NoV Infection Research Articles

Optimization of one-step real-time reverse transcription-polymerase chain reaction assays for norovirus detection and molecular epidemiology of noroviruses in Thailand

Noroviruses (NoVs) are an important human pathogen associated with acute viral gastroenteritis worldwide. NoVs display a significant amount of genetic heterogeneity, making it difficult to develop comprehensive detection assays. In this study, primer sets and probes were designed for a TaqMan®-based real-time reverse transcription-polymerase chain reaction (RT-PCR) for norovirus detection purposes. The assay was optimized and utilized as a multiplex real-time RT-PCR assay for genogroup I (GI) detection, and a singleplex real-time RT-PCR assay for genogroup II (GII) detection. The assays showed high specificity for NoV detection and no cross-reactivity was observed between GI and GII. The detection limit of the assay was as low as 10 and 50 RNA copies per reaction for GI and GII, respectively. The optimized protocol was employed to assess the presence of NoV strains in clinical samples collected throughout Thailand during December 2005 to November 2006. The percentage of NoV infections among children with acute gastroenteritis (case) was 23.8% (119/500) and for children without acute gastroenteritis (control) it was 6.8% (30/441). The frequency of NoV infections varied geographically, with the highest frequency observed in the central region and the lowest frequency in the northern region (P>0.0001). Of the 149 positive case and control specimens, GII was found to be the predominant genogroup (98.6%). Partial capsid sequences were successfully obtained from 67 NoV-positive specimens and a phylogenetic analysis was performed to genotype the viral strains. GII.4 was the most common genotype detected.

Pediatric norovirus infection

Noroviruses (NoVs) are among the most frequent causes of acute pediatric gastroenteritis. Although the disease is often self-limiting and recovery is the rule, it constitutes an important health problem because of its highly contagious nature and the high rate of morbidity. NoVs are responsible for 47-96 % of outbreaks of acute pediatric gastroenteritis, and 5-36 % of sporadic cases. NoV-induced gastroenteritis is a frequent cause of hospitalization, and severe and sometimes fatal cases have been reported in immunocompromised children. The increasing recognition of NoVs as the cause of pediatric disease and the limited success in preventing outbreaks have led to consideration of vaccines. However, while awaiting the development of a vaccine, there is an urgent need for more epidemiological data concerning childhood NoV infection, including the impact of NoVs on different age groups, the possible etiological role of NoVs in infections other than gastroenteritis, and the socioeconomic impact of NoVs on households.

Median infectious dose of human norovirus GII.4 in gnotobiotic pigs is decreased by simvastatin treatment and increased by age

Human noroviruses (NoVs), a major cause of viral gastroenteritis, are difficult to study due to the lack of a cell-culture and a small-animal model. Pigs share with humans the types A and H histo-blood group antigens on the intestinal epithelium and have been suggested as a potential model for studies of NoV pathogenesis, immunity and vaccines. In this study, the effects of age and a cholesterol-lowering drug, simvastatin, on the susceptibility of pigs to NoV infection were evaluated. The median infectious dose (ID50) of a genogroup II, genotype 4 (GII.4) 2006b variant was determined. The ID50 in neonatal (4-5 days of age) pigs was ≤2.74×10(3) viral RNA copies. In older pigs (33-34 days of age), the ID50 was 6.43×10(4) but decreased to <2.74×10(3) in simvastatin-fed older pigs. Evidence of NoV infection was obtained by increased virus load in the intestinal contents, cytopathological changes in the small intestine, including irregular microvilli, necrosis and apoptosis, and detection of viral antigen in the tip of villi in duodenum. This GII.4 variant was isolated in 2008 from a patient from whom a large volume of stool was collected. GII.4 NoVs are continuously subjected to selective pressure by human immunity, and antigenically different GII.4 NoV variants emerge every 1-2 years. The determination of the ID50 of this challenge virus is valuable for evaluation of protection against different GII.4 variants conferred by NoV vaccines in concurrence with other GII.4 variants in the gnotobiotic pig model.

Noroviruses and histo‐blood groups: the impact of common host genetic polymorphisms on virus transmission and evolution

Noroviruses (NoVs) are recognized as a leading cause of human gastroenteritis worldwide. Infection occurs following the ingestion of contaminated food or, most often, through direct contact from person to person. However, not all individuals are equally sensitive to these viruses. Indeed, NoVs use glycans of the ABH and Lewis histo-blood group antigen family (HBGAs) as attachment factors. At the epithelial level, the synthesis of these HBGAs requires the action of several glycosyltransferases that are encoded by the ABO, FUT2, and FUT3 genes. The combined polymorphism at these three loci dictates sensitivity to NoV infection because the attachment profile to these glycans varies among strains. Structural analysis of the capsid protein interaction with HBGAs reveals distinct modes of binding for strains of genogroups I and II but high conservation within each genogroup, whereas minor amino acid changes are sufficient to generate modifications of HBGA-binding specificities or affinities. Such modifications therefore induce changes in the spectrum of susceptible individuals. Studies of NoV-HBGA interactions together with phylogenetic analyses and the epidemiologic survey of strains indicate that NoV transmission and evolution depend on both the establishment of herd immunity and the genetic resistance of many individuals, which confers herd innate protection by restricting NoV circulation.

Clinical and Epidemiologic Characteristics of Norovirus GII.4 Sydney during Winter 2012–13 in Beijing, China following Its Global Emergence

BackgroundLimited information is available on the molecular epidemiology of GII.4 Sydney-associated diarrhea in China in the winter of 2012–13 during the global epidemic associated with the emergence of GII.4 Sydney.MethodsFecal specimens collected from 171 diarrhea outpatients (one from each) between late October 2012 and the middle of March 2013 were examined for NoV by reverse transcription-polymerase chain reaction and sequences corresponding to both the NoV partial polymerase and partial capsid regions were analyzed phylogenetically. Clinical characteristics of GII.4 Sydney cases versus other NoV-positive cases detected in a previous study were compared statistically.ResultsTwenty-six (15.2%, 26/171) outpatients with diarrhea were infected with NoV. Twenty-two of the 26 (84.6%) identified NoV strains clustered into GII.4 Sydney. There was a significant difference in symptoms of fever (χ2, P<0.05 ), abdominal pain (χ2, P<0.05 ) and diarrhea frequency (Mann-Whitney U test, P<0.05) between the GII.4 Sydney case group and other NoV-positive case group.ConclusionsThe new NoV variant, GII.4 Sydney, has been circulating in Beijing, China and became the predominant strain in the winter of 2012–13. GII.4 Sydney causes severe fever, abdominal pain and higher diarrhea frequency clinically compared to other NoV infections.

Norovirus GII.4/Sydney/2012 in Italy, Winter 2012–2013

To the Editor: Noroviruses (NoVs) are the major cause of acute gastroenteritis in children and adults; they are responsible for sporadic cases and outbreaks of gastroenteritis in various epidemiologic settings. NoVs can be classified genetically into at least 5 genogroups, GI to GV (1). Although >30 genotypes within genogroups GI, GII, and GIV can infect humans (2), a single genotype, GII.4, has been associated with most NoV-related outbreaks and sporadic cases of gastroenteritis worldwide (3). GII.4 NoV strains continuously undergo genetic/antigenic diversification and periodically generate novel strains through accumulation of punctate mutations or recombination. New GII.4 variants emerge every 2–3 years (4). Increased incidence of NoV-related illness and/or outbreaks in various countries in late 2012 has been related to the emergence of a novel GII.4 variant, Sydney 2012. This variant was first identified in March 2012 in Australia (5). The Italian Study Group for Enteric Viruses (ISGEV; http://isgev.net) monitors the epidemiology of enteric viruses in children through hospital-based surveillance (6–8). NoVs are monitored and characterized by multitarget analysis in the diagnostic regions A (open reading frame 1, polymerase) and C (open reading frame 2, capsid) of the NoV genome (9) and interrogation of the Norovirus Typing Tool database (www.rivm.nl/mpf/norovirus/typingtool). During November 2011–March 2012, the prevalence of sporadic NoV infections detected (in samples from newborns, infants, and children up to 5 years of age) by real-time reverse transcription PCR was 22.2% (121/545). A subset (≈50%) of the NoV-positive samples representative of the whole winter period was selected for sequence analysis, and 48 were successfully characterized in region A and region C. Among these 48 NoV strains, 20 (41.7%) were characterized as the variant GII.4 New Orleans 2009, a smaller number, 6 (12.5%), displayed a New Orleans 2009 polymerase (pol) but 2 distinct GII.4 capsid sequences, which were not typeable in the Norovirus Typing Tool database, and only 2 (4.2%) GII.4 strains of the variant Den Haag 2006b were detected. Moreover, 4 sporadic cases in November 2011 and January 2012 and a small outbreak in February 2012 were related to a GII.Pe_GII.4 recombinant strain. After the set of sequences of GII.4 variants from the Norovirus Typing Tool database was updated (access to the updated database: April 11, 2013), 5 (10.4%) GII.Pe_GII.4 recombinant strains were characterized as variant Sydney 2012. From April through October 2012, a total of 56 (7.6%) NoV-positive samples were detected from 737 analyzed samples, of which 34 (60.7%) NoV-positive samples could be sequenced. Of these, 41.2% were characterized as GII.3 (mostly with a GII.Pb pol), 26.5% as GII.Pg_GII.1, and 17.6% as GII.4 variants. From spring to fall 2012, the variant New Orleans 2009 became the predominant GII.4 strain, and the variant Sydney 2012 strain apparently disappeared. During November–December 2012 and January 2013, ISGEV detected NoV infection in 90 (28.9%) of 311 children hospitalized for gastroenteritis. This finding is comparable to a prevalence of 25.2% in the same period (November–January) of the 2011–12 winter season. A representative subset of 45 samples was randomly selected for sequencing, and 26 (74.3%) of 35 fully typed strains were characterized as GII.4 Sydney 2012, which suggested that the new NoV variant had become the predominant strain in Italy. Our findings seem to mirror observations of a report from Denmark that documented the onset and circulation at low prevalence of the variant GII.4 Sydney 2012 at the beginning of 2012 with a marked increase in the prevalence only by the end of 2012 (10). Our surveillance detected the emergence of this variant in Italy at the end of 2011 and provided us with one of the earliest strains of the variant GII.4 Sydney 2012. This novel variant has a common ancestor with the NoV GII.4 variants Apeldoorn 2008 and New Orleans 2009 and has several amino acid changes on the main epitope in the capsid P2 domain (10). Sequence analysis of these early strains of the GII.4 variant Sydney 2012 could help clarify the mechanisms driving its global emergence and spread. Continued surveillance for NoV infections through ISGEV and additional data on clinical and epidemiologic features will enable further assessment of the public health implications of the new variant GII.4 Sydney 2012 in Italy.

Genetic susceptibility to norovirus infection and herd innate protection.

Norovirus (NoVs) are recognized as a leading cause of human gastroenteritis worldwide. Infection takes place following ingestion of contaminated food or most often through direct contact from person to person. However, not all individuals are equally sensitive to these viruses. Indeed, NoVs use ABH and Lewis glycans of the histo-blood group antigen family (HBGAs) as ligands. At the epithelial level synthesis of these HBGAs requires the action of several glycosyltransferases encoded by the ABO, FUT2 and FUT3 genes. Since the attachment profile to these glycans varies from strain to strain, the combined polymorphism at these three loci dictates sensitivity to NoV infection. Studies of the NoV-HBGA interactions together with phylogenetic analyses and the epidemiologic follow-up of strains indicate that NoVs transmission and evolution depends both on the establishment of herd immunity and on the genetic resistance of many individuals that contributes to restrict NoVs circulation, confering a herd innate proctection.

Clinical and molecular epidemiology of norovirus infection in adults with acute gastroenteritis in Ji’nan, China

Acute gastroenteritis caused by human noroviruses (NoVs) has become an important public health problem worldwide. This study was carried out to investigate the rates of NoV infections and the genetic characteristics of NoVs in adult outpatients with acute gastroenteritis in Ji'nan, a large eastern city in China. A total of 480 fecal samples were collected from outpatients at the Shandong University Qilu Hospital between June 2010 and May 2011. Of the collected samples, 42 (42/480, 8.75 %) were positive for NoVs by RT-PCR, and seven different genotypes were identified: GI-1, GI-4, GII-1, GII-3, GII-4, GII-6 and GII-13, of which GII-4 was the most prevalent (29/42, 69.0 %). Phylogenetic and Simplot analyses showed that three recombinant strains were detected: two GII-4 polymerase/GII-3 capsid recombinants and one GII-6 polymerase/GII-4 capsid recombinant. This study indicated that NoV was a common causative agent of sporadic acute gastroenteritis in adults in Ji'nan, China, and that NoV GII-4 was the predominant strain during this period. Three recombinant strains were identified in which GII-6 polymerase/GII-4 capsid was detected for the first time in China.

Norovirus virus-like particle vaccines for the prevention of acute gastroenteritis

Noroviruses (NoVs) are the most common cause of nonbacterial acute gastroenteritis in humans worldwide. These highly infectious viruses were, until recently, commonly thought to cause a mild, self-limiting disease in healthy individuals, but increasing epidemiology shows that the incidence and severity of illness due to NoV infection is substantial and similar to diseases where immunization is widely recommended. Human NoV challenge studies have identified carbohydrate histo-blood group antigen expression as an important human susceptibility factor for many strains and correspondingly, that antibodies which block carbohydrate virus binding represent a potential correlate of protection against NoV infection and illness. Since human NoVs do not replicate in cell culture, there are numerous challenges to the development of a vaccine to prevent illness or infection. However, the development of NoV virus-like particles (VLPs) has enabled significant progress toward effective vaccine candidates designed to protect against multiple circulating NoV strains. Vaccination with NoV VLP vaccines has been shown to both induce antibodies that block virus-derived VLP carbohydrate binding and protect against homologous viral challenge in a human clinical study.

Evaluation of anti-norovirus IgY from egg yolk of chickens immunized with norovirus P particles

Noroviruses (NoVs) are a leading cause of epidemic acute gastroenteritis affecting millions of people worldwide. Understanding of NoV remains limited due to the lack of a cell culture system and small animal models. Currently, there are no effective vaccines or antivirals against NoVs. In this study, an approach for large-scale production of anti-NoV antibodies for use as a potential treatment for NoV disease using passive immunization was evaluated. NoV-specific immunoglobulins (IgYs) were produced by immunizing chickens with NoV P particles. The birds continuously produced high titers of antibodies in their eggs for at least 3months, in which NoV-specific antibody levels reached 4.7-9.2mg/egg yolk. The egg yolk antibodies strongly reacted with NoV P particles by both ELISA and Western blot and blocked NoV virus-like particle (VLP) and P particle binding to the histo-blood group antigen (HBGA) receptors with a BT(50) of about 1:800. The blocking activity of the chicken IgY remained after an incubation at 70°C for 30min or treatments at pH 4-9 for 3h. These data suggested that chicken IgY could be a practical strategy for large-scale production of anti-NoV antibodies for potential use as passive immunization against NoV infection, as well as for diagnostic purposes.

Unrecognized Norovirus Infections in Health Care Institutions and Their Clinical Impact

Noroviruses (NoVs) have emerged as the leading cause of acute viral gastroenteritis (GE) in humans. Although diagnostic facilities have greatly improved, significant underdiagnosis of NoV in hospitals may still occur, thereby increasing clinical burden and nosocomial spread. We evaluated the underdiagnosis of sporadic NoV infections in a tertiary care hospital and estimated its clinical impact. From December 2008 until July 2009, fecal samples specifically referred for bacterial but not viral examination were retrospectively tested for NoV by real-time PCR. The clinical and virological data from patients with undiagnosed NoV infection (missed patients) were evaluated and compared with those from patients with recognized NoV. During the study period, 45 patients with undiagnosed NoV were detected, whereas 50 patients were regularly diagnosed. The missed NoV cases were more frequently adults than children (80% versus 46%; P < 0.001). The viral load levels did not differ between the diagnosed and missed patients, but missed patients more frequently presented without diarrhea (20% versus 4%; P < 0.07). The newly admitted missed NoV cases with GE underwent more diagnostic imaging (24% versus 4%; P < 0.01) and tended to be hospitalized longer. When missed-NoV patients were included, the number of nosocomial clusters doubled and missed patients were index cases in 5 of the 6 clusters. These data indicate that NoV infections are frequently missed despite routine laboratory testing and demonstrate that underdiagnosis of NoV patients is associated with costly abdominal imaging and nosocomial clustering. Awareness of NoV infection in adult patients and education about the importance of viral GE should be increased.

Molecular epidemiology of canine norovirus in dogs from Portugal, 2007–2011

BackgroundCanine noroviruses (NoVs) have been recently described in south European countries and associated with outbreaks of diarrhea in kennels. Unlike human NoV which are known as an important cause of acute gastroenteritis, little is known about the role of canine NoV as pathogens in dogs as well as its epidemiological features.ResultsFrom 2007–2011, 256 stool samples were collected from dogs across Portugal and tested by RT-PCR for canine NoV. Viral fecal shedding was found to be 23% (60/256). All sequences contained the GLPSG amino acid motif characteristic of the RNA-dependent RNA-polymerase gene of NoVs and had a high nucleotide identity (range 98%–100%) to the canine NoV first described in Portugal. The highest shedding rate was detected during the winter months.ConclusionsThis study shows that canine NoV infection is endemic in the dog population of Portugal. Peak shedding was detected in the winter months, a well-known epidemiologic feature of human NoV infections.

Contribution of Intra- and Interhost Dynamics to Norovirus Evolution

Norovirus (NoV) is an emerging RNA virus that has been associated with global epidemics of gastroenteritis. Each global epidemic arises with the emergence of novel antigenic variants. While the majority of NoV infections are mild and self-limiting, in the young, elderly, and immunocompromised, severe and prolonged illness can result. As yet, there is no vaccine or therapeutic treatment to prevent or control infection. In order to design effective control strategies, it is important to understand the mechanisms and source of the new antigenic variants. In this study, we used next-generation sequencing (NGS) technology to investigate genetic diversification in three contexts: the impact of a NoV transmission event on viral diversity and the contribution to diversity of intrahost evolution over both a short period of time (10 days), in accordance with a typical acute NoV infection, and a prolonged period of time (288 days), as observed for NoV chronic infections of immunocompromised individuals. Investigations of the transmission event revealed that minor variants at frequencies as low as 0.01% were successfully transmitted, indicating that transmission is an important source of diversity at the interhost level of NoV evolution. Our results also suggest that chronically infected immunocompromised subjects represent a potential reservoir for the emergence of new viral variants. In contrast, in a typical acute NoV infection, the viral population was highly homogenous and relatively stable. These results indicate that the evolution of NoV occurs through multiple mechanisms.

Tannic acid inhibited norovirus binding to HBGA receptors, a study of 50 Chinese medicinal herbs

Noroviruses (NoVs) are the leading cause of viral acute gastroenteritis affecting people of all ages worldwide. The disease is difficult to control due to its widespread nature and lack of an antiviral or vaccine. NoV infection relies on the interaction of the viruses with histo-blood group antigens (HBGAs) as host receptors. Here we investigated inhibition effects of Chinese medicinal herbs against NoVs binding to HBGAs for potential antivirals against NoVs. Blocking assays was performed using the NoV protrusion (P) protein as NoV surrogate and saliva as HBGAs. Among 50 clinically effective Chinese medicinal herbs against gastroenteritis diseases, two herbs were found highly effective. Chinese Gall blocked NoV P dimer binding to type A saliva at IC50=5.35μg/ml and to B saliva at IC50=21.7μg/ml. Similarly, Pomegranate blocked binding of NoV P dimer to type A saliva at IC50=15.59μg/ml and B saliva at IC50=66.67μg/ml. Literature data on preliminary biochemistry analysis showed that tannic acid is a common composition in the extracts of the two herbs, so we speculate that it might be the effective compound and further studies using commercially available, highly purified tannic acid confirmed the tannic acid as a strong inhibitor in the binding of NoV P protein to both A and B saliva (IC50≈0.1μM). In addition, we tested different forms of hydrolysable tannins with different alkyl esters, including gallic acid, ethyl gallate, lauryl gallate, octyl gallate and propyl gallate. However, none of these tannins-derivatives revealed detectable inhibiting activities. Our data suggested that tannic acid is a promising candidate antiviral against NoVs.

Norovírus: uma visão geral

Although noroviruses (NoVs) were the first viral agents linked to gastrointestinal disease, for a long time they have been considered secondary cause of gastroenteritis, second to rotaviruses as etiologic agents. The development of molecular techniques in diagnosing NoV provided a clearer insight into the epidemiological impact of these viruses, which are currently recognized not only as the leading cause of non-bacterial gastroenteritis outbreaks, but also as a major cause of sporadic gastroenteritis in both children and adults. This review focuses on the required knowledge to understand their morphology, genetics, transmission, pathogenesis, and control. Since no vaccine is available, prevention of NoV infection relies mainly on strict community and personal hygiene measures.

Clinical and Molecular epidemiologic analyses of norovirus‐associated sporadic gastroenteritis in adults from Beijing, China

Noroviruses (NoVs) are a major cause of nonbacterial acute gastroenteritis. The molecular epidemiology of NoV infections in China has not been well characterized. To study the incidence of NoV infections and the nature of the circulating NoV genotypes, 403 specimens were collected from adult outpatients with acute gastroenteritis in Beijing, China, between October 2007 and September 2008. Samples were examined for NoV by reverse transcriptase-polymerase chain reaction (RT-PCR) and sequences corresponding to both the NoV polymerase and capsid regions were characterized. Among the 403 specimens, 48 (11.9%) were positive for NoV and 1/3 NoV-associated gastroenteritis cases occurred during the colder months (November and December). Based on polymerase region sequences, 6 NoV genotypes (GII-4, GII-b, GII-6, GI-2, GI-3, and GI-4) were identified with GII-4 2006b being the most predominant genotype (37/48, 77.1%). Eleven distinct genotype sequences in polymerase and capsid regions were identified, indicating a genetic diversity among NoV isolates. This study suggested NoVs were an important pathogen responsible for sporadic acute gastroenteritis in adults in Beijing, China.

Intranasal norovirus vaccination shows efficacy in preventing acute gastroenteritis following a live GI.1 NoV challenge (106.5)

Abstract NoVs are a common cause of both epidemic and endemic AGE. Currently, no vaccine is available to prevent illness. Vaccination with an IN GI.1 NoV virus-like particle (VLP) vaccine (adjuvanted with chitosan and monophosphoryl lipid A) was followed by a homologous viral challenge. The trial employed a randomized, double-blind, placebo-controlled design for assessing safety, immunogenicity and efficacy against AGE and infection. Two-doses of vaccine or placebo IN 3 weeks apart were administered to healthy adults 18-49 years of age. At least 3 weeks later ~10 HID50 of a GI.1 challenge virus was administered to subjects who were then monitored for illness and infection. Two doses of the NoV VLP vaccine were administered to 90 subjects with the vaccine being well tolerated. The per protocol (PP) population was 77 of the 84 persons who completed the challenge. Of the 84, 64% of vaccinees had a &amp;gt;4-fold serum IgA response, none receiving placebo. In the PP analysis the incidence of AGE decreased from 69% to 37% by vaccination and infection was reduced from 82% to 61%. Efficacy against illness was 47% (95% CI, 15-67%) and against infection was 26% (95% CI, 1-36%) relative to placebo and severity of illness was also reduced. Of note, protection from NoV illness and infection correlated with the level of 50% HBGA blocking activity prior to challenge. We report that a NoV vaccine candidate can prevent AGE and that an IN-delivered vaccine can prevent illness due to an enteric pathogen.

Prevalence of norovirus GII‐4 antibodies in Finnish children

Noroviruses (NoVs) are the second most common cause of viral gastroenteritis after rotavirus in children. NoV genotype GII-4 has emerged as the major type not only in outbreaks of NoV gastroenteritis but also endemic gastroenteritis among infants and young children worldwide. Using baculovirus-insect cell system virus-like particles (VLPs) of NoV genotype GII-4 and an uncommon genotype GII-12 were produced. These VLPs were used in enzyme-linked immunosorbent assays (ELISA) for detection of NoV-specific immunoglobulin G (IgG) and IgA antibodies in 492 serum specimens from Finnish children 0-14 years of age collected between 2006 and 2008. NoV IgG antibody prevalence was 47.3% in the age group 7-23 months and increased up to 91.2% after the age of 5 years. Avidity of NoV IgG antibodies was low in the primary infections while high avidity antibodies were detected in the recurrent infections of the older children. In GII-4 infections, the homologous antibody response to GII-4 VLPs was stronger than to GII-12 VLPs but cross-reactivity between GII-4 and GII-12 was observed. Binding of GII-4 VLPs to a putative carbohydrate antigen receptor H-type 3 could be blocked by sera from children not infected with NoV during a waterborne outbreak of acute gastroenteritis. Therefore, protection against NoV infection correlated with strong blocking activity.

Molecular epidemiology of noroviruses detected in seasonal outbreaks of acute nonbacterial gastroenteritis in Osaka City, Japan, from 1996–1997 to 2008–2009

In seasons from 1996-1997 through 2008-2009, noroviruses (NoVs) were detected in 505 outbreaks (71%) of nonbacterial gastroenteritis in Osaka City, Japan using molecular diagnosis with reverse transcription (RT)-PCR or real-time RT-PCR. The occurrences of NoV-associated outbreaks were related with the cold season during November-March (85.3%), and occasionally small epidemics of NoVs occurring during April-June were observed. Oyster-associated outbreaks were dominant transmission modes (25-61.1%) before the 2003-2004 season, and decreased (5-20.5%) from the 2003-2004 season, although outbreaks attributable to food-borne transmission (except for oysters) and person-to-person contact increased from the 2003-2004 season. The NoV strains were characterized into genotypes based on sequence analysis of partial capsid regions. Genotyping analyses identified at least 30 genotypes (12 in genogroup I [GI] and 18 in genogroup II [GII]) of NoV. The most common genotype was GII.4 (44.6%), followed in order by GII.3, GII.6, GII.2, and GII.5. The number of GII.4 NoVs increased greatly from the 2003-2004 season, eventually comprising a large share among the NoV- associated outbreaks (97.4%) of the 2006-2007 season. Occasional increased prevalence of genotypes other than GII.4 was observed during this study period. This study showed the appearance, spread, and disappearance of various genotypes and the change of NoV epidemic in a limited geographic region. Continuous NoV molecular surveillance is important for understanding NoV infections and for improving measures for their control and prevention.

Emerging norovirus GII.4 2008 variant detected in hospitalised paediatric patients in South Africa

Background Noroviruses (NoVs) are important enteric pathogens that cause gastroenteritis worldwide. The first documented NoV outbreaks in South Africa (SA) were described in 1993. The current NoV prevalence and circulating genotypes are unknown. SA lacks NoV outbreak reporting systems and therefore the number and impact of NoV infections is underestimated. Objectives This study aimed to determine the prevalence and genetic diversity of NoV infections in hospitalised paediatric patients with gastroenteritis in SA during 2008. Study design Stool specimens referred for virological analysis from hospitalised children ≤13 years, with gastroenteritis, were screened for rotavirus, human adenovirus and human astrovirus by enzyme immunoassay and for NoV genogroup I (GI), II (GII) and sapovirus by real-time RT-PCR. NoV strains were genotyped, and variants identified, based on sequence and phylogenetic analyses of the 5′ end or the full length of the capsid gene, respectively. Results Rotavirus was the most prevalent virus detected in 24.2% (61/252) of specimens, followed by NoV in 14.3% (35/245) and adenovirus, astrovirus and sapovirus in 9.6%, 6.7% and 4% of specimens, respectively. NoVs were only detected in children ≤2 years. The GII NoVs (89%) predominated and eight types were identified with GII.4 (43%) detected most frequently. The emerging 2008 GII.4 variant represented 80% of the GII.4 strains. Conclusions A diverse range of NoV genotypes were identified in hospitalised children with gastroenteritis. The 2008 GII.4 variant was the most frequently detected strain in the study. This is the first report of NoV GII.4 viruses in SA.