1 INTRODUCTION
Rotavirus A (RVA) is considered as the leading cause of acute gastroenteritis (AGE) in infants and young children under 5 years of age worldwide. RVA infection is associated with significant morbidity and mortality, which is responsible for an estimated 251,000 deaths per year. More than 90% of RVA-related deaths and hospitalizations occur in low-income countries, particularly in sub-Saharan Africa and South Asia.1
RVA is a member of the Reoviridae family. The infectious RVA virion is a triple-layered, nonenveloped icosahedron containing 11 dsRNA segments encoding six structural proteins (VP1-VP4, VP6, VP7) and six nonstructural proteins (NSP1-NSP5/6). The outer capsid proteins, VP7 and VP4, carry the major antigenic determinants that independently elicit neutralizing antibodies. Based on nucleotide sequence variations of the VP7 and VP4 genes, RVA strains are classified into G- and P-genotypes, respectively. To date, at least 42 G- and 58 P-genotypes are known. G1P[8], G2P[4], G3P[8], G4P[8], G9P[8], and G12P[8] represent the most common and widespread strains causing gastroenteritis in humans.2-6
The whole genome-based genotyping nomenclature has been developed to assign the genotype constellation of RVA. This system incorporates Gx-P[x]-Ix-Rx-Cx-Mx-Ax-Nx-Tx-Ex-Hx, where ”x” is an integer defining the corresponding genotypes of the VP7-VP4-VP6-VP1-VP2-VP3-NSP1-NSP2-NSP3-NSP4-NSP5 genes. There are three genogroup constellations of human RVA strains: genogroup I with the Wa-like constellation (G1/3/4/9-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1), genogroup II with the DS-1-like constellation (G2-P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2), and genogroup III with the AU-like constellation (G3-P[9]-I3-R3-C3-M3-A3-N3-T3-E3-H3). RVA strains of genogroup I, II, and III have been reported to carry the gene segments of pigs, cattle, and cats/rabbits, respectively.7 Currently, several genotypes of each gene have been identified for human and animal rotaviruses: 42 G, 58 P, 32 I, 28 R, 24 C, 24 M, 39 A, 28 N, 28 T, 32 E, and 28 H (https://rega.kuleuven.be/cev/ viralmetagenomics/virus-classification/rcwg).
There are two live-attenuated rotavirus vaccines (Rotarix and RotaTeq) licensed in many countries, including Thailand. Rotarix (RV1) is a monovalent vaccine made from a single human G1P[8] strain, while RotaTeq (RV5) is a pentavalent vaccine consisting of a mixture of five reassortant bovine RVA strains: G1P[5], G2P[5], G3P[5], G4P[5], and G6P[8]. The RVA vaccines have been shown to be safe and highly effective in preventing acute gastroenteritis against a broad spectrum of RVA strains and have significantly reduced deaths and hospitalizations.8 The impact of vaccine use has inevitably reflected in changes in local and global distribution patterns of RVA genotypes.9-11
RVA G8P[8] strains, which are commonly found in cattle, have been frequently detected in humans in the post-vaccination period in many countries, including Argentina, Chile, China, the Czech Republic, Japan, Korea, Singapore, Thailand, and Vietnam.12-27Surveillance of RVA in Chiang Rai province of Thailand has continuously monitored the diversity and distribution of RVA since 2015 and reported the emergence of G9P[8] in 2015-2016 and the equine-like G3P[8] in 2016-2018.3,4 The purpose of the present study was to investigate the molecular epidemiology and characterization of RVA strains in children hospitalized with acute gastroenteritis in Chiang Rai, Thailand from 2018 to 2020.