Emergence of human G2P[4] rotaviruses containing animal derived gene segments in the post-vaccine era

Equine Rotavirus A under the One Health Lens: Potential Impacts on Public Health

Group A rotaviruses are a well-known cause of viral gastroenteritis in infants and children, as well as in many mammalian species and birds, affecting them at a young age. This group of viruses has a double-stranded, segmented RNA genome with high genetic diversity linked to point mutations, recombination, and, importantly, reassortment. While initial molecular investigations undertaken in the 1900s suggested host range restriction among group A rotaviruses based on the fact that different gene segments were distributed among different animal species, recent molecular surveillance and genome constellation genotyping studies conducted by the Rotavirus Classification Working Group (RCWG) have shown that animal rotaviruses serve as a source of diversification of human rotavirus A, highlighting their zoonotic potential. Rotaviruses occurring in various animal species have been linked with contributing genetic material to human rotaviruses, including horses, with the most recent identification of equine-like G3 rotavirus A infecting children. The goal of this article is to review relevant information related to rotavirus structure/genomic organization, epidemiology (with a focus on human and equine rotavirus A), evolution, inter-species transmission, and the potential zoonotic role of equine and other animal rotaviruses. Diagnostics, surveillance and the current status of human and livestock vaccines against RVA are also reviewed.

Genome analyses of species A rotavirus isolated from various mammalian hosts in Northern Ireland during 2013-2016

Rotavirus group A (RVA) is the most important cause of acute diarrhoea and severe dehydration in young mammals. Infection in livestock is associated with significant mortality and economic losses and, together with wildlife reservoirs, acts as a potential source of zoonotic transmission. Therefore, molecular surveillance of circulating RVA strains in animal species is necessary to assess the risks posed to humans and their livestock. An RVA molecular epidemiological surveillance study on clinically diseased livestock species revealed high prevalence in cattle and pigs (31 per cent and 18 per cent, respectively) with significant phylogenetic diversity including a novel and divergent ovine artiodactyl DS-1-like constellation G10-P[15]-I2-R2-C2-M2-A11-N2-T6-E2-H3. An RVA gene reassortment occurred in an RVA asymptomatic pig and identified as a G5-P[13] strain, and a non-structural protein (NSP)2 gene had intergenomically reassorted with a human RVA strain (reverse zoonosis) and possessed a novel NSP4 enterotoxin E9 which may relate to the asymptomatic RVA infection. Analysis of a novel sheep G10-P[15] strain viral protein 4 gene imparts a putative homologous intergenic and interspecies recombination event, subsequently creating the new P[15] divergent lineage. While surveillance across a wider range of wildlife and exotic species identified generally negative or low prevalence, a novel RVA interspecies transmission in a non-indigenous pudu deer (zoo origin) with the constellation of G6-P[11]12-R2-C2-M2-A3-N2-T6-E2-H3 was detected at a viral load of 11.1 log10 copies/gram. The detection of novel emerging strains, interspecies reassortment, interspecies infection, and recombination of RVA circulating in animal livestock and wildlife reservoirs is of paramount importance to the RVA epidemiology and evolution for the One Health approach and post-human vaccine introduction era where highly virulent animal RVA genotypes have the potential to be zoonotically transmitted.

Effect of rotavirus genetic diversity on vaccine impact

Group A rotaviruses (RVAs) are the leading cause of gastroenteritis, causing 0.2 million deaths and several million hospitalisations globally each year. Four rotavirus vaccines (Rotarix^TM , RotaTeq^TM , Rotavac^® and ROTASIIL^® ) have been pre-qualified by the World Health Organization (WHO), but the two newly pre-qualified vaccines (Rotavac^® and ROTASIIL^® ) are currently only in use in Palestine and India, respectively. In 2009, WHO strongly proposed that rotavirus vaccines be included in the routine vaccination schedule of all countries around the world. By the end of 2019, a total of 108 countries had administered rotavirus vaccines, and 10 countries have currently been approved by Gavi for the introduction of rotavirus vaccine in the near future. With 39% of global coverage, rotavirus vaccines have had a substantial effect on diarrhoeal morbidity and mortality in different geographical areas, although efficacy appears to be higher in high income settings. Due to the segmented RNA genome, the pattern of RVA genotypes in the human population is evolving through interspecies transmission and/or reassortment events for which the vaccine might be less effective in the future. However, despite the relative increase in some particular genotypes after rotavirus vaccine use, the overall efficacy of rotavirus mass vaccination worldwide has not been affected. Some of the challenges to improve the effect of current rotavirus vaccines can be solved in the future by new rotavirus vaccines and by vaccines currently in progress.

Rotavirus A Genome Segments Show Distinct Segregation and Codon Usage Patterns

Reassortment of the Rotavirus A (RVA) 11-segment dsRNA genome may generate new genome constellations that allow RVA to expand its host range or evade immune responses. Reassortment may also produce phylogenetic incongruities and weakly linked evolutionary histories across the 11 segments, obscuring reassortment-specific epistasis and changes in substitution rates. To determine the co-segregation patterns of RVA segments, we generated time-scaled phylogenetic trees for each of the 11 segments of 789 complete RVA genomes isolated from mammalian hosts and compared the segments’ geodesic distances. We found that segments 4 (VP4) and 9 (VP7) occupied significantly different tree spaces from each other and from the rest of the genome. By contrast, segments 10 and 11 (NSP4 and NSP5/6) occupied nearly indistinguishable tree spaces, suggesting strong co-segregation. Host-species barriers appeared to vary by segment, with segment 9 (VP7) presenting the weakest association with host species. Bayesian Skyride plots were generated for each segment to compare relative genetic diversity among segments over time. All segments showed a dramatic decrease in diversity around 2007 coinciding with the introduction of RVA vaccines. To assess selection pressures, codon adaptation indices and relative codon deoptimization indices were calculated with respect to different host genomes. Codon usage varied by segment with segment 11 (NSP5) exhibiting significantly higher adaptation to host genomes. Furthermore, RVA codon usage patterns appeared optimized for expression in humans and birds relative to the other hosts examined, suggesting that translational efficiency is not a barrier in RVA zoonosis.

Reverse Genetics Approach for Developing Rotavirus Vaccine Candidates Carrying VP4 and VP7 Genes Cloned from Clinical Isolates of Human Rotavirus

Species A rotaviruses (RVs) are a leading cause of severe acute gastroenteritis in infants and children younger than 5 years. Currently available RV vaccines were adapted from wild-type RV strains by serial passage of cultured cells or by reassortment between human and animal RV strains. These traditional methods require large-scale screening and genotyping to obtain vaccine candidates. Reverse genetics is a tractable, rapid, and reproducible approach to generating recombinant RV vaccine candidates carrying any VP4 and VP7 genes that provide selected antigenicity. Here, we developed a vaccine platform by generating recombinant RVs carrying VP4 (P[4] and P[8]), VP7 (G1, G2, G3, G8, and G9), and/or VP6 genes cloned from human RV clinical samples using the simian RV SA11 strain (G3P[2]) as a backbone. Neutralization assays using monoclonal antibodies and murine antisera revealed that recombinant VP4 and VP7 monoreassortant viruses exhibited altered antigenicity. However, replication of VP4 monoreassortant viruses was severely impaired. Generation of recombinant RVs harboring a chimeric VP4 protein for SA11 and human RV gene components revealed that the VP8* fragment was responsible for efficient infectivity of recombinant RVs. Although this system must be improved because the yield of vaccine viruses directly affects vaccine manufacturing costs, reverse genetics requires less time than traditional methods and enables rapid production of safe and effective vaccine candidates.IMPORTANCE Although vaccines have reduced global RV-associated hospitalization and mortality over the past decade, the multisegmented genome of RVs allows reassortment of VP4 and VP7 genes from different RV species and strains. The evolutionary dynamics of novel RV genotypes and their constellations have led to great genomic and antigenic diversity. The reverse genetics system is a powerful tool for manipulating RV genes, thereby controlling viral antigenicity, growth capacity, and pathogenicity. Here, we generated recombinant simian RVs (strain SA11) carrying heterologous VP4 and VP7 genes cloned from clinical isolates and showed that VP4- or VP7-substituted chimeric viruses can be used for antigenic characterization of RV outer capsid proteins and as improved seed viruses for vaccine production.

Multiple Introductions and Antigenic Mismatch with Vaccines May Contribute to Increased Predominance of G12P[8] Rotaviruses in the United States

Rotavirus is the leading global cause of diarrheal mortality for unvaccinated children under 5 years of age. The outer capsid of rotavirus virions consists of VP7 and VP4 proteins, which determine viral G and P types, respectively, and are primary targets of neutralizing antibodies. Successful vaccination depends upon generating broadly protective immune responses following exposure to rotaviruses presenting a limited number of G- and P-type antigens. Vaccine introduction resulted in decreased rotavirus disease burden but also coincided with the emergence of uncommon G and P genotypes, including G12. To gain insight into the recent predominance of G12P[8] rotaviruses in the United States, we evaluated 142 complete rotavirus genome sequences and metadata from 151 clinical specimens collected in Nashville, TN, from 2011 to 2013 through the New Vaccine Surveillance Network. Circulating G12P[8] strains were found to share many segments with other locally circulating strains but to have distinct constellations. Phylogenetic analyses of G12 sequences and their geographic sources provided evidence for multiple separate introductions of G12 segments into Nashville, TN. Antigenic epitopes of VP7 proteins of G12P[8] strains circulating in Nashville, TN, differ markedly from those of vaccine strains. Fully vaccinated children were found to be infected with G12P[8] strains more frequently than with other rotavirus genotypes. Multiple introductions and significant antigenic mismatch may in part explain the recent predominance of G12P[8] strains in the United States and emphasize the need for continued monitoring of rotavirus vaccine efficacy against emerging rotavirus genotypes.IMPORTANCE Rotavirus is an important cause of childhood diarrheal disease worldwide. Two immunodominant proteins of rotavirus, VP7 and VP4, determine G and P genotypes, respectively. Recently, G12P[8] rotaviruses have become increasingly predominant. By analyzing rotavirus genome sequences from stool specimens obtained in Nashville, TN, from 2011 to 2013 and globally circulating rotaviruses, we found evidence of multiple introductions of G12 genes into the area. Based on sequence polymorphisms, VP7 proteins of these viruses are predicted to present themselves to the immune system very differently than those of vaccine strains. Many of the sick children with G12P[8] rotavirus in their diarrheal stools also were fully vaccinated. Our findings emphasize the need for continued monitoring of circulating rotaviruses and the effectiveness of the vaccines against strains with emerging G and P genotypes.

A Multiplex PCR/LDR Assay for Viral Agents of Diarrhea with the Capacity to Genotype Rotavirus

Rotavirus and noroviruses are major causes of diarrhea. Variable rotavirus vaccination efficacy in Africa and Asia is multifactorial, including the diversity of circulating strains and viral co-infection. We describe a multiplexed assay that detects and genotypes viruses from stool specimens. It includes a one-step reverse transcriptase PCR reaction, a ligase detection reaction (LDR), then hybridization of fluorescent products to micro-beads. In clinical samples it detects rotavirus, caliciviruses (sapovirus and norovirus), mixed infections, and genotypes or genogroups of rotaviruses and noroviruses, respectively. The assay also has the capacity to detect hepatitis A. The assay was validated on reference isolates and 296 stool specimens from the US and Ghana. The assay was 97% sensitive and 100% specific. The genogroup was concordant in 100% of norovirus, and the genotype in 91% and 89% of rotavirus G- and P-types, respectively. Two rare rotavirus strains, G6P[6] and G6P[8], were detected in stool specimens from Ghana. The high-throughput assay is sensitive, specific, and may be of utility in the epidemiological surveillance for rare and emerging viral strains post-rotavirus vaccine implementation.

Emergence of Human G2P[4] Rotaviruses in the Post-vaccination Era in South Korea: Footprints of Multiple Interspecies Re-assortment Events

After the introduction of two global rotavirus vaccines, RotaTeq in 2007 and Rotarix in 2008 in South Korea, G1[P8] rotavirus was the major rotavirus genotype in the country until 2012. However, in this study, an emergence of G2P[4] as the dominant genotype during the 2013 to 2015 season has been reported. Genetic analysis revealed that these viruses had typical DS-1-like genotype constellation and showed evidence of re-assortment in one or more genome segments, including the incorporation of NSP4 genes from strains B-47/2008 from a cow and R4/Haryana/2007 from a buffalo in India, and the VP1 and VP3 genes from strain GO34/1999 from a goat in Bangladesh. Compared to the G2 RotaTeq vaccine strain, 17–24 amino acid changes, specifically A87T, D96N, S213D, and S242N substitutions in G2 epitopes, were observed. These results suggest that multiple interspecies re-assortment events might have contributed to the emergence of G2P[4] rotaviruses in the post-vaccination era in South Korea.

Genetic analysis of rotavirus G2P[4] strains in Pune, Western India: circulation of a novel reassortant bearing E6 NSP4 genotype

In India, G2P[4] strains are known to be the second most predominant group A rotaviruses causing acute gastroenteritis among children. This study was performed to determine the diversity within VP7(G), VP4(P), VP6(I) and NSP4(E) genes of 16 G2P[4] rotavirus strains detected in children hospitalized for acute gastroenteritis in Pune, Western India during 2009-2013. Fourteen strains showed G2-P[4]-I2-E2 and two strains showed G2-P[4]-I2-E6 genotype constellation. Phylogenetic analysis showed their clustering into G2-IV-a3, P[4]-5bi/ii, I2-3ii and E2-4i/ii or E6 genotypes/lineages. These data reveal inter- and/or intra-genotypic variations in a genogroup-2 constellation of G2P[4] rotavirus strains circulating in Pune, Western India, providing evidence of a novel G2P[4] reassortant bearing a rare NSP4 genotype, E6 during 2009-2013.