Genetic stability of rotaviruses recovered from asymptomatic neonatal infections

Human milk oligosaccharides, milk microbiome and infant gut microbiome modulate neonatal rotavirus infection

Neonatal rotavirus infections are predominantly asymptomatic. While an association with gastrointestinal symptoms has been described in some settings, factors influencing differences in clinical presentation are not well understood. Using multidisciplinary approaches, we show that a complex interplay between human milk oligosaccharides (HMOs), milk microbiome, and infant gut microbiome impacts neonatal rotavirus infections. Validating in vitro studies where HMOs are not decoy receptors for neonatal strain G10P[11], population studies show significantly higher levels of Lacto-N-tetraose (LNT), 2'-fucosyllactose (2'FL), and 6'-siallylactose (6'SL) in milk from mothers of rotavirus-positive neonates with gastrointestinal symptoms. Further, these HMOs correlate with abundance of Enterobacter/Klebsiella in maternal milk and infant stool. Specific HMOs also improve the infectivity of a neonatal strain-derived rotavirus vaccine. This study provides molecular and translational insight into host factors influencing neonatal rotavirus infections and identifies maternal components that could promote the performance of live, attenuated rotavirus vaccines.

Diversity in Rotavirus-Host Glycan Interactions: A "Sweet" Spectrum

Interaction with cellular glycans is a critical initial step in the pathogenesis of many infectious agents. Technological advances in glycobiology have expanded the repertoire of studies delineating host glycan-pathogen interactions. For rotavirus, the VP8* domain of the outer capsid spike protein VP4 is known to interact with cellular glycans. Sialic acid was considered the key cellular attachment factor for rotaviruses for decades. Although this is true for many rotavirus strains causing infections in animals, glycan array screens show that many human rotavirus strains bind nonsialylated glycoconjugates, called histo-blood group antigens, in a strain-specific manner. The expression of histo-blood group antigens is determined genetically and is regulated developmentally. Variations in glycan binding between different rotavirus strains are biologically relevant and provide new insights into multiple aspects of virus pathogenesis such as interspecies transmission, host range restriction, and tissue tropism. The genetics of glycan expression may affect susceptibility to different rotavirus strains and vaccine viruses, and impact the efficacy of rotavirus vaccination in different populations. A multidisciplinary approach to understanding rotavirus-host glycan interactions provides molecular insights into the interaction between microbial pathogens and glycans, and opens up new avenues to translate findings from the bench to the human population.

The VP8* domain of neonatal rotavirus strain G10P[11] binds to type II precursor glycans

Naturally occurring bovine-human reassortant rotaviruses with a P[11] VP4 genotype exhibit a tropism for neonates. Interaction of the VP8* domain of the spike protein VP4 with sialic acid was thought to be the key mediator for rotavirus infectivity. However, recent studies have indicated a role for nonsialylated glycoconjugates, including histo-blood group antigens (HBGAs), in the infectivity of human rotaviruses. We sought to determine if the bovine rotavirus-derived VP8* of a reassortant neonatal G10P[11] virus interacts with hitherto uncharacterized glycans. In an array screen of >600 glycans, VP8* P[11] showed specific binding to glycans with the Galβ1-4GlcNAc motif, which forms the core structure of type II glycans and is the precursor of H type II HBGA. The specificity of glycan binding was confirmed through hemagglutination assays; GST-VP8* P[11] hemagglutinates type O, A, and B red blood cells as well as pooled umbilical cord blood erythrocytes. Further, G10P[11] infectivity was significantly enhanced by the expression of H type II HBGA in CHO cells. The bovine-origin VP4 was confirmed to be essential for this increased infectivity, using laboratory-derived reassortant viruses generated from sialic acid binding rotavirus SA11-4F and a bovine G10P[11] rotavirus, B223. The binding to a core glycan unit has not been reported for any rotavirus VP4. Core glycan synthesis is constitutive in most cell types, and modification of these glycans is thought to be developmentally regulated. These studies provide the first molecular basis for understanding neonatal rotavirus infections, indicating that glycan modification during neonatal development may mediate the age-restricted infectivity of neonatal viruses.

Whole-genome consensus sequence analysis of a South African rotavirus SA11 sample reveals a mixed infection with two close derivatives of the SA11-H96 strain

Whole-genome, sequence-independent amplification and 454(®) pyrosequencing of a rotavirus SA11 cell culture sample with an unknown passage history yielded consensus sequences of twelve complete genome segments. Two distinct sequences for genome segment 8 (encoding NSP2) were present, indicating a mixed infection with two rotavirus SA11 strains. The genotypes of the viruses were G3-P[2]-I2-R2-C5-M5-A5-Nx-T5-E2-H5, where x was either 5 or 2. The strains were named RVA/Simian-tc/ZAF/SA11-N5/1958/G3P[2] and RVA/Simian-tc/ZAF/SA11-N2/1958/G3P[2]. The genotype (N2) and sequence of genome segment 8 of RVA/Simian-tc/ZAF/SA11-N2/1958/G3P[2] were identical to that of the bovine rotavirus O agent. Five novel amino acids were detected in minor population variants of three genome segments. Genome segment 1 (VP1) has a high nucleotide substitution rate, but the substitutions are synonymous. Distance matrices and Bayesian molecular clock phylogenetics showed that SA11-N2 is a reassortant containing genome segment 8 from the O agent, whereas SA11-N5 is a very close derivative of the prototype SA11-H96.

Comparison of viral load and duration of virus shedding in symptomatic and asymptomatic neonatal rotavirus infections

A single rotavirus strain causing asymptomatic infections as well as severe gastrointestinal disease has been described in the neonatal nurseries of the Christian Medical College, Vellore. In this study, quantitative real-time RT-PCR was used to determine the association of viral load with the presence of gastrointestinal symptoms in neonates. Viral load was estimated in terms of the crossing point [C(t) value] at which the amplicon could be detected in the real-time PCR assay. The study was carried out on 103 neonates, including 33 asymptomatic neonates and 70 neonates with different gastrointestinal symptoms. The duration of virus shedding was also compared between five symptomatic and four asymptomatic neonates using real-time RT-PCR. There was no significant difference in viral load between symptomatic and asymptomatic neonates (P = 0.087). Among neonates with different gastrointestinal symptoms, those presenting with feed intolerance and abdominal distension had a significantly higher viral load than those with other gastrointestinal symptoms (P = 0.02). For the study on virus shedding, nine neonates were followed up for a median duration of 53 days, with a median of 31 samples tested per child. Extended shedding of low copies of rotavirus was found, with no significant differences in pattern of shedding between symptomatic and asymptomatic neonates. The lack of correlation between viral load and gastrointestinal disease demonstrates yet another difference between neonatal rotavirus infection and infection in older children where higher viral load correlates with severe disease.

Rotavirus infection in the neonatal nurseries of a tertiary care hospital in India

BACKGROUND

The majority of neonatal rotavirus infections are believed to be asymptomatic, and protection from subsequent infection and disease has been reported in neonatally infected children. In this study, we present the results of a 4-year prospective surveillance in the neonatal nurseries of a tertiary care hospital in south India.

METHODS

Stool samples from neonates admitted for >48 hours either with gastrointestinal (GI) symptoms or with nonenteric pathology were screened for rotavirus. Careful assessment of clinical data was carried out. G- and P-typing for all symptomatic rotavirus positive cases and equal number of asymptomatic controls from the same month was determined by reverse transcription polymerase chain reaction.

RESULTS

Rotavirus was detected in 43.9% of 1411 neonates, including those with and without gastrointestinal disease. Rotavirus detection was significantly higher among neonates with GI disease (55.5%) than asymptomatic neonates (44.4%) (P < 0.001). Rotavirus was seen in association with diarrhea, vomiting, feed intolerance, necrotizing enterocolitis, hematochezia, gastroesophageal reflux, and abdominal distension. Diarrhea was significantly more frequent in neonates with rotavirus infection (P < 0.001) whereas uninfected neonates developed significantly more feeding intolerance (P < 0.001). Significantly greater proportion of term neonates with GI disease were positive for rotavirus than preterm neonates (P < 0.001). G10P[11] was the most common genotype associated with both symptomatic and asymptomatic infections.

CONCLUSIONS

This study documents the high rates of rotavirus infection in the neonatal nurseries and the continuing detection of the G10P[11] strain associated with GI disease in Vellore.

Shifts of rotavirus g and p types in Nicaragua--2001-2003

The present study reports the diversity of rotavirus strains circulating in León, Nicaragua during three years. There was a shift of G and P genotypes with increment of one specific genotype during the second most important peak of diarrhea occurring in the beginning of every year.

G3P2 rotaviruses causing diarrhoeal disease in neonates differ in VP4, VP7 and NSP4 sequence from G3P2 strains causing asymptomatic neonatal infection

During longitudinal epidemiological studies of rotavirus infections in children in Melbourne, Australia human G3P2 rotavirus strains causing asymptomatic or symptomatic infections have been identified. Eleven strains (AS strains) associated with asymptomatic infection of newborn babies from 1974-1984, and five strains (S strains) associated with symptomatic infection of newborn babies (4) or a 22 week old infant (1) during 1980-1986 were studied. The entire nucleotide sequences of genes coding for VP4, VP7, NSP4 and VP6 were derived for representative AS and S strains. The nucleotide sequences of neutralization epitope regions present on the outer capsid proteins VP4 and VP7 (regions C and F) showed extensive conservation of nucleotide and deduced amino acid sequence in all strains. Minor variations were observed over the 12 year period in VP7 epitope regions A and B in some strains. Specific conserved amino acids differences between the asymptomatic and symptomatic strains were observed in the genes encoding VP4 at aa133 and 303 (asparagine or threonine) and 380 (serine or isoleucine), VP7 at aa27 (threonine or isoleucine), aa29 (isoleucine or threonine), aa42 (valine or alanine) and aa238 (asparagine or aspartic acid/serine) and NSP4 at aa135 (isoleucine or valine). No amino acid changes were identified in gene 6. The observed amino acid differences occurred in proteins that have been implicated in virulence, and correlate with differences in clinical symptoms of infants infected with these strains. These results permit speculation about the genetic basis for virulence of human strains.

Serological response to rotavirus infection in newborn infants

We report the identification of rotavirus in stools of newborn infants at the "Hospital Materno Infantil de Caricuao" (HMIC) as well as the infants' serological responses to various rotavirus strains. The serological responses of another group of rotavirus-positive neonates studied previously at the "Maternidad Concepcion Palacios" (MCP) hospital was also evaluated. Fifty-four of 266 (20%) newborns examined at HMIC shed rotavirus. The infection rate was higher among infants admitted to the nursery (75%) than in those "rooming in" with their mothers (7%) (P < .01). Eleven of the 54 neonates (20%) had diarrhea; seven of them experienced mild, short-lived episodes, whereas five had frequent diarrhea bouts or diarrhea lasting for over 3 days; the remaining 43 infants were asymptomatic. Twenty-seven of 28 rotavirus specimens tested at HMIC had VP7 serotype 4 specificity and one belonged to VP7 serotype 1; VP4 typing performed on 24 of the viruses by RNA hybridization showed these viruses to be similar to the M37 strain, a rotavirus previously associated with asymptomatic infections in newborns at MCP. IgA seroresponses were detected in eight of 11 infants born at HMIC (73%), but most failed to developed neutralization responses to homologous or heterologous strains. Newborn infants who had shed the M37 rotavirus strain at MCP reacted similarly: 16 of 24 (67%) developed a rotavirus IgA rise, but only 29% developed a neutralization response.

Sequence conservation within neutralization epitope regions of VP7 and VP4 proteins of human serotype G4 rotavirus isolates

Serotype G4 rotavirus isolates causing four separate epidemics of severe diarrhoea in young children in Melbourne, Australia (from 1974-1990) were investigated for sequence variation in genes encoding the outer capsid proteins, VP4 and VP7. Complementary DNA of the gene encoding the major outer capsid neutralization antigen, VP7, of eighteen isolates was synthesized and amplified by coupled reverse transcription and polymerase chain reaction. Direct sequencing methods were used to derive the deduced amino acid sequences of the immunodominant A, B, and C neutralization epitope regions of the protein. Limited variation was observed among all isolates. A threonine to asparagine change in region A, at amino acid 96, was associated with altered binding of serotype G4-specific neutralizing monoclonal antibodies. The VP8* region of the outer capsid protein VP4 (containing the proposed serotype-specific neutralization epitopes) was investigated in eight isolates. This region was found to highly conserved both within Melbourne isolates and in relation to the standard strains Wa, P, and VA70. The characteristic periodicity of occurrence of serotype G4 isolates causing severe diarrhoea in Melbourne children is unlikely to be due to changes in neutralization epitopes located on the outer capsid proteins, VP7 or VP4.

Intra- and inter-season genetic variability in the VP7 gene of serotype 1 (monotype 1 a) rotavirus clinical isolates

Nucleotide sequence variation was detected in the VP7 gene of serotype 1 (monotype 1 a) rotavirus isolates collected from children admitted to hospital in Melbourne with acute diarrhoea in 1990 and 1991. Two co-circulating electropherotypes were detected during the 1991 winter epidemic. Using chemical cleavage of mismatches in heteroduplexes, the genes encoding VP7 were found to be genetically stable within each electropherotype during the study period, although differences between the two types were apparent. Direct nucleotide sequencing confirmed this finding. The two electropherotypes exhibited four nucleotide differences in the VP7 gene, only one of which resulted in a substitution in the deduced amino acid sequence. The degree of variation was more pronounced between the 1991 isolates and those from the previous winter, with approximately 3% nucleotide sequence diversity between isolates from both winters. The regions encoding the neutralization epitopes of VP7 were conserved among all isolates. Comparison to the local prototype monotype 1 a strain, RV 4 (isolated from a child admitted to hospital in Melbourne in 1981), implies that the 1990 and 1991 isolates have diverged independently. This suggests that genetically distinct strains emerge from a pool of related viruses to predominate in any given year.

Further characterisation of human rotaviruses isolated from asymptomatically infected neonates in South Africa

Stool specimens were collected from healthy neonates at Ga-Rankuwa Hospital in the winters of 1984 and 1986 and tested for the presence of rotavirus infection. Asymptomatic excretion was found to occur in 25% of the newborn babies analysed. Gel electrophoresis of the rotavirus RNA genome revealed that a genomically stable strain of rotavirus was endemic in the ward at the time intervals examined. Hybridisation analysis of the VP4 and VP7 rotavirus genes, which encode the outer capsid neutralization proteins of the virus, was conducted. These results showed the presence of a serotype 4 rotavirus strain with an M37-like VP4 gene allele, which remained conserved in the nursery over the time period examined. Partial nucleotide sequences were obtained for a variable region of the VP7 gene and for the hyperdivergent region of the VP4 gene from 8 of these viruses and showed that remarkable conservation of these regions in the genes of the viruses occurred over time.

Rotavirus detection by dot blot hybridization assay using a non-radioactive synthetic oligodeoxynucleotide probe

A synthetic oligodeoxynucleotide of 40 nucleotides corresponding to nucleotides 33-72 of the gene coding for the viral protein VP7 of rotavirus, was used as a nucleic acid probe to develop a non-radioactive hybridization method for rotavirus detection. The probe was labelled at the 3' end with biotin-7-dATP. The sensitivity and specificity of the dot blot hybridization assay for rotavirus detection was evaluated with 303 stool specimens. The results indicate that the hybridization assay has a higher sensitivity than both PAGE and EIA. Among the rotavirus strains tested 37 different electropherotypes were found. The results suggest that rotavirus diagnosis by dot hybridization using a non-radioactive probe may become routine laboratory procedure because it is simple, highly specific and very sensitive.

Molecular evidence for naturally occurring single VP7 gene substitution reassortant between human rotaviruses belonging to two different genogroups

Twenty four stool rotaviruses that comprised 22 distinct electropherotypes were selected for genome analysis from the collection of diarrheal specimens obtained over an eight-year period. These 22 electropherotypes were found in 46% of the total electropherotypes identified during the previous studies and represented 328 (64%) of rotavirus specimens in the collection. When genomic RNAs from these stool rotaviruses were hybridized to the 32P-labeled transcription probes prepared from prototypes representing three human rotavirus genogroups, Wa, DS-1, and AU-1, any one of the isolates showed a high degree of homology only with one of the three probes, which data confirmed and extended our previous observation on the existence of three distinct genogroups among human rotaviruses. Two stool rotaviruses which had an unusual combination of serotype (G1), subgroup (I) and RNA pattern (an identical short electropherotype), however, yielded the hybridization pattern indicative of an intergenogroupic single VP7 gene substitution reassortant. When they were cell culture adapted and analyzed by RNA-RNA hybridization, molecular evidence was obtained indicating that their VP7 gene derived from viruses belonging to the Wa genogroup whereas the remaining 10 genes hybridized with viruses belonging to the DS-1 genogroup. Interestingly, these natural reassortants emerged in the midst of the rotavirus season in which G1 strains predominated.

Characterization of rotavirus electropherotypes excreted by symptomatic and asymptomatic infants

Human rotavirus isolates from 1100 stool samples were analyzed by polyacrylamide gel electrophoresis, and 48 different migration patterns were detected. Heterogeneity in the migration of segment 10 was observed in both long and short electropherotypes in which three long and two short patterns were identified. In spite of these variations all short and long electropherotypes were subgrouped by enzyme immunoassay as subgroups I and II respectively. Mixed infections were detected in 17% of cases and the subgrouping correlated with the corresponding electropherotypes. The same electropherotypes were present in severe, mild and asymptomatic cases and no electropherotype was particularly associated with greater virulence. Furthermore, the electropherotypes isolated from nosocomial asymptomatic cases were the same as those detected from those admitted with severe diarrhea. It seems unlikely that electropherotyping can be used to identify more virulent strains of rotavirus.

Comparison of reactogenicity and antigenicity of M37 rotavirus vaccine and rhesus-rotavirus-based quadrivalent vaccine

90 Venezuelan infants aged 10-20 weeks were randomly allocated to four groups which received one of the following: the M37 vaccine (1 x 10(4) pfu [plaque-forming units]); quadrivalent rotavirus vaccine (1 x 10(4) pfu each of serotype 3 rhesus rotavirus [RRV] and human rotavirus-RRV reassortants of serotypes 1, 2, and 4); balanced quadrivalent vaccine consisting of 1 x 10(4) pfu of serotype 1 and 3 components but 5 x 10(4) pfu of serotype 2 and 4 components; or placebo. The frequencies of transient febrile responses in these four groups were 20%, 27%, 30%, and 9%. 50% of 22 infants tested who received M37 vaccine showed a serum rotavirus IgA antibody response, compared with 74% of the 23 quadrivalent and 86% of the 22 balanced-quadrivalent recipients. 64% of the M37 recipients showed a neutralising antibody response to M37; 27% showed such responses to human serotype 1 Wa strain and 27% to serotype 4 neonatal strain ST3. 17-39% of the quadrivalent recipients and 27-41% of the balanced-quadrivalent recipients showed neutralising antibody responses to serotypes 1-4. 70-73% of the quadrivalent and balanced quadrivalent groups also showed neutralising antibody responses to RRV.