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.