Prevalence and molecular characterization of G1P[8] human rotaviruses possessing DS-1-like VP6, NSP4, and NSP5/6 in Japan

Emergence and dissemination of equine-like G3P[8] rotavirus A in Brazil between 2015 and 2021

Rotavirus A (RVA) is a major cause of acute gastroenteritis globally that is classically genotyped by its two immunodominant outer capsid proteins, VP7 (G-) and VP4 (P-). Recent evidence suggests that the reassortant equine-like G3P[8] strain played a substantial role in RVA transmission in Brazil since 2015. To understand its global emergence and dissemination in Brazilian territory, stool samples collected from 11 Brazilian states (n = 919) were genotyped by RT-qPCR and proceeded to sequence the VP7 gene (n = 102, 79 being newly generated) of the G3P[8] samples with pronounced viral loads. Our phylogenetic genotyping showed that G3P[8] became the dominant strain in Brazil between 2017 and 2020, with equine-like variants representing 75%-100% of VP7 samples in this period. A Bayesian discrete phylogeographic analysis strongly suggests that the equine-like G3P[8] strain originated in Asia during the early 2010s and subsequently spread to Europe, the Caribbean, and South America. Multiple introductions were detected in Brazil between 2014 and 2017, resulting in five national clusters. The reconstruction of the effective population size of the largest Brazilian cluster showed an expansion until 2017, followed by a plateau phase until 2019 and subsequent contraction. Our study also supports that most mutations fixed during equine-like G3P[8] evolution were synonymous, suggesting that adaptive evolution was not an important driving force during viral dissemination in humans, potentially increasing its susceptibility to acquired immunity. This research emphasizes the need for comprehensive rotavirus genomic surveillance that allows close monitoring of its ever-shifting composition and informs more effective public health policies.IMPORTANCEOur original article demonstrated the origin and spread in a short time of equine-like G3P[8] in Brazil and the world. Due to its segmented genome, it allows numerous mechanisms including genetic drift and reassortment contribute substantially to the genetic diversity of rotavirus. Although the effectiveness and increasing implementation of vaccination have not been questioned, a matter of concern is its impact on the emergence of escape mutants or even the spread of unusual strains of zoonotic transmission that could drive epidemic patterns worldwide. This research emphasizes the need for comprehensive rotavirus genomic surveillance, which could facilitate the formulation of public policies aimed at preventing and mitigating its transmission.

Full genotype constellations analysis of unusual DS-1-like G12P[6] and G6P[8] rotavirus strains detected in Brazil, 2019

Rotavirus A (RVA) is a major cause of acute gastroenteritis (AGE) in children worldwide. We report unusual RVA G12P[6] and G6P[8] strains isolated from fecal samples from Brazilian children hospitalized for AGE. The characterized RVA have genome segments backbone: G12-P[6]/ G6-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 of DS-1-like genogroup. Our study describes the first identification of G6P[8], a DS-1-like genogroup strain. Nucleotide analysis of VP7 and VP4 genes revealed that all G12 Brazilian strains clustered into the sub-lineages IIIB, mostly associated with P[6] lineage I. Additionally, our G6 lineage I strains were closely related to German G6 genotypes, bound with P[8] lineage III, differing from both vaccine strains. The comparative sequence analysis of our strains with vaccine strains revealed amino acid substitutions located in immunodominant regions of VP7 and VP4 proteins. Continuous monitoring of RVA genotypes is essential to evaluate the impact of vaccination on the dynamic nature of RVA evolution.

Changing distribution of rotavirus A genotypes circulating in Japanese children with acute gastroenteritis in outpatient clinic, 2014-2020

BACKGROUND

Rotavirus A (RVA) is a major cause of severe acute gastroenteritis (AGE) in infants and children worldwide. In Japan, two kinds of rotavirus vaccines have been introduced as voluntary vaccines in 2011 and 2012, respectively, and launched into the national vaccine program in October 2020.

METHODS

In this study, we investigated prevalence of RVA and their molecular characterization in the stool samples collected from infants and children with AGE who visited one outpatient clinic in Japan, from July 2014 to June 2020, during voluntary vaccination with two kinds of rotavirus vaccines.

RESULTS

The RVA detection rates decreased from 44.7 % in 2014-2015 to 35.4 % in 2018-2019, whereas in 2019-2020 the numbers of samples collected were dramatically decreased and none of RVA was detected. During this study period, rotavirus vaccination rates in this area increased from 32.4 % to 62.2 %. Distribution of RVA VP7 (G), VP4 (P), and VP6 (I) genotypes in this area had changed year by year; the major genotype combinations were G1P[8]I1 and G1P[8]I2 in 2014-2015, G2P[4]I2 and G9P[8]I1 in 2015-2016, G1P[8]I1 and G8P[8]I2 in 2017-2018, and G8P[8]I2 in 2018-2019. Phylogenetic analysis demonstrated that VP7 nucleotide sequences of G1 were genetically diverse compared with those of other G genotypes in this study. Meanwhile, predominance of unusual G2P[8]I1, G2P[8]I2 and mixed P genotypes were observed only in 2016-2017, but did not carry on in 2017-2019. The equine-like G3 was detected only in 2016-2017.

CONCLUSIONS

The results revealed diversity of RVA genotypes and the genotype combinations have changed year by year in Japan, during the study period of 2016-2020.

Rotavirus vaccination in Japan: Efficacy and safety of vaccines, changes in genotype, and surveillance efforts

In Japan, a monovalent rotavirus vaccine (RV1) and a pentavalent rotavirus vaccine (RV5) were launched as voluntary vaccinations in November 2011 and July 2012, respectively. Rotavirus (RV) vaccine coverage in Japan increased from 30.0% in 2012 to 78.4% in 2019. The number of RV gastroenteritis hospitalizations decreased after 2014 in Japan, and is expected to decrease further following the introduction of RV vaccines into the national immunization program in October 2020. The incidence rates of intussusception (IS) among children aged <1 year were 102.8 and 94.0 per 100,000 person-years in the pre-vaccine (2007-2011) and post-vaccine (2012-September 2014) eras, respectively. IS incidence did not increase following RV vaccine introduction in Japan. The efficacy and safety of RV vaccination were both documented in Japan. To reduce the risk of IS following RV vaccination, it is important that children receive a first dose of RV vaccine at age <15 weeks, preferably at age 2 months. Some strains that have emerged since RV vaccine introduction, such as DS-1-like G1P[8], eG3, and G8P[8], have spread nationwide. These three emerging genotypes did not affect the severity of the RV infection. Continuous city-level surveillance, using analysis of all 11 RV genome segments, is necessary to elucidate the genetic characteristics of prevalent RV strains. These efforts would also clarify the influence of vaccination on genetic changes of RV strains and the emergence of new genotypes.

High prevalence of circulating DS-1-like human rotavirus A and genotype diversity in children with acute gastroenteritis in Thailand from 2016 to 2019

Background

Human rotavirus A (RVA) infection is the primary cause of acute gastroenteritis (AGE) in infants and young children worldwide, especially in children under 5 years of age and is a major public health problem causing severe diarrhea in children in Thailand. This study aimed to investigate the prevalence, genotype diversity, and molecular characterization of rotavirus infection circulating in children under 15 years of age diagnosed with AGE in Thailand from January 2016 to December 2019.

Methods

A total of 2,001 stool samples were collected from children with gastroenteritis (neonates to children <15 years of age) and tested for RVA by real-time polymerase chain reaction (RT-PCR). Amplified products were sequenced and submitted to an online genotyping tool for analysis.

Results

Overall, 301 (15.0%) stool samples were positive for RVA. RVA occurred most frequently among children aged 0-24 months. The seasonal incidence of rotavirus infection occurred typically in Thailand during the winter months (December-March). The G3P[8] genotype was identified as the most prevalent genotype (33.2%, 100/301), followed by G8P[8] (10.6%, 32/301), G9P[8] (6.3%, 19/301), G2P[4] (6.0%, 18/301), and G1P[6] (5.3%, 16/301). Uncommon G and P combinations such as G9P[4], G2P[8], G3P[4] and G3P[9] were also detected at low frequencies. In terms of genetic backbone, the unusual DS-1-like G3P[8] was the most frequently detected (28.2%, 85/301), and the phylogenetic analysis demonstrated high nucleotide identity with unusual DS-1-like G3P[8] detected in Thailand and several countries.

Conclusions

A genetic association between RVA isolates from Thailand and other countries ought to be investigated given the local and global dissemination of rotavirus as it is crucial for controlling viral gastroenteritis, and implications for the national vaccination programs.

Molecular and clinical characterization of the equine-like G3 rotavirus that caused the first outbreak in Japan, 2016

Since 2013, equine-like G3 rotavirus (eG3) strains have been detected throughout the world, including in Japan, and the strains were found to be dominant in some countries. In 2016, the first eG3 outbreak in Japan occurred in Tomakomai, Hokkaido prefecture, and the strains became dominant in other Hokkaido areas the following year. There were no significant differences in the clinical characteristics of eG3 and non-eG3 rotavirus infections. The eG3 strains detected in Hokkaido across 2 years from 2016 to 2017 had DS-1-like constellations (i.e. G3-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2), and the genes were highly conserved (97.5-100 %). One strain, designated as To16-12 was selected as the representative strain for these strains, and all 11 genes of this strain (To16-12) exhibited the closest identity to one foreign eG3 strain (STM050) seen in Indonesia in 2015 and two eG3 strains (IS1090 and MI1125) in another Japanese prefecture in 2016, suggesting that this strain might be introduced into Japan from Indonesia. Sequence analyses of VP7 genes from animal and human G3 strains found worldwide did not identify any with close identity (>92 %) to eG3 strains, including equine RV Erv105. Analysis of another ten genes indicated that the eG3 strain had low similarity to G2P[4] strains, which are considered traditional DS-1-like strains, but high similarity to DS-1-like G1P[8] strains, which first appeared in Asia in 2012. These data suggest that eG3 strains were recently generated in Asia as mono-reassortant strain between DS-1-like G1P[8] strains and unspecified animal G3 strains. Our results indicate that rotavirus surveillance in the postvaccine era requires whole-genome analyses.

Whole genome and in-silico analyses of G1P[8] rotavirus strains from pre- and post-vaccination periods in Rwanda

Rwanda was the first low-income African country to introduce RotaTeq vaccine into its Expanded Programme on Immunization in May 2012. To gain insights into the overall genetic make-up and evolution of Rwandan G1P[8] strains pre- and post-vaccine introduction, rotavirus positive fecal samples collected between 2011 and 2016 from children under the age of 5 years as part of ongoing surveillance were genotyped with conventional RT-PCR based methods and whole genome sequenced using the Illumina MiSeq platform. From a pool of samples sequenced (n = 158), 36 were identified as G1P[8] strains (10 pre-vaccine and 26 post-vaccine), of which 35 exhibited a typical Wa-like genome constellation. However, one post vaccine strain, RVA/Human-wt/RWA/UFS-NGS:MRC-DPRU442/2012/G1P[8], exhibited a RotaTeq vaccine strain constellation of G1-P[8]-I2-R2-C2-M2-A3-N2-T6-E2-H3, with most of the gene segments having a close relationship with a vaccine derived reassortant strain, previously reported in USA in 2010 and Australia in 2012. The study strains segregated into two lineages, each containing a paraphyletic pre- and post-vaccine introduction sub-lineages. In addition, the study strains demonstrated close relationship amongst each other when compared with globally selected group A rotavirus (RVA) G1P[8] reference strains. For VP7 neutralization epitopes, amino acid substitutions observed at positions T91A/V, S195D and M217T in relation to the RotaTeq vaccine were radical in nature and resulted in a change in polarity from a polar to non-polar molecule, while for the VP4, amino acid differences at position D195G was radical in nature and resulted in a change in polarity from a polar to non-polar molecule. The polarity change at position T91A/V of the neutralizing antigens might play a role in generating vaccine-escape mutants, while substitutions at positions S195D and M217T may be due to natural fluctuation of the RVA. Surveillance of RVA at whole genome level will enhance further assessment of vaccine impact on circulating strains, the frequency of reassortment events under natural conditions and epidemiological fitness generated by such events.

Molecular characterization of rotaviruses obtained from patients with rotavirus-associated encephalitis/encephalopathy

Group A rotavirus (RVA) rarely causes severe complications such as encephalitis/encephalopathy. However, the pathophysiology of this specific complication remains unclear. Next-generation sequence analysis was used to compare the entire genome sequences of RVAs detected in patients with encephalitis/encephalopathy and gastroenteritis. This study enrolled eight patients with RVA encephalitis/encephalopathy and 10 with RVA gastroenteritis who were treated between February 2013 and July 2014. Viral RNAs were extracted from patients' stool, and whole-genome sequencing analysis was carried out to identify the specific gene mutations in RVA obtained from patients with severe neurological complications. Among the eight encephalitis/encephalopathy cases, six strains were DS-1-like G1P[8] and the remaining two were Wa-like G1P[8] (G1-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1). Meanwhile, eight of the 10 viruses detected in rotavirus gastroenteritis patients were DS-1-like G1P[8], and the remaining two were Wa-like G1P[8]. These strains were further characterized by conducting phylogenetic analysis. No specific clustering was demonstrated in RVAs detected from encephalitis/encephalopathy patients. Although the DS-1-like G1P[8] strain was predominant in both groups, no specific molecular characteristics were detected in RVAs from patients with severe central nervous system complications.

Uncovering the First Atypical DS-1-like G1P[8] Rotavirus Strains That Circulated during Pre-Rotavirus Vaccine Introduction Era in South Africa

Emergence of DS-1-like G1P[8] group A rotavirus (RVA) strains during post-rotavirus vaccination period has recently been reported in several countries. This study demonstrates, for the first time, rare atypical DS-1-like G1P[8] RVA strains that circulated in 2008 during pre-vaccine era in South Africa. Rotavirus positive samples were subjected to whole-genome sequencing. Two G1P[8] strains (RVA/Human-wt/ZAF/UFS-NGS-MRC-DPRU1971/2008/G1P[8] and RVA/Human-wt/ZAF/UFS-NGS-MRC-DPRU1973/2008/G1P[8]) possessed a DS-1-like genome constellation background (I2-R2-C2-M2-A2-N2-T2-E2-H2). The outer VP4 and VP7 capsid genes of the two South African G1P[8] strains had the highest nucleotide (amino acid) nt (aa) identities of 99.6–99.9% (99.1–100%) with the VP4 and the VP7 genes of a locally circulating South African strain, RVA/Human-wt/ZAF/MRC-DPRU1039/2008/G1P[8]. All the internal backbone genes (VP1–VP3, VP6, and NSP1-NSP5) had the highest nt (aa) identities with cognate internal genes of another locally circulating South African strain, RVA/Human-wt/ZAF/MRC-DPRU2344/2008/G2P[6]. The two study strains emerged through reassortment mechanism involving locally circulating South African strains, as they were distinctly unrelated to other reported atypical G1P[8] strains. The identification of these G1P[8] double-gene reassortants during the pre-vaccination period strongly supports natural RVA evolutionary mechanisms of the RVA genome. There is a need to maintain long-term whole-genome surveillance to monitor such atypical strains.

Rotavirus genotype and Vesikari score of outpatients in Japan in the vaccine era

BACKGROUND

Group A rotaviruses (RVs) are a major cause of severe gastroenteritis among infants and young children. In Japan, RV vaccines were introduced in 2011, leading to a reduction in severe gastroenteritis cases. Studies are required to assess the effectiveness of the vaccines and their effect on the prevalence of RV genotypes.

METHODS

Fecal samples were collected from outpatients with RV gastroenteritis in a pediatric clinic in Sapporo, Japan, from 2010 to 2016. GPI genotypes were determined using reverse-transcription polymerase chain reaction. Clinical information and immunization records were obtained from outpatients after 2013. GPI genotypes and clinical features were compared between patients with and without a RV vaccine history.

RESULTS

In total, 270 cases were genotyped. G1P[8]I1 (Wa-like G1P[8]) strains were dominant from 2010 to 2012. G1P[8]I2 (DS-1-like G1P[8]) strains appeared in 2012 and dominated in 2013 to 2015. G2P[4]I2 and G9P[8]I1 strains increased every 3 years (G2P[4]I2: 2011 and 2014, G9P[8]I1: 2010, 2013 and 2016). After the 2013 season, 137 cases were collected, 24 of which were vaccinated. Cases requiring drip infusion were fewer in the vaccination group than in the non-vaccination group (16.7% vs 52.2%). No patients required hospitalization in the vaccination group compared with 10.6% in the non-vaccination group. A severe Vesikari score was less common in the vaccination group than in the non-vaccination group (33.3% vs 78.8%). There was no significant difference in the GPI genotype distribution between the two groups.

CONCLUSION

Rotaviruses vaccine effectiveness, regardless of GPI genotype, was confirmed in terms of alleviation of disease severity.

Full genome characterization of novel DS-1-like G9P[8] rotavirus strains that have emerged in Thailand

The emergence and rapid spread of unusual DS-1-like intergenogroup reassortant rotaviruses having G1/3/8 genotypes have been recently reported from major parts of the world (Africa, Asia, Australia, Europe, and the Americas). During rotavirus surveillance in Thailand, three novel intergenogroup reassortant strains possessing the G9P[8] genotype (DBM2017-016, DBM2017-203, and DBM2018-291) were identified in three stool specimens from diarrheic children. In the present study, we determined and analyzed the full genomes of these three strains. On full-genomic analysis, all three strains were found to share a unique genotype constellation comprising both genogroup 1 and 2 genes: G9-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. Phylogenetic analysis demonstrated that each of the 11 genes of the three strains was closely related to that of emerging DS-1-like intergenogroup reassortant, human, and/or locally circulating human strains. Thus, the three strains were suggested to be multiple reassortants that had acquired the G9-VP7 genes from co-circulating Wa-like G9P[8] rotaviruses in the genetic background of DS-1-like intergenogroup reassortant (likely equine-like G3P[8]) strains. To our knowledge, this is the first description of emerging DS-1-like intergenogroup reassortant strains having the G9P[8] genotype. Our observations will add to the growing insights into the dynamic evolution of emerging DS-1-like intergenogroup reassortant rotaviruses through reassortment.

Whole Genome Analysis of Selected Human Group A Rotavirus Strains Revealed Evolution of DS-1-Like Single- and Double-Gene Reassortant Rotavirus Strains in Pakistan During 2015-2016

Acute gastroenteritis due to group A rotaviruses (RVAs) is the leading cause of infant and childhood morbidity and mortality particularly in developing countries including Pakistan. In this study we have characterized the whole genomes of five RVA strains (PAK56, PAK419, PAK585, PAK622, and PAK663) using the Illumina HiSeq platform. The strains PAK56 and PAK622 exhibited a typical Wa-like genotype constellation (G9-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1 and G3-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1, respectively), whereas PAK419, PAK585, and PAK663 exhibited distinct DS-1-like genotype constellations (G3P[4]-I2-R2-C2-M2-A2-N2-T1-E2-H2, G1P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2, and G3P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2, respectively). Despite their DS-1-like genotype constellation, strain PAK585 possessed the typical Wa-like G1P[8] genotypes, whereas both PAK419 and PAK663 possessed the G3 genotype. In addition, PAK419 also possessed the Wa-like NSP3 genotype T1, suggesting that multiple reassortments have occurred. On Phylogenetic analysis, all of the gene segments of the five strains examined in this study were genetically related to globally circulating human G1, G2, G3, G6, G8, G9, and G12 strains. Interestingly, the NSP2 gene of strain PAK419 showed closest relationship with Indian bovine strain (India/HR/B91), suggesting the occurrence of reassortment between human and bovine RVA strains. Furthermore, strains PAK419, PAK585, and PAK663 were closely related to one another in most of their gene segments, indicating that these strains might have been derived from a common ancestor. To our knowledge this is the first whole genome-based molecular characterization of human rotavirus strains in Pakistan. The results of our study will enhance our existing knowledge on the diversity and evolutionary dynamics of novel RVA strains including DS-1-like intergenogroup reassortant strains spreading in Asian countries including Pakistan, in the pre-vaccine era. Therefore, continuous surveillance is recommended to monitor the evolution, spread and genetic stability of novel reassortant rotavirus strains derived from such events.

Study of Complete Genome Sequences of Rotavirus A Epidemics and Evolution in Japan in 2012-2014

A comprehensive molecular epidemiological study using next-generation sequencing technology was conducted on 333 rotavirus A (RVA)-positive specimens collected from six sentinel hospitals across Japan over three consecutive seasons (2012–2014). The majority of the RVA isolates were grouped into five genotype constellations: Wa-like G1P[8], DS-1-like G1P[8], G2P[4], G3P[8] and G9P[8]. Phylogenetic analysis showed that the distribution of strains varied by geographical locations and epidemic seasons. The VP7 genes of different G types were estimated to evolve at 7.26 × 10^-4–1.04 × 10^-3 nucleotide substitutions per site per year. The Bayesian time-scaled tree of VP7 showed that the time to the most recent common ancestor of epidemic strains within a region was 1–3 years, whereas that of the epidemic strains across the country was 2–6 years. This study provided, for the first time, the timeframe during which an epidemic strain spread locally and within the country and baseline information needed to predict how rapidly RVAs spread.

Characterization of unusual DS-1-like G3P[8] rotavirus strains in children with diarrhea in Japan

The emergence and rapid spread of novel DS-1-like intergenogroup reassortant rotaviruses having the equine-like G3 genotype (DS-1-like G3P[8] strains) have been recently reported from several countries. During rotavirus surveillance in Japan in 2015-2016, three DS-1-like G3P[8] strains were identified from children with severe diarrhea. In the present study, we sequenced and characterized the full genomes of these three strains. On full-genomic analysis, all three strains showed a unique genotype constellation including both genogroup 1 and 2 genes: G3-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. Phylogenetic analysis revealed that each of the 11 genes of the three strains was closely related to that of Japanese DS-1-like G1P[8] and/or Japanese equine-like G3P[4] human strains. Thus, the three study strains were suggested to be reassortants that acquired the G3-VP7 gene from equine G3 rotaviruses on the genetic background of DS-1-like G1P[8] strains. Our observations will provide important insights into the evolutionary dynamics of emerging DS-1-like G3P[8] strains.

Emergence of Double- and Triple-Gene Reassortant G1P[8] Rotaviruses Possessing a DS-1-Like Backbone after Rotavirus Vaccine Introduction in Malawi

To combat the high burden of rotavirus gastroenteritis, multiple African countries have introduced rotavirus vaccines into their childhood immunization programs. Malawi incorporated a G1P[8] rotavirus vaccine (Rotarix) into its immunization schedule in 2012. Utilizing a surveillance platform of hospitalized rotavirus gastroenteritis cases, we examined the phylodynamics of G1P[8] rotavirus strains that circulated in Malawi before (1998 to 2012) and after (2013 to 2014) vaccine introduction. Analysis of whole genomes obtained through next-generation sequencing revealed that all randomly selected prevaccine G1P[8] strains sequenced (n = 32) possessed a Wa-like genetic constellation, whereas postvaccine G1P[8] strains (n = 18) had a DS-1-like constellation. Phylodynamic analyses indicated that postvaccine G1P[8] strains emerged through reassortment events between human Wa- and DS-1-like rotaviruses that circulated in Malawi from the 1990s and hence were classified as atypical DS-1-like reassortants. The time to the most recent common ancestor for G1P[8] strains was from 1981 to 1994; their evolutionary rates ranged from 9.7 × 10⁻⁴ to 4.1 × 10⁻³ nucleotide substitutions/site/year. Three distinct G1P[8] lineages chronologically replaced each other between 1998 and 2014. Genetic drift was the likely driver for lineage turnover in 2005, whereas replacement in 2013 was due to reassortment. Amino acid substitution within the outer glycoprotein VP7 of G1P[8] strains had no impact on the structural conformation of the antigenic regions, suggesting that it is unlikely that they would affect recognition by vaccine-induced neutralizing antibodies. While the emergence of DS-1-like G1P[8] rotavirus reassortants in Malawi was therefore likely due to natural genotype variation, vaccine effectiveness against such strains needs careful evaluation.

IMPORTANCE The error-prone RNA-dependent RNA polymerase and the segmented RNA genome predispose rotaviruses to genetic mutation and genome reassortment, respectively. These evolutionary mechanisms generate novel strains and have the potential to lead to the emergence of vaccine escape mutants. While multiple African countries have introduced a rotavirus vaccine, there are few data describing the evolution of rotaviruses that circulated before and after vaccine introduction. We report the emergence of atypical DS-1-like G1P[8] strains during the postvaccine era in Malawi. Three distinct G1P[8] lineages circulated chronologically from 1998 to 2014; mutation and reassortment drove lineage turnover in 2005 and 2013, respectively. Amino acid substitutions within the outer capsid VP7 glycoprotein did not affect the structural conformation of mapped antigenic sites, suggesting a limited effect on the recognition of G1-specific vaccine-derived antibodies. The genes that constitute the remaining genetic backbone may play important roles in immune evasion, and vaccine effectiveness against such atypical strains needs careful evaluation.

Phylogenetic comparison of the VP7, VP4, VP6, and NSP4 genes of rotaviruses isolated from children in Nizhny Novgorod, Russia, 2015-2016, with cogent genes of the Rotarix and RotaTeq vaccine strains

Group A rotaviruses (RVA) are one of the leading causes of gastroenteritis in young children worldwide. The introduction of universal mass vaccination around the world has contributed to a reduction in hospitalizations and outpatient visits associated with rotavirus infection. Continued surveillance of RVA strains is needed to determine long-term effects of vaccine introduction. In the present work, we carried out the analysis of the genotypic diversity of RVA strains isolated in Nizhny Novgorod (Russia) during the 2015-2016 epidemic season. Also we conducted a comparative analysis of the amino acid sequences of T-cell epitopes of wild-type and vaccine (RotaTeq and Rotarix) strains. In total, 1461 samples were examined. RVAs were detected in 30.4% of cases. Rotaviruses with genotype G9P[8] (40.5%) dominated in the 2015-16 epidemic season. Additionally, RVAs with the following genotypes were detected: G4P[8] (25.4%), G1P[8] (13%), G2P[4] (3.2%). Rotaviruses with genotypes G3P[9], G6P[9], and G1P[9] totaled 3%. The number of partially typed and untyped RVA samples was 66 (14.9%). The findings of a RVA of G6P[9] genotype in Russia were an original observation. Our analysis of VP6 and NSP4 T-cell epitopes showed highly conserved amino acid sequences. The found differences seem not to be caused by the immune pressure but were rather related to the genotypic affiliations of the proteins. Vaccination against rotavirus infection is not included in the national vaccination schedule in Russia. Monitoring of the genotypic and antigenic diversity of contemporary RVA will allow providing a comparative analysis of wild-type strains in areas with and without vaccine campaign.

Distribution of Rotavirus Genotypes from the 2008/2009 to the 2015/2016 Season in Nara Prefecture, Japan

This study was conducted to investigate the distribution of rotavirus genotypes in Nara Prefecture, Japan before and after the introduction of rotavirus vaccination in 2011. Since the 2011/2012 season, DS-1-like G1P[8] strains have been detected in Nara Prefecture, accounting for about half of all strains in the 2014/2015 season. During the 2015/2016 season, no DS-1-like G1P[8] strains were detected; G2P[4] was the predominant genotype.

Detection and molecular characterization of reassortant DS-1-like G1P [8] strains of rotavirus A

Group A rotaviruses (RVA) are the main cause of viral gastroenteritis in children worldwide. In this study we provide the molecular characteristics of reassortant DS-1-like G1P[8] RVA strains detected in Russia for the first time. Previously, such reassortant strains were detected in Japan and Thailand. The G1P[8] RVAs with DS-1-like short electropherotype RNA-PAGE were isolated from children hospitalised with an acute gastroenteritis during the 2013-2014 period. The DS-1-like G1P[8] strains accounted for 2.6% of all RVA strains detected continuously throughout the season. A phylogenetic analysis was made on the basis of the established nucleotide sequences of genes VP7, VP8* (VP4), VP6 and NSP4. The Nizhny Novgorod strains belong to G1-I and G1-II alleles of VP7 gene and to P[8]-3 allele of VP4. According to their VP6 sequences, two Russian samples clustered with the reassortant strains isolated in Japan, Thailand and Australia and two other strains were phylogenetically close to the typical G2P[4] DS-1-like RVA. Nucleotide sequences of G1P[8] strains that belong to NSP4 gene form a separate cluster from G3P[8] DS-1-like rotaviruses detected in Thailand and Australia. The RVA alleles included in Rotarix and RotaTeq vaccine strains were clustered separately from the studied reassortant RVAs. On the grounds of phylogenetic analysis we assume a polyphyletic origin of reassortants between Wa- and DS-1-like strains. Mutation rates evaluated by Bayesian inference in clusters with reassortant RVA strains were 1.004Е-3 (VP7), 1.227E-3 (VP4), 3.909E-4 (VP6), and 4.014Е-4 (NSP4). Analysis of tMRCA showed relatively contemporary origin of alleles DS-1-like G1P[8] rotaviruses: VP7 - 1998 (G1-I) and 1981 (G1-II), VP4 - 1998, VP6 - 1994, NSP4 - 1979.

Changes in Rotavirus Genotypes before and after Vaccine Introduction: a Multicenter, Prospective Observational Study in Three Areas of Japan

In Japan, monovalent and pentavalent rotavirus (RV) vaccines were approved in 2011 and 2012, respectively. To monitor changes in the RV genotypes before and after vaccine introduction, we performed a prospective observational study among children (＜ 5 years) with gastroenteritis who tested RV-positive on antigen rapid tests. Stool samples were collected from 3 different sites in Japan: Tsu City, Mie Prefecture; Kurashiki City, Okayama Prefecture; and Isumi City, Chiba Prefecture. RV genotypes were determined using reverse transcription-polymerase chain reaction. In Tsu City, G3P[8] was dominant (61.0-77.1%) before vaccine introduction, but decreased after introduction. Meanwhile, in an inverse proportion to the decrease in G3P[8], G1P[8] increased until the 2013/14 season, when a sudden predominance of G2P[4] (100%) occurred. A similar trend was observed in Kurashiki City in terms of the extent of reduction in G3P[8] and the emergence of G2P[4]. In Isumi City, G1P[8] was dominant (70.3%) before vaccine introduction, and G9P[8] became predominant (83.3%) in the 2013/14 season. To determine whether the genotype changes are attributable to vaccines or natural epidemiological changes, ongoing continuous monitoring of the RV genotypes is required.

Evolution of DS-1-like G1P[8] double-gene reassortant rotavirus A strains causing gastroenteritis in children in Vietnam in 2012/2013

Rotavirus A (RVA) strains, a leading cause of severe gastroenteritis in children worldwide, commonly possess the Wa or DS-1 genotype constellations. During a hospital-based study conducted in Hanoi, Vietnam, in the 2012-2013 rotavirus season, G1P[8] strains with a virtually identical short RNA migration pattern were detected in 20 (14%) of 141 rotavirus-positive samples. Two representatives of these strains were shown by whole-genome sequencing to be double-gene reassortants possessing the genotype constellation of G1-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. Sequencing and a database search revealed that these Vietnamese G1P[8] double-gene reassortant strains shared an immediate ancestor with a locally circulating G2P[4] strain in all of the inner-capsid and non-structural protein genes, whereas they were more closely related in the VP7 and VP4 genes to a Chinese G1P[8] strain and a Chinese G3P[8] strain, respectively, than to locally circulating G1P[8] strains. Despite the marked similarity between Japanese and Thai G1P[8] double-gene reassortant strains, phylogenetic analysis suggested that the Vietnamese and Japanese/Thai G1P[8] double-gene reassortant strains originated from independent reassortment events. Clinically, children infected with Vietnamese G1P[8] double-gene reassortant strains experienced severe diarrhoea, but it was not more severe than that in children infected with ordinary G1P[8] strains. In conclusion, Vietnamese G1P[8] double-gene reassortant strains originated from a locally circulating G2P[4] strain and caused severe diarrhoea, but there was no evidence of increased virulence.

Full Genome Characterization of Novel DS-1-Like G8P[8] Rotavirus Strains that Have Emerged in Thailand: Reassortment of Bovine and Human Rotavirus Gene Segments in Emerging DS-1-Like Intergenogroup Reassortant Strains

The emergence and rapid spread of unusual DS-1-like intergenogroup reassortant rotavirus strains have been recently reported in Asia, Australia, and Europe. During rotavirus surveillance in Thailand in 2013-2014, novel DS-1-like intergenogroup reassortant strains having G8P[8] genotypes (i.e., strains KKL-17, PCB-79, PCB-84, PCB-85, PCB-103, SKT-107, SWL-12, NP-130, PCB-656, SKT-457, SSKT-269, and SSL-55) were identified in stool samples from hospitalized children with severe diarrhea. In this study, we determined and characterized the complete genomes of these 12 strains (seven strains, KKL-17, PCB-79, PCB-84, PCB-85, PCB-103, SKT-107, and SWL-12, found in 2013 (2013 strains), and five, NP-130, PCB-656, SKT-457, SSKT-269, and SSL-55, in 2014 (2014 strains)). On full genomic analysis, all 12 strains showed a unique genotype constellation comprising a mixture of genogroup 1 and 2 genes: G8-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. With the exception of the G genotype, the unique genotype constellation of the 12 strains (P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2) was found to be shared with DS-1-like intergenogroup reassortant strains. On phylogenetic analysis, six of the 11 genes of the 2013 strains (VP4, VP2, VP3, NSP1, NSP3, and NSP5) appeared to have originated from DS-1-like intergenogroup reassortant strains, while the remaining four (VP7, VP6, VP1, and NSP2) and one (NSP4) gene appeared to be of bovine and human origin, respectively. Thus, the 2013 strains appeared to be reassortant strains as to DS-1-like intergenogroup reassortant, bovine, bovine-like human, and/or human rotaviruses. On the other hand, five of the 11 genes of the 2014 strains (VP4, VP2, VP3, NSP1, and NSP3) appeared to have originated from DS-1-like intergenogroup reassortant strains, while three (VP7, VP1, and NSP2) and one (NSP4) were assumed to be of bovine and human origin, respectively. Notably, the remaining two genes, VP6 and NSP5, of the 2014 strains appeared to have originated from locally circulating DS-1-like G2P[4] human rotaviruses. Thus, the 2014 strains were assumed to be multiple reassortment strains as to DS-1-like intergenogroup reassortant, bovine, bovine-like human, human, and/or locally circulating DS-1-like G2P[4] human rotaviruses. Overall, the great genomic diversity among the DS-1-like intergenogroup reassortant strains seemed to have been generated through additional reassortment events involving animal and human strains. Moreover, all the 11 genes of three of the 2014 strains, NP-130, PCB-656, and SSL-55, were very closely related to those of Vietnamese DS-1-like G8P[8] strains that emerged in 2014-2015, indicating the derivation of these DS-1-like G8P[8] strains from a common ancestor. To our knowledge, this is the first report on full genome-based characterization of DS-1-like G8P[8] strains that have emerged in Thailand. Our observations will add to our growing understanding of the evolutionary patterns of emerging DS-1-like intergenogroup reassortant strains.

Detection of a novel equine-like G3 rotavirus associated with acute gastroenteritis in Brazil

Genotype G3P[8] of rotavirus A (RVA) is detected worldwide, usually associated with Wa-like constellation and exhibiting a long RNA migration pattern. More recently, a novel inter-genogroup, G3P[8] reassortant variant with a short electropherotype, has emerged in Asia, Oceania and Europe, denoting an overall potential of unusual rotavirus strains. During a RVA surveillance in Brazil, G3P[8] strains were found displaying a short electropherotype pattern, which had not been detected before in this region. This study aims to characterize the complete genome of 10 G3P[8] strains detected in the northern region of Brazil. All G3P[8] samples were subjected to partial sequencing, and the whole-genome phylogenetic analysis demonstrated that all strains possessed I2-R2-C2-M2-A2-N1-T2-E2-H2 genotype background, representing reassortants with an equine-like G3 VP7 and amino acid changes in VP4 and VP7 antigenic regions as compared to vaccine strains. Phylogenetic analysis demonstrated high nucleotide identity in almost all RNA segments of G3P[8] DS-1 samples detected in Asia, Oceania and Europe as well as G3P[4] strains in Japan. This study reports a novel, equine-like G3P[8] strain circulating in Brazil and isolated from children hospitalized for severe gastroenteritis, and highlights the complex dynamics of RVA molecular epidemiology. Our findings point to a novel RVA strain emerging in this region, and studies should be done to detect whether this may represent a challenge to current vaccine strategies.

Predominant prevalence of human rotaviruses with the G1P[8] and G8P[8] genotypes with a short RNA profile in 2013 and 2014 in Sukhothai and Phetchaboon provinces, Thailand

Of 2,754 stool specimens collected from children with acute gastroenteritis during 2013-2014 in Sukhothai and Phetchaboon provinces, Thailand, 666 (24.2%) were positive for rotavirus A (RVA) in polyacrylamide gel electrophoresis (PAGE). The G and P types of all RVA-positive specimens were determined by semi-nested RT-PCR. G1P[8] (56.5%) was most prevalent, followed by G2P[4] (22.1%). Unusual G8P[8] human RVAs (HuRVAs) were detected at a high frequency (20.0%). Interestingly, 171 of the 376 G1P[8] HuRVAs and all of the 133 G8P[8] HuRVAs showed a short RNA pattern in PAGE. Thus, it was shown that the properties of HuRVAs have been markedly unusual in recent years in Thailand. J. Med. Virol. 89:615-620, 2017. © 2016 Wiley Periodicals, Inc.

Emergence and spread of G3P[8] rotaviruses possessing an equine-like VP7 and a DS-1-like genetic backbone in the Basque Country (North of Spain), 2015

In March 2015, an atypical G3P[8] rotavirus with an equine-like VP7 gene was detected in Gipuzkoa (Basque Country, Spain) and spread contributing significantly to the seasonal epidemic. The strain was identified in fecal samples collected from 68 patients, mainly children from rural and urban settings with acute gastroenteritis, representing 14.9% of the 455 rotavirus strains genotyped between July 2014 and June 2015. Seven patients (10.3%) were hospitalized. Full genome analysis of six of these strains revealed a DS-1-like genotype constellation, G3-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2, and showed that most genome segments shared the highest nucleotide sequence identity with strains isolated in Japan, Thailand, Australia and the Philippines. The strains of Gipuzkoa were similar to novel G3P[8] reassortant rotaviruses with an equine-like VP7 gene and a DS-1-like genetic backbone that emerged in the Asia-Pacific Region in 2013. The study highlights the circulation of these atypical rotaviruses outside the Asia-Pacific Region of origin, and their emergence in a European Region. Due to their unusual genotype constellation, these strains pose a challenge for the rotavirus strain surveillance, since G-/P-typing, the most commonly used classification system, cannot identify this type of intergenogroup reassortants.

Reassortment of Human and Animal Rotavirus Gene Segments in Emerging DS-1-Like G1P[8] Rotavirus Strains

The emergence and rapid spread of novel DS-1-like G1P[8] human rotaviruses in Japan were recently reported. More recently, such intergenogroup reassortant strains were identified in Thailand, implying the ongoing spread of unusual rotavirus strains in Asia. During rotavirus surveillance in Thailand, three DS-1-like intergenogroup reassortant strains having G3P[8] (RVA/Human-wt/THA/SKT-281/2013/G3P[8] and RVA/Human-wt/THA/SKT-289/2013/G3P[8]) and G2P[8] (RVA/Human-wt/THA/LS-04/2013/G2P[8]) genotypes were identified in fecal samples from hospitalized children with acute gastroenteritis. In this study, we sequenced and characterized the complete genomes of strains SKT-281, SKT-289, and LS-04. On whole genomic analysis, all three strains exhibited unique genotype constellations including both genogroup 1 and 2 genes: G3-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 for strains SKT-281 and SKT-289, and G2-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 for strain LS-04. Except for the G genotype, the unique genotype constellation of the three strains (P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2) is commonly shared with DS-1-like G1P[8] strains. On phylogenetic analysis, nine of the 11 genes of strains SKT-281 and SKT-289 (VP4, VP6, VP1-3, NSP1-3, and NSP5) appeared to have originated from DS-1-like G1P[8] strains, while the remaining VP7 and NSP4 genes appeared to be of equine and bovine origin, respectively. Thus, strains SKT-281 and SKT-289 appeared to be reassortant strains as to DS-1-like G1P[8], animal-derived human, and/or animal rotaviruses. On the other hand, seven of the 11 genes of strain LS-04 (VP7, VP6, VP1, VP3, and NSP3-5) appeared to have originated from locally circulating DS-1-like G2P[4] human rotaviruses, while three genes (VP4, VP2, and NSP1) were assumed to be derived from DS-1-like G1P[8] strains. Notably, the remaining NSP2 gene of strain LS-04 appeared to be of bovine origin. Thus, strain LS-04 was assumed to be a multiple reassortment strain as to DS-1-like G1P[8], locally circulating DS-1-like G2P[4], bovine-like human, and/or bovine rotaviruses. Overall, the great genomic diversity among the DS-1-like G1P[8] strains seemed to have been generated through reassortment involving human and animal strains. To our knowledge, this is the first report on whole genome-based characterization of DS-1-like intergenogroup reassortant strains having G3P[8] and G2P[8] genotypes that have emerged in Thailand. Our observations will provide important insights into the evolutionary dynamics of emerging DS-1-like G1P[8] strains and related reassortant ones.

Emergence and Characterization of Unusual DS-1-Like G1P[8] Rotavirus Strains in Children with Diarrhea in Thailand

The emergence and rapid spread of unusual DS-1-like G1P[8] rotaviruses in Japan have been recently reported. During rotavirus surveillance in Thailand, three DS-1-like G1P[8] strains (RVA/Human-wt/THA/PCB-180/2013/G1P[8], RVA/Human-wt/THA/SKT-109/2013/G1P[8], and RVA/Human-wt/THA/SSKT-41/2013/G1P[8]) were identified in stool specimens from hospitalized children with severe diarrhea. In this study, we sequenced and characterized the complete genomes of strains PCB-180, SKT-109, and SSKT-41. On whole genomic analysis, all three strains exhibited a unique genotype constellation including both genogroup 1 and 2 genes: G1-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. This novel genotype constellation is shared with Japanese DS-1-like G1P[8] strains. Phylogenetic analysis revealed that the G/P genes of strains PCB-180, SKT-109, and SSKT-41 appeared to have originated from human Wa-like G1P[8] strains. On the other hand, the non-G/P genes of the three strains were assumed to have originated from human DS-1-like strains. Thus, strains PCB-180, SKT-109, and SSKT-41 appeared to be derived through reassortment event(s) between Wa-like G1P[8] and DS-1-like human rotaviruses. Furthermore, strains PCB-180, SKT-109, and SSKT-41 were found to have the 11-segment genome almost indistinguishable from one another in their nucleotide sequences and phylogenetic lineages, indicating the derivation of the three strains from a common origin. Moreover, all the 11 genes of the three strains were closely related to those of Japanese DS-1-like G1P[8] strains. Therefore, DS-1-like G1P[8] strains that have emerged in Thailand and Japan were assumed to have originated from a recent common ancestor. To our knowledge, this is the first report on whole genome-based characterization of DS-1-like G1P[8] strains that have emerged in an area other than Japan. Our observations will provide important insights into the evolutionary dynamics of emerging DS-1-like G1P[8] rotaviruses.

Epidemiology of gastroenteritis viruses in Japan: Prevalence, seasonality, and outbreak

Acute gastroenteritis has been recognized as one of the most common diseases in humans and continues to be a major public health problem worldwide. Several groups of viruses have been reported as the causative agents of acute gastroenteritis, including rotavirus, norovirus, sapovirus, human astrovirus, adenovirus, and an increasing number of others which have been reported more recently. The epidemiology, prevalence, seasonality, and outbreaks of these viruses have been reviewed in a number of studies conducted in Japan over three decades. Rotavirus and norovirus were the two most common viruses detected almost equally in children under 5 years of age who were suffering from acute gastroenteritis. Like many other countries, the main rotavirus strains circulating in pediatric patients in Japan are G1P[8], G2P[4], G3P[8], and G9P[8]. Norovirus GII.4 was involved in most outbreaks in Japan and found to be associated with the emergence of new variants Sydney_2012. The classic human astrovirus, MLB, and VA clades astroviruses were also commonly found in pediatric patients with acute diarrhea. The sapovirus and adenovirus have been identified as the minor viral causative agents for acute gastroenteritis in Japan.

A food-borne outbreak of gastroenteritis due to genotype G1P[8] rotavirus among adolescents in Japan

Six high school students in Tochigi prefecture, Japan, developed gastroenteritis after eating at a pork cutlet shop. Molecular epidemiologic analyses showed that the causative agent was genotype G1P[8] rotavirus (RV), this being detected in stool samples from both the patients and the asymptomatic food handlers. The detected RV strains were closely related genetically. The only uncooked food that all victims had eaten was raw sliced cabbage. These findings results suggest that uncooked foods contaminated with RV may be sources of infectious gastroenteritis in adolescents.

Gastroenteritis outbreaks caused by a DS-1-like G1P[8] rotavirus strain, Japan, 2012-2013

Rotavirus A (RVA) genotype G1P[8], a hallmark of the Wa-like strain, typically contains only genotype 1 genes. However, an unusual RVA G1P[8] with genotype 2 genes was recently detected in Japan. We determined the complete genomic constellation of this RVA. Our findings suggest that mixed RVAs may be more competitive than once thought.

Human G3P[9] rotavirus strains possessing an identical genotype constellation to AU-1 isolated at high prevalence in Brazil, 1997-1999

Rotavirus (RV) A is a very common cause of acute diarrhoea in infants and young children worldwide. Most human strains are classified into two major Wa-like and DS-1-like genotype constellations, whilst a minor third strain, AU-1, was described in 1989 among human RV isolates from Japan. AU-1 demonstrates a high degree of homology to a feline RV, FRV-1, which suggests interspecies transmission of feline RV. However, there has been no subsequent report of RVs possessing the AU-1 genotype throughout all 11 genes of the genome. Between March 1997 and December 1999, 157 RV-positive stool samples were collected from Brazilian children, and 16 of the RVs (10.2 %) were P[9] genotype. We analysed eight strains by almost full-genome sequencing. These eight strains were divided into two groups: five AU-1-like and three Wa-like strains. Four of the five AU-1-like strains had the AU-1-like genotype constellation throughout the 11 genes. The remaining AU-1-like strain was considered to be a reassortant strain comprosed of nine, two and one genes from the AU-1-like, Wa-like and G9 strains, respectively. The three Wa-like strains were considered to be reassortants comprising seven to eight genes and three to four genes from Wa-like and non-Wa-like strains, respectively. This report of human G3P[9] RV strains possessing the AU-1 genotype constellation throughout all genes demonstrates the stability and infectivity of the AU-1-like strain with its original genotype over distance and time.

Review of global rotavirus strain prevalence data from six years post vaccine licensure surveillance: is there evidence of strain selection from vaccine pressure?

Comprehensive reviews of pre licensure rotavirus strain prevalence data indicated the global importance of six rotavirus genotypes, G1P[8], G2P[4], G3P[8], G4P[8], G9P[8] and G12P[8]. Since 2006, two vaccines, the monovalent Rotarix (RV1) and the pentavalent RotaTeq (RV5) have been available in over 100 countries worldwide. Of these, 60 countries have already introduced either RV1 or RV5 in their national immunization programs. Post licensure vaccine effectiveness is closely monitored worldwide. This review aimed at describing the global changes in rotavirus strain prevalence over time. The genotype distribution of the nearly 47,000 strains that were characterized during 2007-2012 showed similar picture to that seen in the preceding period. An intriguing finding was the transient predominance of heterotypic strains, mainly in countries using RV1. Unusual and novel antigen combinations continue to emerge, including some causing local outbreaks, even in vaccinated populations. In addition, vaccine strains have been found in both vaccinated infants and their contacts and there is evidence for genetic interaction between vaccine and wild-type strains. In conclusion, the post-vaccine introduction strain prevalence data do not show any consistent pattern indicative of selection pressure resulting from vaccine use, although the increased detection rate of heterotypic G2P[4] strains in some countries following RV1 vaccination is unusual and this issue requires further monitoring.

Spread and predominance in Japan of novel G1P[8] double-reassortant rotavirus strains possessing a DS-1-like genotype constellation typical of G2P[4] strains

Rotavirus is a major cause of severe gastroenteritis in children <5 years of age worldwide, and two, live attenuated rotavirus vaccines are globally available. As rotavirus vaccines are introduced into national immunization programs, there is an increasing need to monitor circulating wild-type strains. However, few studies have systematically examined their full genotype constellation. This study was therefore undertaken to characterize the whole genotype constellation of circulating rotavirus strains in three widely-separated locations in Japan during the 2012 rotavirus season when rotavirus vaccines became available in the country for the first time. Of 107 rotavirus-positive specimens, 50 (46.7%) strains collected from all three locations possessed an unusual G1-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2 constellation in which a typical G2P[4] strain appeared to have acquired its two surface protein genes from the most common G1P[8] strain. These G1P[8] double-reassortant strains were shown to possess the 11 genome segments virtually indistinguishable from each other in their nucleotide sequences and phylogenetic lineages except for two strains that underwent further intra-genotype reassortment. Successful spread to and predominance in broad locations across Japan of novel rotavirus strains possessing a genotype constellation that was previously thought not to be preferred suggests unexpected genomic flexibility of the genotype constellation.

Molecular epidemiology of contemporary G2P[4] human rotaviruses cocirculating in a single U.S. community: footprints of a globally transitioning genotype

Group A rotaviruses (RVs) remain a leading cause of childhood gastroenteritis worldwide. Although the G/P types of locally circulating RVs can vary from year to year and differ depending upon geographical location, those with G1P[8], G2P[4], G3P[8], G4P[8], G9P[8], and G12P[8] specificities typically dominate. Little is known about the evolution and diversity of G2P[4] RVs and the possible role that widespread vaccine use has had on their increased frequency of detection. To address these issues, we analyzed the 12 G2P[4] RV isolates associated with a rise in RV gastroenteritis cases at Vanderbilt University Medical Center (VUMC) during the 2010-2011 winter season. Full-genome sequencing revealed that the isolates had genotype 2 constellations typical of DS-1-like viruses (G2P[4]-I2-R2-C2-M2-A2-N2-T2-E2-H2). Phylogenetic analyses showed that the genome segments of the isolates were comprised of two or three different subgenotype alleles; this enabled recognition of three distinct clades of G2P[4] viruses that caused disease at VUMC in the 2010-2011 season. Although the three clades cocirculated in the same community, there was no evidence of interclade reassortment. Bayesian analysis of 328 VP7 genes of G2 viruses isolated in the last 39 years indicate that existing G2 VP7 gene lineages continue to evolve and that novel lineages, as represented by the VUMC isolates, are constantly being formed. Moreover, G2 lineages are characteristically shaped by lineage turnover events that introduce new globally dominant strains every 7 years, on average. The ongoing evolution of G2 VP7 lineages may give rise to antigenic changes that undermine vaccine effectiveness in the long term.

IMPORTANCE

Little is known about the diversity of cocirculating G2 rotaviruses and how their evolution may undermine the effectiveness of rotavirus vaccines. To expand our understanding of the potential genetic range exhibited by rotaviruses circulating in postvaccine communities, we analyzed part of a collection of rotaviruses recovered from pediatric patients in the United States from 2010 to 2011. Examining the genetic makeup of these viruses revealed they represented three segregated groups that did not exchange genetic material. The distinction between these three groups may be explained by three separate introductions. By comparing a specific gene, namely, VP7, of the recent rotavirus isolates to those from a collection recovered from U.S. children between 1974 and 1991 and other globally circulating rotaviruses, we were able to reconstruct the timing of events that shaped their ancestry. This analysis indicates that G2 rotaviruses are continuously evolving, accumulating changes in their genetic material as they infect new patients.