Rotavirus Strain Trends in United States, 2009-2016: Results from the National Rotavirus Strain Surveillance System (NRSSS)

Whole-Genome Characterization of Rotavirus G9P[6] and G9P[4] Strains That Emerged after Rotavirus Vaccine Introduction in Mozambique

Mozambique introduced the Rotarix® vaccine into the National Immunization Program in September 2015. Following vaccine introduction, rotavirus A (RVA) genotypes, G9P[4] and G9P[6], were detected for the first time since rotavirus surveillance programs were implemented in the country. To understand the emergence of these strains, the whole genomes of 47 ELISA RVA positive strains detected between 2015 and 2018 were characterized using an Illumina MiSeq-based sequencing pipeline. Of the 29 G9 strains characterized, 14 exhibited a typical Wa-like genome constellation and 15 a DS-1-like genome constellation. Mostly, the G9P[4] and G9P[6] strains clustered consistently for most of the genome segments, except the G- and P-genotypes. For the G9 genotype, the strains formed three different conserved clades, separated by the P type (P[4], P[6] and P[8]), suggesting different origins for this genotype. Analysis of the VP6-encoding gene revealed that seven G9P[6] strains clustered close to antelope and bovine strains. A rare E6 NSP4 genotype was detected for strain RVA/Human-wt/MOZ/HCN1595/2017/G9P[4] and a genetically distinct lineage IV or OP354-like P[8] was identified for RVA/Human-wt/MOZ/HGJM0644/2015/G9P[8] strain. These results highlight the need for genomic surveillance of RVA strains detected in Mozambique and the importance of following a One Health approach to identify and characterize potential zoonotic strains causing acute gastroenteritis in Mozambican children.

Culture of Human Rotaviruses in Relevant Models Shows Differences in Culture-Adapted and Nonculture-Adapted Strains

Rotavirus (RV) is the leading cause of acute gastroenteritis (AGE) in children under 5 years old worldwide, and several studies have demonstrated that histo-blood group antigens (HBGAs) play a role in its infection process. In the present study, human stool filtrates from patients diagnosed with RV diarrhea (genotyped as P[8]) were used to infect differentiated Caco-2 cells (dCaco-2) to determine whether such viral strains of clinical origin had the ability to replicate in cell cultures displaying HBGAs. The cell culture-adapted human RV Wa model strain (P[8] genotype) was used as a control. A time-course analysis of infection was conducted in dCaco-2 at 1, 24, 48, 72, and 96 h. The replication of two selected clinical isolates and Wa was further assayed in MA104, undifferentiated Caco-2 (uCaco-2), HT29, and HT29-M6 cells, as well as in monolayers of differentiated human intestinal enteroids (HIEs). The results showed that the culture-adapted Wa strain replicated more efficiently in MA104 cells than other utilized cell types. In contrast, clinical virus isolates replicated more efficiently in dCaco-2 cells and HIEs. Furthermore, through surface plasmon resonance analysis of the interaction between the RV spike protein (VP8*) and its glycan receptor (the H antigen), the V7 RV clinical isolate showed 45 times better affinity compared to VP8* from the Wa strain. These findings support the hypothesis that the differences in virus tropism between clinical virus isolates and RV Wa could be a consequence of the different HBGA contents on the surface of the cell lines employed. dCaco-2, HT29, and HT29M6 cells and HIEs display HBGAs on their surfaces, whereas MA104 and uCaco-2 cells do not. These results indicate the relevance of using non-cell culture-adapted human RV to investigate the replication of rotavirus in relevant infection models.

Evaluation of Three Candidate Live-Attenuated Salmonella enterica Serovar Typhimurium Vaccines to Prevent Non-Typhoidal Salmonella Infection in an Infant Mouse Model

Nontyphoidal Salmonella enterica (NTS) is a leading cause of foodborne illness worldwide, including in the United States, where infants show the highest incidence amongst all age groups. S. enterica serovar Typhimurium is one of the most frequently isolated serovars from NTS infections. We have developed several candidate live-attenuated S. Typhimurium vaccines to prevent NTS infection. The goal of the current study was to assess three live S. Typhimurium vaccine strains (CVD 1921, CVD 1921 ∆htrA and CVD 1926, which have two, three and four gene deletions, respectively) with various levels of reactogenicity and immunogenicity in infant BALB/c mice to predict how they would perform following peroral immunization of infants. We first tested intranasal immunization of 14-day-old mice with three doses delivered at 1-week intervals and evaluated antibody responses and protection against lethal infection with wild-type S. Typhimurium. The vaccines were administered to 14-day-old mice via the peroral route at 1- or 2-week intervals and to 28-day-old mice at 2-week intervals. The three vaccine strains were immunogenic following intranasal immunization of infant mice with vaccine efficacies of 80% (CVD 1921), 63% (CVD 1921 ∆htrA) and 31% (CVD 1926). In contrast, peroral immunization of 14-day-old mice yielded much poorer protection against lethal infection and only immunization of 28-day-old mice at 2-week intervals showed similar protective capacity as intranasal administration (CVD 1921: 83%, CVD 1921 ∆htrA: 43% and CVD 1926: 58%). CVD 1921 was consistently more protective than both CVD 1921 ∆htrA and CVD 1926, regardless of the route of vaccination, immunization schedule and age of mice. Anti-LPS serum IgG responses were similar between the three strains and did not correlate with protection. Due to previously observed reactogenicity of CVD 1921, CVD 1921 ∆htrA and CVD 1926 are our preferred vaccines, but these data show that further improvements would need to be made to achieve suitable protection in young infants when using peroral immunization.

Molecular epidemiology of rotavirus among children in Western Canada: Dynamic changes in genotype prevalence in four consecutive seasons

Rotavirus molecular surveillance remains important in the postvaccine era to monitor the changes in transmission patterns, identify vaccine-induced antigenic changes and discover potentially pathogenic vaccine-related strains. The Canadian province of Alberta introduced rotavirus vaccination into its provincial vaccination schedule in June 2015. To evaluate the impact of this program on stool rotavirus positivity rate, strain diversity, and seasonal trends, we analyzed a prospective cohort of children with acute gastroenteritis recruited between December 2014 and August 2018. We identified dynamic changes in rotavirus positivity and genotype trends during pre- and post-rotavirus vaccine introduction periods. Genotypes G9P[8], G1P[8], G2P[4], and G12P[8] predominated consecutively each season with overall lower rotavirus incidence rates in 2016 and 2017. The demographic and clinical features of rotavirus gastroenteritis were comparable among wild-type rotaviruses; however, children with G12P[8] infections were older (p < 0.001). Continued efforts to monitor changes in the molecular epidemiology of rotavirus using whole genome sequence characterization are needed to further understand the impact of the selection pressure of vaccination on rotavirus evolution.