Rotaviruses are the leading cause of severe, dehydrating diarrhoea in children aged less than 5 years globally, with an estimated more than 25 million outpatient visits and more than 2 million hospitalizations attributable to rotavirus infections each year. In developing countries, three-quarters of children acquire their first episode of rotavirus diarrhoea before the age of 12 months, whereas in developing countries the first episode is frequently delayed until the age of 2-5 years. Severe rotavirus gastroenteritis is largely limited to children aged 6-24 months.
Rotaviruses are shed in very high concentrations and for many days in the stools and vomitus of infected individuals. Transmission occurs primarily by the faecal-oral route, directly from person to person or indirectly via contaminated fomites. The universal occurrence of rotavirus infections shows that clean water supplies and good hygiene are unlikely to have a substantial effect on virus transmission.
Rotaviruses are classified as a genus in the family of Reoviridae. The triple-layered viral particle encompasses a viral genome consisting of 11 genome segments of double-stranded RNA that encode 6 structural viral proteins (VPs) and 6 non-structural viral proteins (NSPs). Reassortment of the 11 gene segments may take place in coinfected host cells during the viral replication cycle. Formation of reassortants is in part responsible for the wide variety of rotavirus strains found in nature; even reassortants of animal-human strains have been identified.
The outermost viral layer contains the structural viral proteins VP7 and VP4, which elicit the production of neutralizing antibodies in the host and are considered important for protective immunity. In humans, at least 11 different VP7 antigens (G-types) and 11 different VP4 antigen (P-types) have been identified. As the combination of G- and P-types can vary independently, a binomial typing system is used to identify strains.