Whole Genome Analysis of Human Rotaviruses Reveals Single Gene Reassortant Rotavirus Strains in Zambia

Rotarix^® vaccine was implemented nationwide in Zambia in 2013. In this study, four unusual strains collected in the post-vaccine period were subjected to whole genome sequencing and analysis. The four strains possessed atypical genotype constellations, with at least one reassortant genome segment within the constellation. One of the strains (UFS-NGS-MRC-DPRU4749) was genetically and phylogenetically distinct in the VP4 and VP1 gene segments. Pairwise analyses demonstrated several amino acid disparities in the VP4 antigenic sites of this strain compared to that of Rotarix^®. Although the impact of these amino acid disparities remains to be determined, this study adds to our understanding of the whole genomes of reassortant strains circulating in Zambia following Rotarix^® vaccine introduction.

Whole Genome Characterization and Evolutionary Analysis of G1P[8] Rotavirus A Strains during the Pre- and Post-Vaccine Periods in Mozambique (2012-2017)

Mozambique introduced the Rotarix^® vaccine (GSK Biologicals, Rixensart, Belgium) into the National Immunization Program in September 2015. Although G1P[8] was one of the most prevalent genotypes between 2012 and 2017 in Mozambique, no complete genomes had been sequenced to date. Here we report whole genome sequence analysis for 36 G1P[8] strains using an Illumina MiSeq platform. All strains exhibited a Wa-like genetic backbone (G1-P[8]-I1-R1-C1-M1-A1-N1-T1-E1-H1). Phylogenetic analysis showed that most of the Mozambican strains clustered closely together in a conserved clade for the entire genome. No distinct clustering for pre- and post-vaccine strains were observed. These findings may suggest no selective pressure by the introduction of the Rotarix^® vaccine in 2015. Two strains (HJM1646 and HGM0544) showed varied clustering for the entire genome, suggesting reassortment, whereas a further strain obtained from a rural area (MAN0033) clustered separately for all gene segments. Bayesian analysis for the VP7 and VP4 encoding gene segments supported the phylogenetic analysis and indicated a possible introduction from India around 2011.7 and 2013.0 for the main Mozambican clade. Continued monitoring of rotavirus strains in the post-vaccine period is required to fully understand the impact of vaccine introduction on the diversity and evolution of rotavirus strains.

One-step multiplex real-time RT-PCR assay for detecting and genotyping wild-type group A rotavirus strains and vaccine strains (Rotarix® and RotaTeq®) in stool samples

Background. Group A rotavirus (RVA) infection is the major cause of acute gastroenteritis (AGE) in young children worldwide. Introduction of two live-attenuated rotavirus vaccines, RotaTeq® and Rotarix®, has dramatically reduced RVA associated AGE and mortality in developed as well as in many developing countries. High-throughput methods are needed to genotype rotavirus wild-type strains and to identify vaccine strains in stool samples. Quantitative RT-PCR assays (qRT-PCR) offer several advantages including increased sensitivity, higher throughput, and faster turnaround time. Methods. In this study, a one-step multiplex qRT-PCR assay was developed to detect and genotype wild-type strains and vaccine (Rotarix® and RotaTeq®) rotavirus strains along with an internal processing control (Xeno or MS2 RNA). Real-time RT-PCR assays were designed for VP7 (G1, G2, G3, G4, G9, G12) and VP4 (P[4], P[6] and P[8]) genotypes. The multiplex qRT-PCR assay also included previously published NSP3 qRT-PCR for rotavirus detection and Rotarix® NSP2 and RotaTeq® VP6 qRT-PCRs for detection of Rotarix® and RotaTeq® vaccine strains respectively. The multiplex qRT-PCR assay was validated using 853 sequence confirmed stool samples and 24 lab cultured strains of different rotavirus genotypes. By using thermostable rTth polymerase enzyme, dsRNA denaturation, reverse transcription (RT) and amplification (PCR) steps were performed in single tube by uninterrupted thermocycling profile to reduce chances of sample cross contamination and for rapid generation of results. For quantification, standard curves were generated using dsRNA transcripts derived from RVA gene segments. Results. The VP7 qRT-PCRs exhibited 98.8-100% sensitivity, 99.7-100% specificity, 85-95% efficiency and a limit of detection of 4-60 copies per singleplex reaction. The VP7 qRT-PCRs exhibited 81-92% efficiency and limit of detection of 150-600 copies in multiplex reactions. The VP4 qRT-PCRs exhibited 98.8-100% sensitivity, 100% specificity, 86-89% efficiency and a limit of detection of 12-400 copies per singleplex reactions. The VP4 qRT-PCRs exhibited 82-90% efficiency and limit of detection of 120-4000 copies in multiplex reaction. Discussion. The one-step multiplex qRT-PCR assay will facilitate high-throughput rotavirus genotype characterization for monitoring circulating rotavirus wild-type strains causing rotavirus infections, determining the frequency of Rotarix® and RotaTeq® vaccine strains and vaccine-derived reassortants associated with AGE, and help to identify novel rotavirus strains derived by reassortment between vaccine and wild-type strains.

Characterization of G2P[4] rotavirus strains causing outbreaks of gastroenteritis in the Northern Territory, Australia, in 1999, 2004 and 2009

Outbreaks of rotavirus diarrhea cause a large disease burden in the Alice Springs region of the Northern Territory, Australia. The introduction of the rotavirus vaccine Rotarix® has been associated with an increase in detection of G2P[4] strains in many countries. However, G2P[4] emergence has also been observed in vaccine-naive countries, suggesting a general global increase in the circulation of G2P[4] strains. A G2P[4] rotavirus outbreak occurred in 2009, 28 months after the introduction of the Rotarix® vaccine and 43 children were hospitalized. Pre-vaccine introduction, G2P[4] strains were observed associated with large outbreaks in 1999 and 2004. To determine the genetic relationship between these strains whole genome sequence analysis was conducted on representative strains from each of the G2P[4] outbreaks, in 1999, 2004 and 2009. Phylogenetic analysis revealed the majority of genes from 2009 outbreak strain clustered with contemporary global strains, while the VP7 gene clustered with contemporary and older strains and was antigenically distinct to the majority of contemporary global G2P[4] strains; suggesting the strain was an intragenogroup reassortant. The 1999 and 2009 strains appear to share similar evolutionary origins, and both had a high degree of genetic identity to previously identified Australian and global strains. Conversely, the 2004 outbreak strain was more divergent in comparison to Australian and global strains. The 1999 and 2004 outbreaks likely occurred due to the accumulation of immunologically naïve children in the population following low levels of G2P[4] rotavirus disease in the community in the years prior to each outbreak. The 2009 outbreak was associated with moderate vaccine coverage in the population and vaccine efficacy against the strain was low. The circulation of this unusual strain in the population combined with low vaccine coverage and diminished vaccine efficacy likely contributed to the outbreak occurring in this population.