Analysis of Archival Sera from Norovirus-Infected Individuals Demonstrates that Cross-Blocking of Emerging Viruses is Genotype-Specific

BACKGROUND

Rapidly evolving RNA viruses, such as human norovirus, generate extraordinary sequence diversity, posing a significant challenge to vaccine design. This diversity coupled with short-lasting natural immunity leads to re-infection throughout one's lifetime. How re-exposure shapes humoral immunity to future norovirus strains remains incompletely understood.

METHODS

We profiled the antibody responses following two community gastroenteritis outbreaks with GII.2 and GII.6 noroviruses in 1971. Using diverse VLPs, ELISA, and carbohydrate-blocking assays (surrogate for neutralization), we examined the antibody response at acute and convalescent timepoints following GII.6 infection.

RESULTS

Convalescent sera displayed strong homologous blocking, demonstrating a 5-fold increase in GII.6 carbohydrate-blockade over acute samples, and broad blocking of diverse archival and modern GII.6 noroviruses. Convalescent sera displayed limited carbohydrate-blocking of heterotypic VLPs, despite high ELISA binding titers. Select individuals developed broad cross-genotype blockade, but this response was established before the second outbreak. Finally, we applied a novel competitive carbohydrate-blocking assay to demonstrate the epitope-specificity and discrete compartments of the neutralizing response.

CONCLUSIONS

Our data show that infection generates narrow, focused immunity directed towards the infecting genotype. We did detect broad cross-blocking in specific individuals, but these responses could be attributed to diverse, genotype-specific antibodies pre-dating GII.6 infection.

Norovirus evolves as one or more distinct clonal populations in immunocompromised hosts

Noroviruses are a major cause of acute gastroenteritis worldwide and can establish chronic infection in immunocompromised individuals. To investigate the mechanisms of norovirus evolution during chronic infection, we selected seven representative patients from a National Institutes of Health study cohort who sustained norovirus infection for periods ranging from 73 to 1,492 days. Six patients shed viruses belonging to a single genotype (GII.2[PNA], GII.4 New Orleans[P4], GII.4 Den Haag[P4], GII.3[P21], GII.6[P7], or GII.14[P7]) over the period examined, while one patient sequentially shed two genotypes (GII.6[P7] followed by GII.4 Sydney[P31]). Norovirus genomes from consecutive stool samples were sequenced at high resolution (>3,300 reads/nucleotide position) using the Illumina platform and subjected to bioinformatics analysis. Norovirus sequences could be resolved into one or more discrete clonal RNA genomes that persisted within these patients over time. Phylogenetic analyses inferred that clonal populations originated from a single founder virus and not by reinfection with community strains. Estimated evolutionary rates of clonal populations during persistent infection were similar to those of noroviruses from acute infection in the global database, suggesting that inherently higher RNA-dependent polymerase error rates were not associated with the ability to persist. The high-resolution analysis of norovirus diversity and evolution at the population level described here should allow a better understanding of adaptive mutations sustained during chronic infection. IMPORTANCE Noroviruses are an important cause of chronic diarrhea in patients with compromised immune systems. Presently, there are no effective therapies to clear the virus, which can persist for years in the intestinal tract. The goal of our study was to develop a better understanding of the norovirus strains that are associated with these long-term infections. With the remarkable diversity of norovirus strains detected in the immunocompromised patient cohort we studied, it appears that most, if not all, noroviruses circulating in nature may have the capacity to establish a chronic infection when a person is unable to mount an effective immune response. Our work is the most comprehensive genetic data set generated to date in which near full-length genomes from noroviruses associated with chronic infection were analyzed by high-resolution next-generation sequencing. Analysis of this data set led to our discovery that certain patients in our cohort were shedding noroviruses that could be subdivided into distinct haplotypes or populations of viruses that were co-evolving independently. The ability to track haplotypes of noroviruses during chronic infection will allow us to fine-tune our understanding of how the virus adapts and maintains itself in the human host, and how selective pressures such as antiviral drugs can affect these distinct populations.

Cross-reactive neutralizing human monoclonal antibodies mapping to variable antigenic sites on the norovirus major capsid protein

Human noroviruses are the major viral cause of acute gastroenteritis around the world. Although norovirus symptoms are in most cases mild and self-limited, severe and prolonged symptoms can occur in the elderly and in immunocompromised individuals. Thus, there is a great need for the development of specific therapeutics that can help mitigate infection. In this study, we sought to characterize a panel of human monoclonal antibodies (mAbs; NORO-123, -115, -273A, -263, -315B, and -250B) that showed carbohydrate blocking activity against the current pandemic variant, GII.4 Sydney 2012. All antibodies tested showed potent neutralization against GII.4 Sydney virus in human intestinal enteroid culture. While all mAbs recognized only GII.4 viruses, they exhibited differential binding patterns against a panel of virus-like particles (VLPs) representing major and minor GII.4 variants spanning twenty-five years. Using mutant VLPs, we mapped five of the mAbs to variable antigenic sites A (NORO-123, -263, -315B, and -250B) or C (NORO-115) on the major capsid protein. Those mapping to the antigenic site A showed blocking activity against multiple variants dating back to 1987, with one mAb (NORO-123) showing reactivity to all variants tested. NORO-115, which maps to antigenic site C, showed reactivity against multiple variants due to the low susceptibility for mutations presented by naturally-occurring variants at the proposed binding site. Notably, we show that cross-blocking and neutralizing antibodies can be elicited against variable antigenic sites. These data provide new insights into norovirus immunity and suggest potential for the development of cross-protective vaccines and therapeutics.

Global and regional circulation trends of norovirus genotypes and recombinants, 1995-2019: A comprehensive review of sequences from public databases

Human noroviruses are the leading global cause of viral gastroenteritis. Attempts at developing effective vaccines and treatments against norovirus disease have been stymied by the extreme genetic diversity and rapid geographic distribution of these viruses. The emergence and replacement of predominantly circulating norovirus genotypes has primarily been attributed to mutations on the VP1 capsid protein leading to genetic drift, and more recently to recombination events between the ORF1/ORF2 junction. However, large‐scale research into the historical and geographic distribution of recombinant norovirus strains has been limited in the literature. We performed a comprehensive historical analysis on 30,810 human norovirus sequences submitted to public databases between the years 1995 and 2019. During this time, 37 capsid genotypes and 56 polymerase types were detected across 90 different countries, and 97 unique recombinant genomes were also identified. GII.4, both capsid and polymerase, was the predominately circulating type worldwide for the majority of this time span, save for a brief swell of GII.17 and GII.2 capsid genotypes and a near‐total eclipse by GII.P16, GII.P21 and GII.P31 beginning in 2013. Interestingly, an analysis of 4067 recombinants found that 50.2% (N = 2039) of all recorded sequences belonged to three recently emerged recombinant strains: GII.2[P16], GII.4[P31], and GII.4[P16]. This analysis should provide an important historical foundation for future studies that evaluate the emergence and distribution of noroviruses, as well as the design of cross‐protective vaccines.

Dynamic immunodominance hierarchy of neutralizing antibody responses to evolving GII.4 noroviruses

A paradigm of RNA viruses is their ability to mutate and escape from herd immunity. Because antibody responses are a major effector for viral immunity, antigenic sites are usually under strong diversifying pressure. Here, we use norovirus as a model to study mechanisms of antigenic diversification of non-enveloped, fast-evolving RNA viruses. We comprehensively characterize all variable antigenic sites involved in virus neutralization and find that single neutralizing monoclonal antibodies (mAbs) map to multiple antigenic sites of GII.4 norovirus. Interactions of multiple epitopes on the viral capsid surface provide a broad mAb-binding repertoire with a remarkable difference in the mAb-binding profiles and immunodominance hierarchy for two distantly related GII.4 variants. Time-ordered mutant viruses confirm a progressive change of antibody immunodominance along with point mutations during the process of norovirus evolution. Thus, in addition to point mutations, switches in immunodominance that redirect immune responses could facilitate immune escape in RNA viruses.

Understanding the relationship between norovirus diversity and immunity

Human noroviruses are the most common viral cause of acute gastroenteritis worldwide. Currently, there are no approved vaccines or specific therapeutics to treat the disease. Some obstacles delaying the development of a norovirus vaccine are: (i) the extreme diversity presented by noroviruses; (ii) our incomplete understanding of immunity to noroviruses; and (iii) the lack of a robust cell culture system or animal model for human noroviruses. Recent advances in in vitro cultivation of norovirus, novel approaches applied to viral genomics and immunity, and completion of vaccine trials and birth cohort studies have provided new information toward a better understanding of norovirus immunity. Here, we will discuss the complex relationship between norovirus diversity and correlates of protection for human noroviruses, and how this information could be used to guide the development of cross-protective vaccines.

Viral intra-host evolution in immunocompetent children contributes to human norovirus diversification at the global scale

Norovirus is a major cause of acute gastroenteritis. Human noroviruses present >30 different genotypes, with a single genotype (GII.4) predominating worldwide. Concurrent outbreaks of norovirus are often associated with the emergence of new viruses. While different hypotheses have been presented, the source of new mutations in noroviruses is still unknown. In this study, we applied high-resolution sequencing to determine the intra-host viral diversity presented by noroviruses during the acute and shedding phase of infection in children. Profiling viral intra-host diversification at nearly full genome level indicated that GII.4 viruses presented dynamic intra-host variation, while non-GII.4 viruses presented minimal variation throughout the infection. Notably, the intra-host genetic variation during the shedding phase recapitulates the genetic diversity observed at the global level, particularly those mapping at the VP1 antigenic sites. Thus the intra-host evolution in healthy children explains the source of norovirus mutations that results in diversification at the global scale.

Genome-wide analyses of human noroviruses provide insights on evolutionary dynamics and evidence of coexisting viral populations evolving under recombination constraints

Norovirus is a major cause of acute gastroenteritis worldwide. Over 30 different genotypes, mostly from genogroup I (GI) and II (GII), have been shown to infect humans. Despite three decades of genome sequencing, our understanding of the role of genomic diversification across continents and time is incomplete. To close the spatiotemporal gap of genomic information of human noroviruses, we conducted a large-scale genome-wide analyses that included the nearly full-length sequencing of 281 archival viruses circulating since the 1970s in over 10 countries from four continents, with a major emphasis on norovirus genotypes that are currently underrepresented in public genome databases. We provided new genome information for 24 distinct genotypes, including the oldest genome information from 12 norovirus genotypes. Analyses of this new genomic information, together with those publicly available, showed that (i) noroviruses evolve at similar rates across genomic regions and genotypes; (ii) emerging viruses evolved from transiently-circulating intermediate viruses; (iii) diversifying selection on the VP1 protein was recorded in genotypes with multiple variants; (iv) non-structural proteins showed a similar branching on their phylogenetic trees; and (v) contrary to the current understanding, there are restrictions on the ability to recombine different genomic regions, which results in co-circulating populations of viruses evolving independently in human communities. This study provides a comprehensive genetic analysis of diverse norovirus genotypes and the role of non-structural proteins on viral diversification, shedding new light on the mechanisms of norovirus evolution and transmission.

Norovirus is a highly diverse enteric pathogen. The large genomic database accumulated in the last three decades advanced our understanding of norovirus diversity; however, this information is limited by geographical bias, sporadic times of collection, and missing or incomplete genome sequences. In this multinational collaborative study, we mined archival samples collected since the 1970s and sequenced nearly full-length new genomes from 281 historical noroviruses, including the first full-length genomic sequences for three genotypes. Using this novel dataset, we found evidence for restrictions in the recombination of genetically disparate viruses and that diversifying selection results in new variants with different epidemiological profiles. These new insights on the diversification of noroviruses could provide baseline information for the study of future epidemics and ultimately the prevention of norovirus infections.

Recombinant Nontypeable Genotype II Human Noroviruses in the Americas

We report multiple nontypeable genotype II noroviruses circulating in South America; nucleotides differed by >25% from those of other genotypes. These viruses have been circulating in the Americas for ≈20 years and show recombination with other genotypes. Clues to norovirus natural history can guide development of treatment and prevention plans.

Norovirus-specific immunoglobulin A in breast milk for protection against norovirus-associated diarrhea among infants

BACKGROUND

Norovirus (NV) causes acute gastroenteritis in infants. Humoral and fecal immunoglobulin A (IgA) responses have been correlated with protection against NV; however, the role of breast milk IgA against NV infection and associated diarrhea is still unknown. This study aimed to evaluate the protective role of NV-specific IgA (NV-IgA) in breast milk.

METHODS

Ninety-five breast milk samples collected from mothers enrolled in a 2016-2017 Peruvian birth cohort study were tested for total IgA and NV-IgA by ELISA using GII·4 variants and non-GII·4 genotype virus-like particles (VLPs). Breast milk samples were grouped according to the NV infection and diarrheal status of infants: NV positive with diarrhea (NV+D+, n=18); NV positive without diarrhea (NV+D-, n=37); and NV negative without diarrhea (NV-D-, n=40). The percent positivity and titer of NV-IgA were compared among groups. The cross-reactivity was estimated based on the correlation of ratio between NV-IgA against GII·4 variants and non-GII·4 genotype VLPs.

FINDINGS

NV-IgA had high positivity rates against different VLPs, especially against GII (89-100%). The NV+D- group had higher percent positivity (89% vs. 61%, p=0·03) and median titer (1:100 vs 1:50, p=0·03) of NV-IgA than the NV+D+ group against GI·1 VLPs. A relatively high correlation between different GII·4 variants (0·87) and low correlation between genogroups (0·23-0·37) were observed.

INTERPRETATION

Mothers with high positivity rates and titers of NV-IgA in breast milk had NV infected infants with reduced diarrheal symptoms. Antigenic relatedness to the genetic diversity of human norovirus was suggested.Funding National Institute of Allergy and Infectious Diseases, National Institute of Health: 1R01AI108695-01A1 and the Japan Society for the Promotion of Science (Fostering Joint International Research B):19KK0241.

Neutralizing Antibody Responses to Homologous and Heterologous H1 and H3 Influenza A Strains After Vaccination With Inactivated Trivalent Influenza Vaccine Vary With Age and Prior-year Vaccination

BACKGROUND

Prior influenza immunity influences the homologous neutralizing antibody responses elicited by inactivated influenza vaccines (IIV), but neutralizing antibody responses to heterologous strains have not been extensively characterized.

METHODS

We analyzed neutralizing antibody titers in individuals aged 1-88 who received the 2009-2010 season IIV before infection by or vaccination against the 2009 pandemic H1N1 virus. Neutralization titers to homologous and heterologous past, recent, and advanced H1 and H3 strains, as well as H2, H5, and H7 strains, were measured using influenza hemagglutinin pseudoviruses. We performed exploratory analyses based on age, prior-year IIV, and prevaccination titer, without controlling for Type I errors.

RESULTS

IIV elicited neutralizing antibodies to past and advanced H1 and H3 strains, as well as to an H2 strain in individuals who were likely infected early in life. The neutralization of avian subtype viruses was rare, and there was no imprinting of neutralization responses to novel avian subtype viruses based on the influenza group. Compared to adults, children had higher seroresponse rates to homologous and heterologous strains, and their sera generated larger antigenic distances among strains. Seroresponse rates to homologous and heterologous strains were lower in subjects vaccinated with prior-year IIV, though postimmunization titers were generally high.

CONCLUSIONS

IIV elicited neutralizing antibodies to heterologous H1 and H3 strains in all ages groups, but titers and seroresponse rates were usually higher in children. Prior-year vaccination with the same strains tended to blunt IIV neutralization responses to all strains in young and old age groups, yet postimmunization titers were high.

Updated classification of norovirus genogroups and genotypes

Noroviruses are genetically diverse RNA viruses associated with acute gastroenteritis in mammalian hosts. Phylogenetically, they can be segregated into different genogroups as well as P (polymerase)-groups and further into genotypes and P-types based on amino acid diversity of the complete VP1 gene and nucleotide diversity of the RNA-dependent RNA polymerase (RdRp) region of ORF1, respectively. In recent years, several new noroviruses have been reported that warrant an update of the existing classification scheme. Using previously described 2× standard deviation (sd) criteria to group sequences into separate clusters, we expanded the number of genogroups to 10 (GI-GX) and the number of genotypes to 48 (9 GI, 27 GII, 3 GIII, 2 GIV, 2 GV, 2 GVI and 1 genotype each for GVII, GVIII, GIX [formerly GII.15] and GX). Viruses for which currently only one sequence is available in public databases were classified into tentative new genogroups (GNA1 and GNA2) and genotypes (GII.NA1, GII.NA2 and GIV.NA1) with their definitive assignment awaiting additional related sequences. Based on nucleotide diversity in the RdRp region, noroviruses can be divided into 60 P-types (14 GI, 37 GII, 2 GIII, 1 GIV, 2 GV, 2 GVI, 1 GVII and 1 GX), 2 tentative P-groups and 14 tentative P-types. Future classification and nomenclature updates will be based on complete genome sequences and will be coordinated and disseminated by the international norovirus classification-working group.

Genotype-Specific Neutralization of Norovirus Is Mediated by Antibodies Against the Protruding Domain of the Major Capsid Protein

Human noroviruses are the most common viral agents of acute gastroenteritis. Recently, human intestinal enteroids were shown to be permissive for norovirus infection. We tested their suitability as a system to study norovirus neutralization. Hyperimmune sera raised against virus-like particles (VLPs) representing different genotypes showed highly specific neutralization activity against GII.4 and GII.6 noroviruses. Carbohydrate blocking assays and neutralization exhibited similar patterns in antibody responses. Notably, sera produced against chimeric VLPs that presented swapped structural shell and protruding (P) domains, from different genotypes showed that neutralization is primarily mediated by antibodies mapping to the P domain of the norovirus capsid protein. This study provides empirical information on the antigenic differences among genotypes as measured by neutralization, which could guide vaccine design.

Emergence of norovirus strains: A tale of two genes

Noroviruses are a very diverse group of viruses that infect different mammalian species. In humans, norovirus is a major cause of acute gastroenteritis. Multiple norovirus infections can occur in a lifetime as the result of limited duration of acquired immunity and cross-protection among different strains. A combination of advances in sequencing methods and improvements on surveillance has provided new insights into norovirus diversification and emergence. The generation of diverse norovirus strains has been associated with (1) point mutations on two different genes: ORF1, encoding the non-structural proteins, and ORF2, encoding the major capsid protein (VP1); and (2) recombination events that create chimeric viruses. While both mechanisms are exploited by all norovirus strains, individual genotypes utilize each mechanism differently to emerge and persist in the human population. GII.4 noroviruses (the most prevalent genotype in humans) present an accumulation of amino acid mutations on VP1 resulting in the chronological emergence of new variants. In contrast, non-GII.4 noroviruses present co-circulation of different variants over long periods with limited changes on their VP1. Notably, genetic diversity of non-GII.4 noroviruses is mostly related to the high number of recombinant strains detected in humans. While it is difficult to determine the precise mechanism of emergence of epidemic noroviruses, observations point to multiple factors that include host-virus interactions and changes on two regions of the genome (ORF1 and ORF2). Larger datasets of viral genomes are needed to facilitate comparison of epidemic strains and those circulating at low levels in the population. This will provide a better understanding of the mechanism of norovirus emergence and persistence.

Sequential Gastroenteritis Outbreaks in a Single Year Caused by Norovirus Genotypes GII.2 and GII.6 in an Institutional Setting

Background

Norovirus is a leading cause of acute gastroenteritis worldwide. Improved diagnostic capability has been instrumental in the characterization of archival norovirus strains associated with gastroenteritis outbreaks that were investigated decades ago. One such investigation was that of 2 sequential gastroenteritis outbreaks that occurred in 1971 at the former Henryton State Hospital in Maryland. Approximately 40% of the resident population experienced clinical symptoms in both outbreaks, which occurred 11 months apart.

Methods

Stored stools and paired sera were re-analyzed to investigate the etiology of the 2 outbreaks.

Results

Different norovirus genotypes were identified as the etiological agents responsible for the illnesses, with GII.2 associated with the first outbreak and GII.6 with the second. The viruses were antigenically distinct as determined by analyses of hyperimmune sera raised against the corresponding virus-like particles in animals, as well as paired sera from infected individuals.

Conclusions

The observed antigenic differences were consistent with the failure of the GII.2 strain to provide cross-protective immunity to the GII.6 strain a few months later. An understanding of antigenic diversity among norovirus genotypes will be important in the design of norovirus vaccines.

A Luciferase Immunoprecipitation System (LIPS) assay for profiling human norovirus antibodies

A luciferase immunoprecipitation systems (LIPS) assay was developed to define the antigenic specificity and titer of antibodies directed against human norovirus (HuNoV). Recombinant proteins, expressed by plasmid constructs encoding Renilla luciferase (Ruc) fused to the full-length HuNoV major capsid protein (VP1) (Ruc-antigen), were generated for ten HuNoV strains. In addition, subdomain constructs Ruc-Shell (S) and Ruc-Protruding (P) were engineered for a representative GII.4 norovirus (strain GII.4/2006b). The LIPS assay measured antibody levels in a well-defined panel of HuNoV-specific sera, and the results were compared to an ELISA standard. In hyperimmune sera, the LIPS produced titers similar to or higher than those measured by the ELISA of HuNoV-specific antibodies. The specificity of antibodies in various sera was profiled by LIPS with a panel of diverse Ruc-antigens containing full-length HuNoV VP1 proteins or VP1 subdomains, and the assay detected both specific and cross-reactive antibodies. Competition assays, in which antibodies were pre-incubated with one or more intact VLPs representing different genotypes, proved useful in further assessment of the antibody specificity detected by LIPS in complex polyclonal sera. The profiling of HuNoV-specific antibodies in the high-throughput LIPS format may prove useful in defining the strength or specificity of the adaptive immune response following natural infection or vaccination.

Static and Evolving Norovirus Genotypes: Implications for Epidemiology and Immunity

Noroviruses are major pathogens associated with acute gastroenteritis worldwide. Their RNA genomes are diverse, with two major genogroups (GI and GII) comprised of at least 28 genotypes associated with human disease. To elucidate mechanisms underlying norovirus diversity and evolution, we used a large-scale genomics approach to analyze human norovirus sequences. Comparison of over 2000 nearly full-length ORF2 sequences representing most of the known GI and GII genotypes infecting humans showed a limited number (≤5) of distinct intra-genotypic variants within each genotype, with the exception of GII.4. The non-GII.4 genotypes were comprised of one or more intra-genotypic variants, with each variant containing strains that differed by only a few residues over several decades (remaining "static") and that have co-circulated with no clear epidemiologic pattern. In contrast, the GII.4 genotype presented the largest number of variants (>10) that have evolved over time with a clear pattern of periodic variant replacement. To expand our understanding of these two patterns of diversification ("static" versus "evolving"), we analyzed using NGS the nearly full-length norovirus genome in healthy individuals infected with GII.4, GII.6 or GII.17 viruses in different outbreak settings. The GII.4 viruses accumulated mutations rapidly within and between hosts, while the GII.6 and GII.17 viruses remained relatively stable, consistent with their diversification patterns. Further analysis of genetic relationships and natural history patterns identified groupings of certain genotypes into larger related clusters designated here as "immunotypes". We propose that "immunotypes" and their evolutionary patterns influence the prevalence of a particular norovirus genotype in the human population.

Detection of novel GII.17 norovirus in Argentina, 2015

During the winter of 2014-2015 a novel GII.17 norovirus strain emerged as a cause of large gastroenteritis outbreaks in Asia; displacing the long-term predominant strain, GII.4. Although sporadically detected, the emerging GII.17 virus was described in North America and Europe. In this study, we describe the presence of this novel strain in Argentina (South America), and provide new information on the genetic diversity of GII.17 noroviruses. Ten stool samples from individuals (1-88years old; median: 5years old) experiencing gastroenteritis symptoms from San Martín de los Andes, Argentina were tested for Norovirus using RT-PCR. Subsequently, Norovirus positive samples were analyzed by sequencing. Norovirus was found in four out of 10 samples received. Partial sequencing of the ORF2 was available for 3/4 samples: two samples belonged to genotype GII.4 and one to genotype GII.17 (Arg13099). Sequence analyses of the VP1 encoding region revealed that the GII.17 Argentinean strain presented characteristics from both, the new (cluster C), and older (cluster A and B) GII.17 strains. Phylogenetic and sequence analyses of the RdRp region showed that this strain was closely related to strains from genotypes GII.P3, GII.P13 and GII.P17; however, did not cluster within any of them. This study represents the first report of this emergent strain in South America, and presents further evidence of the genetic plasticity of the GII.17.

Epidemiology of Norovirus Infection Among Immunocompromised Patients at a Tertiary Care Research Hospital, 2010-2013

Background. Noroviruses are a major cause of infectious gastroenteritis worldwide, and viruses can establish persistent infection in immunocompromised individuals. Risk factors and transmission in this population are not fully understood.

Methods. From 2010 through 2013, we conducted a retrospective review among immunocompromised patients (n = 268) enrolled in research studies at the National Institutes of Health Clinical Center and identified a subset of norovirus-positive patients (n = 18) who provided stool specimens for norovirus genotyping analysis.

Results. Norovirus genome was identified by reverse-transcription quantitative polymerase chain reaction in stools of 35 (13%) of the 268 immunocompromised patients tested, and infection prevalence was 21% (11 of 53) in persons with primary immune deficiencies and 12% (20 of 166) among persons with solid tumors or hematologic malignancies. Among 18 patients with norovirus genotyping information, norovirus GII.4 was the most prevalent genotype (14 of 18, 78%). Persistent norovirus infection (≥6 months) was documented in 8 of 18 (44%) individuals. Phylogenetic analysis of the GII.4 capsid protein sequences identified at least 5 now-displaced GII.4 variant lineages, with no evidence of their nosocomial transmission in the Clinical Center.

Conclusions. Norovirus was a leading enteric pathogen identified in this immunocompromised population. Both acute and chronic norovirus infections were observed, and these were likely community-acquired. Continued investigation will further define the role of noroviruses in these patients and inform efforts toward prevention and treatment.

Mapping and modeling of a strain-specific epitope in the Norwalk virus capsid inner shell

Noroviruses are diverse positive-strand RNA viruses associated with acute gastroenteritis. Cross-reactive epitopes have been mapped primarily to conserved sequences in the capsid VP1 Shell (S) domain, and strain-specific epitopes to the highly variable Protruding (P) domain. In this work, we investigated a strain-specific linear epitope defined by MAb NV10 that was raised against prototype (Genogroup I.1) strain Norwalk virus (NV). Using peptide scanning and mutagenesis, the epitope was mapped to amino acids 21-32 (LVPEVNASDPLA) of the NV S domain, and its specificity was verified by epitope transfer and reactivity with a recombinant MAb NV10 single-chain variable fragment (scFv). Comparative structural modeling of the NV10 strain-specific and the broadly cross-reactive TV20 epitopes identified two internal non-overlapping sites in the NV shell, corresponding to variable and conserved amino acid sequences among strains, respectively. The S domain, like the P domain, contains strain-specific epitopes that contribute to the antigenic diversity among the noroviruses.

Genome of Emerging Norovirus GII.17, United States, 2014

To determine whether the norovirus strain GII.17 recently detected in Maryland, USA, (Hu/GII.17/Gaithersburg/2014/US) is spreading globally, we characterized the genome. High similarity with the norovirus GII.17 that caused recent outbreaks in Asia indicates that the same strain was present in the United States during the 2014–15 norovirus season (winter).

Genetic linkage of capsid protein-encoding RNA segments in group A equine rotaviruses

Rotavirus virions are formed by three concentric protein layers that enclose the 11 dsRNA genome segments and the viral proteins VP1 and VP3. Interactions amongst the capsid proteins (VP2, VP6, VP7 and VP4) have been described to play a major role in viral fitness, whilst restricting the reassortment of the genomic segments during co-infection with different rotavirus strains. In this work we describe and characterize the linkage between VP6 and VP7 proteins based on structural and genomic analyses of group A rotavirus strains circulating in Argentinean horses. Strains with the VP7 genotype G3 showed a strong association with the VP6 genotype I6, whilst strains with G14 were associated with the I2 genotype. Most of the differences on the VP6 and VP7 proteins were observed in interactive regions between the two proteins, suggesting that VP6 : VP7 interactions may drive the co-evolution and co-segregation of their respective gene segments.

Llama nanoantibodies with therapeutic potential against human norovirus diarrhea

Noroviruses are a major cause of acute gastroenteritis, but no vaccines or therapeutic drugs are available. Llama-derived single chain antibody fragments (also called VHH) are small, recombinant monoclonal antibodies of 15 kDa with several advantages over conventional antibodies. The aim of this study was to generate recombinant monoclonal VHH specific for the two major norovirus (NoV) genogroups (GI and GII) in order to investigate their potential as immunotherapy for the treatment of NoV diarrhea. To accomplish this objective, two llamas were immunized with either GI.1 (Norwalk-1968) or GII.4 (MD2004) VLPs. After immunization, peripheral blood lymphocytes were collected and used to generate two VHH libraries. Using phage display technology, 10 VHH clones specific for GI.1, and 8 specific for GII.4 were selected for further characterization. All VHH recognized conformational epitopes in the P domain of the immunizing VP1 capsid protein, with the exception of one GII.4 VHH that recognized a linear P domain epitope. The GI.1 VHHs were highly specific for the immunizing GI.1 genotype, with only one VHH cross-reacting with GI.3 genotype. The GII.4 VHHs reacted with the immunizing GII.4 strain and showed a varying reactivity profile among different GII genotypes. One VHH specific for GI.1 and three specific for GII.4 could block the binding of homologous VLPs to synthetic HBGA carbohydrates, saliva, and pig gastric mucin, and in addition, could inhibit the hemagglutination of red blood cells by homologous VLPs. The ability of Nov-specific VHHs to perform well in these surrogate neutralization assays supports their further development as immunotherapy for NoV treatment and immunoprophylaxis.

Sequential gastroenteritis episodes caused by 2 norovirus genotypes

We investigated sequential episodes of acute norovirus gastroenteritis in a young child within an 11-month period. The infections were caused by 2 distinct genotypes (GII.4 and GII.6). Failure to achieve cross-protective immunity was linked to absence of an enduring and cross-reactive mucosal immune response, a critical consideration for vaccine design.

Genomic characterization of a rotavirus G8P[1] detected in a child with diarrhea reveal direct animal-to-human transmission

Group A rotavirus is a major cause of severe gastroenteritis in children and young animals. During a retrospective analysis of samples collected from Paraguayan children under 5 years old with diarrhea, and previously negative for rotavirus and norovirus, we detected the presence of bovine rotavirus sequences by viral metagenomics. Nucleic acid was extracted direct from stool sample and determined to be G8P[1]. The genomic analyzes revealed that the strain presents an Artiodactyl-like genome (G8-P[1]-I2-R2-C2-M1-Ax-N2-T6-E12-H3) suggesting a direct animal-to-human transmission.

Whole-genome analyses reveals the animal origin of a rotavirus G4P[6] detected in a child with severe diarrhea

Group A rotaviruses are a major cause of severe gastroenteritis in children worldwide. Currently, two rotavirus vaccines are being used in vaccination programs, and one of the factors involved in lower vaccine efficacy is the mismatch among the circulating strains and the vaccine strains. Thus, the emergence of animal strains in the human population could affect the efficacy of vaccination programs. Here we report the presence of a G4P[6] strain in a Paraguayan child presenting acute gastroenteritis in 2009. Genomic analyses revealed that the strain presents a porcine-like genome (G4-P[6]-I1-R1-C1-M1-A8-N1-T7-E1-H1), suggesting a direct animal-to-human transmission. Continuous surveillance of rotaviruses in humans and animals will help us to better understand rotavirus epidemiology and evolution.

Identification of a Broadly Cross-Reactive Epitope in the Inner Shell of the Norovirus Capsid

Noroviruses are major pathogens associated with acute gastroenteritis. They are diverse viruses, with at least six genogroups (GI-GVI) and multiple genotypes defined by differences in the major capsid protein, VP1. This diversity has challenged the development of broadly cross-reactive vaccines as well as efficient detection methods. Here, we report the characterization of a broadly cross-reactive monoclonal antibody (MAb) raised against the capsid protein of a GII.3 norovirus strain. The MAb reacted with VLPs and denatured VP1 protein from GI, GII, GIV and GV noroviruses, and mapped to a linear epitope located in the inner shell domain. An alignment of all available VP1 sequences showed that the putative epitope (residues 52–56) is highly conserved across the genus Norovirus. This broadly cross-reactive MAb thus constitutes a valuable reagent for the diagnosis and study of these diverse viruses.

Complete genome analyses of G4P[6] rotavirus detected in Argentinean children with diarrhoea provides evidence of interspecies transmission from swine

Rotaviruses are dynamic pathogens that have been shown to infect multiple species. In 2006, two G4P[6] rotavirus strains with porcine characteristics were detected in Santa Fe, Argentina. To further characterize and determine the origin of these strains, nearly the full length of their genome was sequenced. While most of the genome segments were from porcine origin, the two strains grouped in different phylogenetic clusters in five out of the 11 genes, suggesting two independent interspecies transmission events. This study expands our knowledge of G4 rotavirus and reinforces the use of complete genome analyses as a key tool for diversity and evolution mechanicisms.

Genetic characterization of a reptilian calicivirus (Cro1)

Background

Vesiviruses in the family Caliciviridae infect a broad range of animal hosts including mammals, birds, fish, amphibians and reptiles. The vesivirus Cro1 strains were isolated from diseased snakes in the San Diego zoo in 1978 and reported as the first caliciviruses found in reptiles. The goal of this study was to characterize the Cro1 strain 780032I that was isolated in cell culture from a rock rattlesnake (Crotalus lepidus) in the original outbreak.

Results

We re-amplified the original virus stock in Vero cells, and determined its full-length genome sequence. The Cro1 genome is 8296 nucleotides (nt) in length and has a typical vesivirus organization, with three open reading frames (ORF), ORF1 (5643 nt), ORF2 (2121 nt), and ORF3 (348 nt) encoding a nonstructural polyprotein, the major capsid protein precursor, and a minor structural protein, respectively. Phylogenetic analysis of the full-length genome sequence revealed that the Cro1 virus clustered most closely with the VESV species of the genus Vesivirus, but was genetically distinct (82-83% identities with closest strains).

Conclusions

This is the first description of a full-length genome sequence from a reptile calicivirus (Cro1). The availability of the Cro1 genome sequence should facilitate investigation of the molecular mechanisms involved in Cro1 virus evolution and host range.

IFN-γ signaling to astrocytes protects from autoimmune mediated neurological disability

Demyelination and axonal degeneration are determinants of progressive neurological disability in patients with multiple sclerosis (MS). Cells resident within the central nervous system (CNS) are active participants in development, progression and subsequent control of autoimmune disease; however, their individual contributions are not well understood. Astrocytes, the most abundant CNS cell type, are highly sensitive to environmental cues and are implicated in both detrimental and protective outcomes during autoimmune demyelination. Experimental autoimmune encephalomyelitis (EAE) was induced in transgenic mice expressing signaling defective dominant-negative interferon gamma (IFN-γ) receptors on astrocytes to determine the influence of inflammation on astrocyte activity. Inhibition of IFN-γ signaling to astrocytes did not influence disease incidence, onset, initial progression of symptoms, blood brain barrier (BBB) integrity or the composition of the acute CNS inflammatory response. Nevertheless, increased demyelination at peak acute disease in the absence of IFN-γ signaling to astrocytes correlated with sustained clinical symptoms. Following peak disease, diminished clinical remission, increased mortality and sustained astrocyte activation within the gray matter demonstrate a critical role of IFN-γ signaling to astrocytes in neuroprotection. Diminished disease remission was associated with escalating demyelination, axonal degeneration and sustained inflammation. The CNS infiltrating leukocyte composition was not altered; however, decreased IL-10 and IL-27 correlated with sustained disease. These data indicate that astrocytes play a critical role in limiting CNS autoimmune disease dependent upon a neuroprotective signaling pathway mediated by engagement of IFN-γ receptors.

Immunogenicity and specificity of norovirus Consensus GII.4 virus-like particles in monovalent and bivalent vaccine formulations

Noroviruses, a major cause of acute gastroenteritis worldwide, present antigenic diversity that must be considered for the development of an effective vaccine. In this study, we explored approaches to increase the broad reactivity of virus-like particle (VLP) norovirus vaccine candidates. The immunogenicity of a GII.4 "Consensus" VLP that was engineered from sequences of three genetically distinct naturally occurring GII.4 strains was examined for its ability to induce cross-reactive immune responses against different clusters of GII.4 noroviruses. Rabbits immunized with GII.4 Consensus VLPs developed high serum antibody titers against VLPs derived from a number of distinct wild-type GII.4 viruses, including some that had been circulating over 30 years ago. Because the sera exhibited low cross-reactivity with antigenically distinct GI norovirus strains, we investigated the serum antibody response to a bivalent vaccine formulation containing GI.1 (Norwalk virus) and GII.4 Consensus VLPs that was administered to animals under varying conditions. In these studies, the highest homologous and heterologous antibody titers to the bivalent vaccine were elicited following immunization of animals by the intramuscular route using Alhydrogel (Al(OH)(3)) as adjuvant. Our data indicate that the use of both genetically engineered norovirus VLPs that incorporate relevant epitopes from multiple strains and multivalent vaccine formulations increase the breadth of the immune response to diverse variants within a genotype and, thus, prove helpful in the rational design of VLP-based vaccines against human noroviruses.

Predominance of rotavirus G2P[4] and emergence of G12P[9] strains in Asunción, Paraguay, 2006-2007

Rotavirus is the most common cause of severe diarrhea in children worldwide. Monitoring the diversity of rotavirus strains is of great importance for current and future vaccination programs. To determine the diversity of rotavirus circulating in Asuncion, Paraguay, between 2006 and 2007, we carried out a molecular characterization of rotaviruses detected in children <5 years old and adults (>18 years old). We found that the most common circulating strain was G2P[4] (69/143), followed by G9P[8] (37/143). The temporal distribution of strains showed that, in children, G2P[4] was predominant in 2006, and that G2P[4] and G9P[8] were co-predominant in 2007, whereas in adults, G2P[4] was predominant in both years. Additionally, one G9P[6] and three G12P[9] strains were found in adult samples, making this the first report of these strains circulating in Paraguay. Sequence analysis of the G12P[9] strains suggests across-border migration of this strain within the southern cone of America.

Target-dependent B7-H1 regulation contributes to clearance of central nervous system infection and dampens morbidity

The neurotropic coronavirus JHM strain of mouse hepatitis virus persists in oligodendroglia despite the presence of virus-specific CD8 T cells. Expression of programmed death 1 (PD-1) and B7-H1 were studied during acute and persistent infection to examine whether this negative regulatory mechanism contributes to CNS viral persistence. The majority of CNS-infiltrating CD8 T cells expressed PD-1, with the highest levels on virus-specific CD8 T cells. Moreover, despite control of infectious virus, CD8 T cells within the CNS of persistently infected mice maintained high PD-1 expression. Analysis of virus-susceptible target cells in vivo revealed that B7-H1 expression was regulated in a cell type-dependent manner. Oligodendroglia and microglia up-regulated B7-H1 following infection; however, although B7-H1 expression on oligodendroglia was prominent and sustained, it was significantly reduced and transient on microglia. Infection of mice deficient in the IFN-gamma or IFN-alpha/beta receptor demonstrated that B7-H1 expression on oligodendroglia is predominantly regulated by IFN-gamma. Ab blockade of B7-H1 on oligodendroglia in vitro enhanced IFN-gamma secretion by virus-specific CD8 T cells. More efficient virus control within the CNS of B7-H1-deficient mice confirmed inhibition of CD8 T cell function in vivo. Nevertheless, the absence of B7-H1 significantly increased morbidity without altering demyelination. These data are the first to demonstrate glia cell type-dependent B7-H1 regulation in vivo, resulting in adverse effects on antiviral CD8 T cell function. However, the beneficial role of PD-1:B7-H1 interactions in limiting morbidity highlights the need to evaluate tissue-specific intervention strategies.

[Molecular characterization of calicivirus strains detected in outbreaks of gastroenteritis occurring in Argentina during 2005 and 2006]

In order to determine the incidence of calicivirus, rotavirus and astrovirus in outbreaks of gastroenteritis occurring in different regions of Argentina during 2005 and 2006, fecal samples from seven nonbacterial outbreaks were analyzed. A commercial ELISA was used for rotavirus detection, while RT-PCRs were used for calicivirus and astrovirus. Of the 74 samples analyzed, 20 were calicivirus positive, 17 were rotavirus positive and one was astrovirus positive. No mixed infections were detected. A partial region of the RdRp gene was sequenced in five calicivirus positive-samples; 4 of them belonged to Norovirus genus and one to Sapovirus genus. The phylogenetic analysis of norovirus-positive-samples revealed the presence of strains from genogroups GI and GII; genotypes GII-4, GII-b and GII-17 were identified within the latter. Phylogenetic the sapovirus-positive-sample revealed the presence of genotype GI-1. This study represents a follow-up of the of molecular epidemiology analysis of calicivirus associated to gastroenteritis outbreaks that have been carried out by our group since 2004, and constitutes the first report of the circulation of genotype GII-17 in Argentina.

Phylogenetic analysis of porcine rotavirus in Argentina: Increasing diversity of G4 strains and evidence of interspecies transmission

Group A rotaviruses are one of the most frequently detected viral agents associated with neonatal diarrhea in piglets. In order to characterize rotavirus (RV) strains circulating in Argentinean swine, four porcine production farms located in Buenos Aires were studied. RV strains genotyped as P[6]G4, P[6]G8 and P[1]G6 were found in piglets under 30 days of age, without diarrhea. Phylogenetic and sequence analysis of the VP7 gene from G4 strains available in databases, reveals five porcine new lineages (III-VII) and three sublineages (VIIa-VIIc). The G4 porcine Argentinean strains were grouped with a porcine RV strain isolated in Brazil and another RV strain isolated from a child with diarrhea in Mexico, constituting an American lineage (VII). On the other hand, porcine G6 and G8 were closely related to RV's circulating in Argentinean cattle and South-American camelids, respectively. The fact that G4 porcine lineages were epidemiologically related to human strains, and G6 and G8 Argentinean porcine strains were found related to bovine and South-American camelids, respectively, suggests that pigs might play a crucial role as reservoir and generator of newly adapted emerging RV strains for human and other species.

Diversity of group A rotavirus strains circulating in Paraguay from 2002 to 2005: Detection of an atypical G1 in South America

BACKGROUND

Group A rotaviruses are the main cause of severe gastroenteritis in children worldwide.

OBJECTIVES

To survey human rotavirus strains circulating in Paraguay.

STUDY DESIGN

One hundred ninety-six rotavirus-positive fecal samples collected from children up to 5 years old, from 2002 to 2005, were characterized.

RESULTS

The most common G genotype detected was G9 (36.2%), followed by G1 (34.2%), G2 (11.7%) and G4 (8.7%). Changes in the G genotype frequency were observed from year to year. The G4 genotype was predominant in 2002; G1 in 2003; and G9 from 2004 to 2005. Sequence and phylogenetic analysis of the VP7 gene from Paraguayan G1 strains suggested that the high frequency of G1 in 2003 could be due to the introduction of an atypical sub-lineage. In addition, there were amino acid changes in the variable/antigenic regions of the VP7 gene from G4 and G9 strains detected in different years.

CONCLUSIONS

This study further indicates that antigenic pressure can drive the evolution of rotaviruses, and also suggests that a vaccine that protects against the most prevalent strains and its variants, will be necessary to elicit a protective immune response against the range of rotavirus types currently circulating in Paraguay.

Genetic diversity of the VP4 and VP7 genes affects the genotyping of rotaviruses: analysis of Paraguayan strains

The introduction of different multiplex RT-PCR strategies for the characterization of field rotavirus strains has led to improvements of surveillance systems worldwide. Nevertheless, the failure or incorrect characterization of rotavirus strains by these PCR strategies, mainly due to accumulation of point mutations in the VP4 and VP7 genes, has been reported. In this work, sequence analyses of the VP4 and VP7 genes from Paraguayan G1P[8] and G4P[8] strains revealed that the high degree of similarity with the primers pNCDV and ET10 could lead to the incorrect characterization of these strains as P[1] and G10 types. Moreover, the nucleotide diversity of the VP4 gene at the 1T-1 primer binding site could be one, although not the only, reason of the failure of the P[8] typing. Therefore, the typing methods utilized by surveillance programs should be constantly evaluated and sequencing of atypical strains should become a current practice in order to confirm their real nature.

Detection of human rotavirus G9P[8] strains circulating in Argentina: phylogenetic analysis of VP7 and NSP4 genes

During the surveillance of rotavirus strains that were circulating in Argentinean children from 2000 to 2004, seven rotaviruses were detected bearing the genotype combination G9P[8]. The molecular characterization of the VP7 and NSP4 genes and the RNA migration patterns support the hypothesis that rotaviruses G9 could have been reintroduced into Argentina as a novel G9P[8] strain, rather than represent VP7 gene reassortants from G9P[6] strains that had been circulating previously in this country.

Rotavirus infection in the Paraguayan population from 2004 to 2005: high incidence of rotavirus strains with short electropherotype in children and adults

BACKGROUND

Rotavirus is considered the main viral cause of acute gastroenteritis in children in both developed and developing countries. The aim of the present study was to continue the surveillance of rotavirus in the Paraguayan population in anticipation of a rotavirus vaccination in children.

MATERIAL/METHODS

Fecal samples from infants (< or =5 years of age) and adults with diarrhea (912 and 801 samples, respectively) were collected in Paraguay during 2004-2005. Rotavirus incidence was screened by PAGE and genotyping was performed by reverse transcription (RT)-PCR.

RESULTS

Rotavirus incidence was 23.8% and 19.4% for children and adults, respectively. The rotavirus incidence was higher in the coolest and driest months of the year. Five different group A rotavirus electropherotypes were detected. Rotaviruses with a long electropherotype were the most frequently detected in children in 2004 and 2005. However, in 2005 (after six years of absence in Paraguay) rotaviruses with a short electropherotype were detected at high frequency in both children and adults. Of these, 14 samples were genotyped (11 from children and 3 from adults) and all of them showed the G2P[4] type.

CONCLUSIONS

This study reinforces the importance of continuous survey of rotavirus infection, extended to all age groups, in order to increase our knowledge about the complexity of rotavirus epidemiology.

Molecular characterization of calicivirus strains detected in outbreaks of gastroenteritis in Argentina

Eight outbreaks of acute gastroenteritis occurred in Argentina in 2004 were tested for the presence of Calicivirus, Rotavirus and Astrovirus as possible causative agents. Caliciviruses were found in 39 out of the 100 tested samples, followed by six Astrovirus-positive samples and two Rotavirus-positive samples. Thirty-seven out of the 39 Calicivirus-positive samples were typed as Norovirus while the remaining two were typed as Sapovirus. Sequence and phylogenetic analyses of 13 Norovirus-positive samples revealed the presence of strains from the genogroups GI, GII, and GIV. Six Norovirus strains were grouped with the GIV-1 strains, three with the GIIb strains, two with the Farmington Hill-cluster (GII-4) strains, and the remaining two with the GI strains. To our knowledge, this study constitutes the first report of molecular epidemiology of human Caliciviruses associated to gastroenteritis outbreaks in Argentina and the circulation of GIIb and GIV-1 strains in South-America.

Nucleotide mismatches between the VP7 gene and the primer are associated with genotyping failure of a specific lineage from G1 rotavirus strains

In recent years it was reported that the accumulation of point mutations in VP4 and VP7 genes of rotavirus strains was the main cause of the failure of the G or P-typing. Failures in the correct genotyping of G1, G2, G8, G9 and G10 rotavirus strains were reported in the most commonly used reverse transcription (RT)-PCR strategies. Collecting VP7 gene sequences of G1 rotavirus strains from databases we found that 74 (61.2 %) out of 121 G1 strains from lineage I showed the four specific mismatches at the 5' end of the 9T1-1 primer, previously associated with the failure of G1-typing. Thus, a great percentage of the G1 strains from lineage I worldwide reported could not have been typed if the Das's RT-PCR strategy were used. This analysis shows that the failure on the detection of the G1 strains could be due to the diversification of rotavirus strains in phylogenetic lineages. Therefore, the use of different RT-PCR strategies with different primer binding locations on the VP7 gene or new typing methodologies -like microarrays procedures- could be a better option to avoid the failure of the G-typing of rotavirus strains detected during surveillance programs.

[Incidence of rotavirus in adults with diarrhea in Asunción, Paraguay]

From October 2001 to March 2004, 92 out of 533 (17.3%) fecal samples of patients over 18 years of age were positive for rotavirus. There were not differences of rotavirus incidence between age groups. Although in Paraguay, rotavirus infections in children less than 5 years old present a seasonal peak pattern (since June to October), in adults rotavirus was present throughout the year with the same frequency. Results presented here reinforce the notion that rotavirus should be considered in the differential diagnosis of diarrhea in adults.

Evidence of rotavirus intragenic recombination between two sublineages of the same genotype

Rotavirus G4 prevalence increased during the past decade, with one of the highest prevalences reported during rotavirus surveillance in Argentina. Intragenotype diversity analysis has led to its subdivision into lineages (I and II) and sublineages (Ia-Id). On analysis of Argentine and G4 VP7 sequences from other locations, one Argentine strain (ArgRes1723) appeared to be an intermediate between G4 sublineages Ib and Ic. Similarity and bootscanning analyses and Sawyer's test were carried out to demonstrate the recombinant nature of this strain. It was concluded that intragenic recombination occurred between sequences of sublineages Ib and Ic, with a crossover point between nucleotide positions 336 and 387. This study constitutes the first report of a mechanism of evolution in rotaviruses that is currently considered unusual - a recombination event between two strains of the same rotavirus genotype. These results will help increase current knowledge about rotavirus evolution and divergence, improving our understanding of the adaptation mechanisms used by these viruses.