They are highly contagious, and around twenty virus particles can cause an infection. This virus usually exhibits winter seasonality. The global norovirus prevalence in under-5 years, ≥5 years and mixed age was similar (16% - 19%). Norovirus infection is characterized by diarrhea, vomiting, fever, headache and stomach pain. It may be complicated with dehydration and electrolyte imbalance. Gastroenteritis develops 12 to 48 hours after exposure and recovery typically occurs within 1 to 3 days. There is no specific treatment of norovirus gastroenteritis. Prevention includes proper hand washing and cleaning or disinfection of contaminated surfaces. Various genotypes of norovirus may be circulating around the world and can emerge either nationally or globally. In this overview, general characteristics of norovirus, current status of genomic diversity and classification, recent status of norovirus gastroenteritis outbreaks in the developed and developing countries is outlined for comprehensive understanding of the present status of prevalence and evolution of norovirus strains to develop strategies for prevention and control of norovirus infection in human.