The Antigenic Topology of Norovirus as Defined by B and T Cell Epitope Mapping: Implications for Universal Vaccines and Therapeutics

Human norovirus (HuNoV) is the leading cause of acute nonbacterial gastroenteritis. Vaccine design has been confounded by the antigenic diversity of these viruses and a limited understanding of protective immunity. We reviewed 77 articles published since 1988 describing the isolation, function, and mapping of 307 unique monoclonal antibodies directed against B cell epitopes of human and murine noroviruses representing diverse Genogroups (G). Of these antibodies, 91, 153, 21, and 42 were reported as GI-specific, GII-specific, MNV GV-specific, and G cross-reactive, respectively. Our goal was to reconstruct the antigenic topology of noroviruses in relationship to mapped epitopes with potential for therapeutic use or inclusion in universal vaccines. Furthermore, we reviewed seven published studies of norovirus T cell epitopes that identified 18 unique peptide sequences with CD4- or CD8-stimulating activity. Both the protruding (P) and shell (S) domains of the major capsid protein VP1 contained B and T cell epitopes, with the majority of neutralizing and HBGA-blocking B cell epitopes mapping in or proximal to the surface-exposed P2 region of the P domain. The majority of broadly reactive B and T cell epitopes mapped to the S and P1 arm of the P domain. Taken together, this atlas of mapped B and T cell epitopes offers insight into the promises and challenges of designing universal vaccines and immunotherapy for the noroviruses.

Molecular Epidemiology of Genogroup II Noroviruses Infection in Outpatients with Acute Gastroenteritis in Nanjing, China (2010–2013)

Objective.Human noroviruses (NoVs) of genogroup II are the most common strains detected in sporadic cases of acute nonbacterial gastroenteritis in outpatients in Nanjing. To gain insight into the molecular epidemiology of GII strains, we analyzed 75 positive NoV cases from 2010 to 2013.Methods.The sporadic cases were detected by real-time PCR with specific primers and probes to human NoVs of genogroup I or II, human sapovirus, human rotavirus, human astrovirus, and human enteric adenovirus. Human NoVs of genogroup II were further studied by VP1 amplification (RT- PCR), cloning, sequencing, and phylogenetic analysis.Results.Rotavirus and human NoVs were more frequently detected in all the cases from 2010 to 2013. Human NoVs infection was more frequent since 2011 and more frequent than rotavirus infection after 2012. Out of the 75 NoV cases of genogroup II, there were 5 GII.6, 11 GII.3, and 59 GII.4. Of the 59 GII.4, 27 cases were previous GII.4.2006b strains that circulated between 2010 and 2012; while 32 cases were the newly emerging GII.4 strains GII.4.2012 from 2011 to 2013.Conclusion.Our data confirm other studies on the rapid emergence and displacement of highly virulent GII.4 strains.

Genetic Analysis of the Capsid Gene of Genotype GII.2 Noroviruses

ABSTRACT Noroviruses (NoVs) are considered to be a major cause of acute nonbacterial gastroenteritis in humans. The NoV genus is genetically diverse, and genotype GII.4 has been most commonly identified worldwide in recent years. In this study we analyzed the complete capsid gene of NoV strains belonging to the less prevalent genotype GII.2. We compared a total of 36 complete capsid sequences of GII.2 sequences obtained from the GenBank (n = 5) and from outbreaks or sporadic cases that occurred in The Netherlands (n = 10) and in Osaka City, Japan (n = 21), between 1976 and 2005. Alignment of all capsid sequences did not show fixation of amino acid substitutions over time as an indication for genetic drift. In contrast, when strains previously recognized as recombinants were excluded from the alignment, genetic drift was observed. Substitutions were found at five informative sites (two in the P1 subdomain and three in the P2 subdomain), segregating strains into five genetic groups (1994 to 1997, 1999 to 2000, 2001 to 2003, 2004, and 2005). Only one amino acid position changed consistently between each group (position 345). Homology modeling of the GII.2 capsid protein showed that the five amino acids were located on the surface of the capsid and close to each other at the interface of two monomers. The data suggest that these changes were induced by selective pressure, driving virus evolution. Remarkably, this was observed only for nonrecombinant genomes, suggesting differences in behavior with recombinant strains.

Major Change in the Predominant Type of “Norwalk-Like Viruses” in Outbreaks of Acute Nonbacterial Gastroenteritis in Osaka City, Japan, between April 1996 and March 1999

In Osaka City, Japan, between April 1996 and March 1999, a total of 350 fecal specimens from 64 outbreaks of acute nonbacterial gastroenteritis were examined to investigate infection by “Norwalk-like viruses” (NLVs). By reverse transcription (RT)-PCR, 182 samples (52.0%) from 47 outbreaks (73.4%) were NLV positive. During those three years, the incidence of NLV-associated outbreaks showed seasonality, being higher during January to March (winter to early spring). The ingestion of contaminated oysters was the most common transmission mode (42.6%). The amplicons of the 47 outbreak strains that were NLV positive by RT-PCR were tested using Southern hybridization with four probe sets (Ando et al., J. Clin. Microbiol. 33:64–71, 1995). Forty of the outbreak strains were classified as 4 probe 1-A (P1-A) strains, 6 P1-B strains, 10 P2-A strains, 17 P2-B strains, and 3 untypeable strains, and the other 7 outbreaks were determined to be mixed-probe-type strains. Probe typing and partial sequence analysis of the outbreak strains indicated that a predominant probe type of NLVs in Osaka City had drastically changed; P2-B strains (77.8%) with multiple genetic clusters were observed during the 1996–97 season, the P2-A common strain (81.3%) related to the Toronto virus cluster was observed during the 1997–98 season, and P1-B strains (75.0%) with a genetic similarity were observed during the 1998–99 season. For the three untypeable outbreak strains (96065, 97024, and 98026), the 98026 outbreak strain had Southampton virus (SOV)-like sequences, and each of the other outbreak strains had a unique 81-nucleotide sequence. Newly designed probes (SOV probe for the 98026 outbreak strain and the 96065 probe for the 96065 and 97024 outbreak strains) were hybridized with relative strains and without other probe type strains. The prevalent NLV probe types in Osaka City during those three years were classified in six phylogenetic groups: P1-A, P1-B, P2-A, P2-B, SOV, and 96065 probe types.

An Outbreak of Acute Nonbacterial Gastroenteritis in a Nursing Home

Objective:To determine risk factors for and modes of transmission of an outbreak of acute nonbacterial gastroenteritis among residents and staff in a nursing home.Design:Cohort study of residents and questionnaire survey of employees.Setting:One hundred twenty-bed nursing home in Alabama.Patients:From July 11,1991, through July 25,1991,77 of 120 residents (attack rate = 64%) and at least 14 of 49 employees (minimum attack rate = 29%) developed acute gastroenteritis characterized by vomiting and diarrhea; few residents developed fever > 100°F. Nine residents required intravenous rehydration, and 2 residents died.Results:The risk of developing illness was greater for female residents (64/92 versus 13/28; relative risk [RR] = 1.5; 95% confidence interval [CI95 ]=1.0-2.3) and for employees who reported handling residents' soiled linen, stools, or vomitus more frequently (>5 times a shift versus ≥ 5 times a shift: 7/13 versus 7/31; RR=2.4; CI95 = 1.1-5.4). Direct transmission of infection, probably via person-to-person spread, sustained the outbreak. Temporal clustering analysis demonstrated that the risk of becoming ill 1 or 2 days after a roommate became ill was significantly greater than that of becoming ill at other times during the outbreak (RR= 2.2; CI95 = 1.3-3.8). No Salmonella or Shigella species, ova, or parasites were identified from 12 fecal specimens obtained from ill residents.Conclusions:Although stool and serum specimens were not available for viral studies, the clinical symptoms and incubation period were consistent with illness due to Norwalk-like viral agents. This outbreak emphasizes the severity of acute nonbacterial gastroenteritis among elderly and debilitated residents of nursing homes and the need for prompt use of enteric precautions in controlling outbreaks of gastroenteritis in these facilities.