Genetic variation in the VP7 gene of rotavirus G1P[8] strains isolated in Vietnam, 1998-2009

Evolutionary analysis of all eleven genes of species C rotaviruses circulating in humans and domestic animals

Species C rotaviruses (RVC) are the second most common rotavirus species known to cause gastroenteritis in humans and pigs and with occurrence documented in cattle, dogs, ferrets, and sloth bears. Despite the host-specific nature of RVC genotypes, cross-species transmission, reassortment, and recombination events are also documented. In the present study, we inferred the evolutionary history of globally circulating RVC strains, including time scale stasis, the most probable ancestral country, and the most probable source host using Bayesian methods implemented in BEAST v.1.8.4. The human-derived RVC strains were majorly monophyletic and further grouped into two lineages. The RVC strains derived from pigs were monophyletic for the VP1 and the remaining genes were classified into 2 to 4 groups based on the high posterior support. The root mean age for all the genes indicated the circulation of RVC for over 800 years. Overall, the time to Most Recent Common Ancestor of human RVC strains dated back to the beginning of the 20th century. The VP7 and NSP2 genes had the lowest rates of evolution compared to other genes. The majority of the genes of RVC showed their origin in Japan except for VP7 and VP4 genes in South Korea. The phylogeographic analysis with the country as a trait showed the role of Japan, China, and India in the dispersion of the virus. In the current study, significant transmission links between different hosts were analyzed for the first time using the host as a trait. Significant transmission links between pigs and other animal species as well as humans indicate possible transmission from the pig as a source host and suggest monitoring of proximity with animals.

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.

The prevalence and genotype diversity of Human Rotavirus A circulating in Thailand, 2011-2014

Human rotavirus A (RVA) is the major infectious virus causing acute watery diarrhea in children, especially those younger than 5 years of age, and is a major public health problem in Thailand. Outbreaks of this virus have been reported worldwide. Besides the common genotypes, unusual genotypes providing evidence of inter-species transmission have also been described. Therefore, the aim of this study was to investigate the prevalence and genotypes of RVA in Thailand. A total of 688 samples were collected from children who were hospitalized with acute diarrhea in Chumphae Hospital in Khon Kaen and Chulalongkorn Hospital in Bangkok. RVA was detected using one-step RT-PCR and the genotypes were evaluated by sequencing. Overall, 204 of the 688 samples (30%) were positive for RVA. Nine genotypes were identified: three common in humans (G1P[8] [53%], G2P[4] [18%], G3P[8] [12%]), one feline-like (G3P[9] [1%]), four porcine-like (G4P[6] [0.5%], G5P[6] [0.5%], G9P[8] [0.5%], G12P[6] [1.5%]), and one bovine-like (G8P[8] [13%]). The variation in virus genotypes and the animal-like genotypes detected in this study suggested that a high diversity of RVA types is circulating in the Thai population. Therefore, continuous molecular epidemiological monitoring of RVA is essential and has implications for the national vaccination program.

Genome-Wide Evolutionary Analyses of G1P[8] Strains Isolated Before and After Rotavirus Vaccine Introduction

Rotaviruses are the most important etiological agent of acute gastroenteritis in young children worldwide. Among the first countries to introduce rotavirus vaccines into their national immunization programs were Belgium (November 2006) and Australia (July 2007). Surveillance programs in Belgium (since 1999) and Australia (since 1989) offer the opportunity to perform a detailed comparison of rotavirus strains circulating pre- and postvaccine introduction. G1P[8] rotaviruses are the most prominent genotype in humans, and a total of 157 G1P[8] rotaviruses isolated between 1999 and 2011 were selected from Belgium and Australia and their complete genomes were sequenced. Phylogenetic analysis showed evidence of frequent reassortment among Belgian and Australian G1P[8] rotaviruses. Although many different phylogenetic subclusters were present before and after vaccine introduction, some unique clusters were only identified after vaccine introduction, which could be due to natural fluctuation or the first signs of vaccine-driven evolution. The times to the most recent common ancestors for the Belgian and Australian G1P[8] rotaviruses ranged from 1846 to 1955 depending on the gene segment, with VP7 and NSP4 resulting in the most recent estimates. We found no evidence that rotavirus population size was affected after vaccine introduction and only six amino acid sites in VP2, VP3, VP7, and NSP1 were identified to be under positive selective pressure. Continued surveillance of G1P[8] strains is needed to determine long-term effects of vaccine introductions, particularly now rotavirus vaccines are implemented in the national immunization programs of an increasing number of countries worldwide.

G1P[8] species A rotavirus over 27 years--pre- and post-vaccination eras--in Brazil: full genomic constellation analysis and no evidence for selection pressure by Rotarix® vaccine

Epidemiological data on species A rotavirus (RVA) infections have demonstrated the genetic diversity of strains circulating worldwide. Many G and P genotype combinations have been described over the years, varying regionally and temporally, especially in developing countries. However, the most common G and P genotype combinations identified in RVA human strains worldwide are G1P[8], G2P[4], G3P[8], G4P[8] and G9P[8]. RVA genotype G1P[8] strains are responsible for more than 50% of child infections worldwide and component of the two vaccines (Rotarix® [RV1] and RotaTeq® [RV5]) licensed globally. For a better understanding of the evolutionary mechanisms of this genotype in Brazil, phylogenetic analyses based on the 11 RVA genome segments (genomic constellation) from 90 G1P[8] RVA strains collected in two eras - (i) pre-vaccination with RV1 (1996-February 2006); (ii) post-vaccination (March 2006-2013) - in different Brazilian states were performed. The results showed the Wa-like genomic constellation of the Brazilian G1P[8] strains with a I1-R1-C1-M1-A1-N1-T1-E1-H1 specificity, except for two strains (rj14055-07 and ba19030-10) that belong to a I1-R1-C1-M1-A1-N1-T3-E1-H1 genomic constellation, evidencing the occurrence of reassortment (Wa-like×AU-1-like) of the NSP3 gene. Reassortment events were also demonstrated between Brazilian G1P[8] strains and the RV1 vaccine strain in some genes in vaccinated and unvaccinated children. VP7 and VP8* antigenic site analysis showed that the amino acid substitutions observed in samples collected after the introduction of RV1 in Brazil were already detected in samples collected in the 1980s and 1990s, suggesting that mass Brazilian RV1 vaccination had no impact on the diversity observed inside antigenic sites for these two proteins.

Differences in lineage replacement dynamics of G1 and G2 rotavirus strains versus G9 strain over a period of 22 years in Bangladesh

Group A rotaviruses (RVAs) have been a major cause of severe gastroenteritis in Bangladesh, mainly in children below the age of five. At the icddr,b, RVA strains collection and characterization dates back for more than 20 years. This sample collection was used to study the molecular evolution of the VP7 gene of G1, G2 and G9 RVA strains, which have been circulating in Bangladesh for most of this study period. The evolutionary rates (95% HPD) for G1, G2 and G9 were calculated to be 0.93×10(-3) (0.68-1.18), 1.45×10(-3) (1.12-1.78) and 1.07×10(-3) (0.78-1.39), respectively, which is in line with previous data for the RVA VP7 outer capsid protein, which is under strong negative selective pressure. Bayesian analyses revealed that for the G1 and G2 genotypes, one or multiple lineages co-circulated for one or a few seasons, frequently followed by replacement with genetically different lineages. This can be explained by the existence of a large variety of G1 and G2 RVA lineages and the rapid dissemination of different lineages across the globe. In contrast, circulating G9 lineages were rather closely related to each other across the study period and they were usually derived from variants circulating in the previous season(s). This is consistent with the fact that G9 RVAs have circulated in the human population for less than 20 years, and therefore their genetic diversity is much smaller, not resulting in the replacement of circulating G9 strains by highly divergent G9 lineages from abroad. Such different evolutionary dynamics for different RVA genotypes may alter their response to the selective pressure that might be exerted by the introduction of RVA vaccines and therefore a continued close monitoring is warranted.

Characterization of the NSP4 gene of group A human rotavirus G1P[8] strains circulating in Sapporo, Japan from 1987 to 2000

The genetic diversity of the NSP4 gene of rotavirus G1P[8] strains obtained in Sapporo was analyzed, Japan from 1987 to 2000. Sixty-four strains, which were distributed across the whole study period, were included. All G1P[8] NSP4 genes detected in this study belonged to genotype E1, which divided into at least three lineages. The Sapporo rotavirus G1P[8] isolates were found in each lineage. The mean estimated substitution rate was 1.40 × 10(-3) nucleotide substitutions per site per year, which was comparable to that of the G1P[8] VP7 gene. Comparison of the deduced NSP4 amino acid sequences showed genetic diversity at the center of antigenic site II, but not in the enterotoxic domain. This report represents the first investigation of the genetic diversity and evolution of group A rotavirus NSP4 genes in Asia.