Rotavirus can cause severe diarrhea. Human group A rotaviruses are the most frequently identified etiologic agents in children hospitalized due to acute, severe, dehydrating diarrhea worldwide. Rotavirus infections range in presentation from asymptomatic mild infections to severe and sometimes fatal disease. An estimated 450,000 children who are less than 5 years old die of rotavirus infections each year, most in developing countries. The rotaviruses are in term of combinations of G and P type, refer to serotype designation and genotypic designation. For example, G1P1A is the combination of P1A serotype and G genotypic designation, while the G2P1B, G3P1A and G4P1A are the most frequent phenotype in human infections. However, other G types are predominant in various geographical settings: G5 (found in pigs and horses) in Brazil, G8 (found in cattle) in various parts of Africa, and G10 (found in cattle) in India. Since 1995, the G9 strain (found in pigs) has infected humans in most continents, suggesting a possible emergence of a fifth com- mon G type worldwide.
Rotaviruses are triple-layered icosahedral particles, and their genomes consist of 11 segments of double-stranded RNA. Rotaviruses are classified according to the genetic and antigenic diversity of the two outer capsid proteins, VP4 and VP7. These proteins independently induce type-specific neutralizing antibodies and form the basis of the present dual classification of group A rotaviruses into P (protease sensitive) and G (glycoprotein) subtypes, respectively. Rotaviruses express an extensive antigenic and genomic diversity. To date, 14 G serotypes and 20 P types have been defined, but a 15th G serotype and a 21st P genotype based on nucleotide sequence characterizations of a bovine rotavirus strain have been proposed. Reassortment of genes can occur upon dual infection of a single cell with two different strains in vivo as well as in vitro. As the segregations of VP4 genes and VP7 genes occur independently, various G and P combinations have been observed in natural infections. Figure 1 shows the schematic model of the rotavirus:
Fig. 1 The Schematic Model of the Rotavirus