Rotavirus

Rotaviruses are the most common cause of severe diarrhoeal disease in infants and young children worldwide; in 2004, rotavirus infections were estimated to cause approximately 527 000 (475 000-580 000) deaths, predominantly in developing countries. Although the viral strains show considerable diversity, 5 serotypes are responsible for the majority of human rotavirus disease. Primarily transmitted by the faecal-oral route, rotaviruses affect the vast majority of children worldwide before the age of 3 years, and in most developing countries before the first birthday.

Two new live, oral, attenuated rotavirus vaccines were licensed in 2006. Both vaccines have demonstrated very good safety and efficacy profiles in large clinical trials in western industralized countries and in Latin America. Careful surveillance has not revealed any increased risk of intussusception in the vaccinated groups with either vaccines. The new rotavirus vaccines are now introduced for routine use in a number of industrialized and developing countries.

Background

Epidemiology

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.


The pathogen

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.