Swine Norovirus: Past, Present, and Future

Norovirus, an ssRNA + virus of the family Caliciviridae, is a leading disease burden in humans worldwide, causing an estimated 600 million cases of acute gastroenteritis every year. Since the discovery of norovirus in the faeces of swine in Japan in the 1990s, swine norovirus has been reported in several countries on several continents. The identification of the human-associated GII.4 genotype in swine has raised questions about this animal species as a reservoir of norovirus with zoonotic potential, even if species-specific P-types are usually detected in swine. This review summarises the available data regarding the geographic distribution of norovirus in swine, the years of detection, the genotype characterisation, and the prevalence in specific production groups. Furthermore, we discuss the major bottlenecks for the detection and characterisation of swine noroviruses.

Birth Cohort Studies Assessing Norovirus Infection and Immunity in Young Children: A Review

Globally, noroviruses are among the foremost causes of acute diarrheal disease, yet there are many unanswered questions on norovirus immunity, particularly following natural infection in young children during the first 2 years of life when the disease burden is highest. We conducted a literature review on birth cohort studies assessing norovirus infections in children from birth to early childhood. Data on infection, immunity, and risk factors are summarized from 10 community-based birth cohort studies conducted in low- and middle-income countries. Up to 90% of children experienced atleast one norovirus infection and up to 70% experienced norovirus-associated diarrhea, most often affecting children 6 months of age and older. Data from these studies help to fill critical knowledge gaps for vaccine development, yet study design and methodological differences limit comparison between studies, particularly for immunity and risk factors for disease. Considerations for conducting future birth cohort studies on norovirus are discussed.

Tropical and travel-associated norovirus: current concepts

PURPOSE OF REVIEW

We highlight recent advances relevant to understanding norovirus infections in the tropics, both in populations living in developing settings and travelers to these regions.

RECENT FINDINGS

Because of the decrease in diarrheal disease associated with the global rollout of vaccines against rotavirus, norovirus is emerging as the predominant cause of diarrhea morbidity among children in the tropics, and evidence suggests that it contributes to adult disease in endemic populations and travelers. In addition to identifying potential target populations for preventive measures, we provide an update on norovirus vaccine development and concepts related to their implementation in low-income and middle-income countries.

SUMMARY

These current concepts related to norovirus-attributable disease burden, clinical significance, and economic impact can potentially be applied to tailoring efforts to prevent and mitigate the effects of this important enteropathogen.

Complete nucleotide sequence analysis of the norovirus GII.17: A newly emerging and dominant variant in China, 2015

Norovirus is an important pathogen which accounts for majority of the viral related acute gastroenteritis. Recently, a variant of genotype GII.17 was reported to be predominant over GII.4 and accounted for several acute gastroenteritis outbreaks in Asia. In the current study, the full genome of a norovirus strain ZHITHC-12 isolated during this outbreak period in China was identified and characterized. The viral genome was 7557 nucleotides in length and a phylogenetic analysis based on full length genome sequences indicated that ZHITHC-12 belonged to GII.17 genotype. A further phylogenetic analysis based on all available polymerase and capsid sequences showed that ZHITHC-12 was in Cluster III on both phylogenetic trees and grouped with other strains also isolated during 2013 to 2015. Moreover, homology modeling analysis based on GII norovirus capsid 5BSX template revealed that substitutions, mutations, and more importantly, deletions and insertions, occurred at or near the putative epitopes and histo-blood group antigen (HBGA) binding sites in its protruding P2 domain, which might confer new antigenic or biological properties for this novel variant. In summary, the first full genome and capsid protein structure of a novel norovirus GII.17 variant isolated in China was extensively characterized. The data would be helpful not only for the epidemiology study, but also for the diagnostic tool development and effective vaccine design in the future.

Norovirus infections and seroprevalence of genotype GII.4-specific antibodies in a Spanish population

Genotype II.4 noroviruses (NoVs) are a leading cause of epidemic acute gastroenteritis in children and adults worldwide. The prevalence of different NoV genotypes causing outbreaks and sporadic cases of acute gastroenteritis in the region of Valencia, Spain, during a 4-year period (2008-11) was investigated. NoVs were detected in 42 out of 55 (76.3%) outbreaks and in 26 out of 332 (7.8%) sporadic cases of acute gastroenteritis. Genogroup GII strains were predominant in outbreaks and sporadic cases. Different genotype GII.4 variants were found (Yerseke_2006a, Den Haag_2006b, Apeldoorn_2007, and New Orleans_2009), with the latter variant detected most frequently (35.3%). A recombinant P domain of the NoV GII.4 Apeldoorn_2007 variant was produced in Escherichia coli and used as the coating antigen in an enzyme immunoassay to survey the IgG antibody seroprevalence against NoV GII.4 in a Spanish population. Baculovirus-expressed virus-like particles (VLPs) of NoV GII.4 Den Haag_2006b variant were also produced and used as antigen to compare seroreactivity. Of the 434 serum specimens analyzed, 429 (98.6%) had antibodies against the P domain. The comparison of reactivities of 30 serum samples to the NoV GII.4 P polypeptide and VLP showed reproducible results with a correlation coefficient of r = 0.794. Titers of antibodies to the P domain increased gradually and significantly with age, reaching the highest levels at the age group of 41-50 years. These results confirm the high prevalence of NoV GII.4 infections in Valencia from early childhood.

Noroviruses: epidemiology, immunity and prospects for prevention

In recent years, noroviruses have become recognized as an important cause of both sporadic and epidemic acute gastroenteritis (AGE), largely due to the improved availability of broadly reactive real-time RT-PCR (TaqMan-based RT-PCR) assays. While there is substantial diversity among noroviruses, one specific genotype, GII.4, is the most common etiology in sporadic and epidemic AGE. Outbreaks of norovirus AGE most commonly occur in healthcare facilities and restaurants and result in significant morbidity and mortality and substantial healthcare costs. Norovirus vaccine development is progressing, and Phase I and II human trials have shown proof-of-principle that norovirus vaccines can reduce illness and infection.

Gastrointestinal pathogens detected by multiplex nucleic acid amplification testing in stools of pediatric patients and patients returning from the tropics

BACKGROUND

Gastrointestinal infections are caused by a broad spectrum of pathogens. Conventional diagnostic procedures are resource and time consuming due to single pathogen testing, often in different laboratories.

METHOD

We analyzed 312 consecutive stool samples from pediatric patients (n = 127) with gastroenteritis or from adult travelers returning from the tropics with suspected parasite infestation (n = 185) using commercial multiplex nucleic acid amplification testing (NAT) (xTAG gastrointestinal pathogen panel, Luminex) covering 15 diarrhea-causing pathogens. The results of the positive samples and a representative number of negative samples were compared to standard methods, including NAT, direct antigen detection (DAD), bacterial culture and microscopy.

RESULTS

Of the 185 samples from adult travelers, 21 (11 %) were multiplexNAT-positive, with enterotoxigenic Escherichia coli (4 %) being the predominant pathogen. Microscopic examination revealed Blastocystis hominis in 23 % not covered by the panel. MultiplexNAT scored positive in 66 pediatric samples (52 %), with rotavirus (27 %) being the most prevalent. All adenovirus-, rotavirus-, Clostridium difficile- and Cryptosporidium-positive samples were confirmed in external laboratories, but only 40 % of norovirus- and 29 % of Giardia-positive samples. Analysis of frozen specimens by bacterial culture showed the highest discrepancies with the multiplexNAT.

CONCLUSION

Our study demonstrates broad detection of relevant gastroenteritis pathogens by multiplexNAT with a short turnaround time. This is important for diagnosis, infection control and empiric management of gastroenteritis patients, but may be selectively complemented by bacterial culture and resistance testing.

Molecular epidemiology of rotavirus and norovirus in Ile-Ife, Nigeria: high prevalence of G12P[8] rotavirus strains and detection of a rare norovirus genotype

Rotavirus (RV) and norovirus (NoV) are considered the most common causes of viral gastroenteritis in children. In this study, the prevalence of RV and NoV infection in 55 children with diarrhea from the rural community Akinlalu in Southwestern Nigeria was investigated using real-time PCR assays. The RV and NoV strains were genotyped by PCR and/or sequencing. RV and NoV infections occurred with a prevalence of 34.5% and 25.5% respectively, with predominance in children <1 year. Most infections occurred during the dry season with increasing prevalence of RV as the dry season progressed (October-January). Infections with RV VP6 subgroup (SG) II were more prevalent (27.3%) than SGI (7.3%). Similarly, NoV genogroup II infections were more common (23.6%) than genogroup I (1.8%). Five children out of 55 (9.1%) were co-infected with both RV and NoV. Notably, G12P[8] was the predominant RV strain (36.8%, n = 7), observed for the first time in Nigeria. The VP7 gene of the G12 strains clustered within lineage III, sharing high nucleotide identity with each other (>99%) indicating introduction in Nigeria from a single donor. Furthermore, a putative novel genotype within genogroup I NoV was detected, which till date has only been reported once in humans. To conclude, a high prevalence of the emerging G12P[8] RV strain was observed for the first time in Nigeria, as well as a putative novel NoV genotype in humans. These results provide new information which can be important for future vaccine evaluations and possible introduction in Nigeria.

Predicting susceptibility to norovirus GII.4 by use of a challenge model involving humans

BACKGROUND

GII.4 is the predominant norovirus genotype worldwide. Challenge models involving humans have shown the association of human histo-blood group antigens (HBGAs) and susceptibility to infection with Norwalk virus (GI.1 norovirus), but the association of HBGAs and infection with other noroviruses is based on results of epidemiological studies. We performed the first GII.4 challenge study involving humans and prospectively evaluated the relationship between HBGAs and norovirus infection and associated illness.

METHODS

Forty healthy adults (23 secretors and 17 nonsecretors of HBGAs) were challenged with 5 10(4) reverse-transcription polymerase chain reaction (RT-PCR) units of GII.4 norovirus. Subjects were assessed daily for clinical illness, and stool specimens were evaluated for norovirus by RT-PCR. Infection was defined by detection of norovirus and/or seroconversion to GII.4 antibody.

RESULTS

Of the 23 secretors, 16 (70%) were infected with norovirus, 13 (57%) became ill (characterized by vomiting and/or diarrhea), and 12 (52%) developed norovirus-associated illness. In contrast, only 1 nonsecretor (5.9%) became ill, and another nonsecretor shed virus for a single day (P < .001 for each variable, compared with secretors). Infection occurred in secretors regardless of ABO blood group. Illness was mild to moderate in severity and lasted 1-3 days.

CONCLUSIONS

Secretor status determined the susceptibility to norovirus GII.4 challenge. This human challenge model should be useful for evaluating norovirus vaccines and antiviral agents. Clinical trials registration. NCT01322503.

Molecular detection of murine noroviruses in laboratory and wild mice

Fecal specimens collected from 121 laboratory mice, 30 striped field mice (Apodemus agrarius), 70 yellow-necked mice (Apodemus flavicollis), and 3 bank voles (Myodes glareolus) were tested in sample pools for the presence of murine noroviruses (MNV). Ten of 41 laboratory mice and 2 of 3 striped field mice pooled samples were positive for MNV. All laboratory mouse MNVs were closely related to previously described MNVs. The complete ORF2 (VP1) of both striped field mouse MNVs identified in this study was 1623 nt (541 aa) long and differed at 12% nt (8% aa) positions from each other, at 22-24% nt (15-18% aa) positions from the laboratory mouse MNVs and at 20-22% nt (13-14% aa) positions from the recently described wood mouse (Apodemus sylvaticus) MNVs. This study provides further evidence for the circulation of novel, genetically diverse MNVs in wild mice.

Molecular characterization of human calicivirus associated with acute diarrheal disease in Mexican children

Background

Human caliciviruses (HuCV) are emerging enteric pathogens that are a common cause of diarrhea in humans worldwide. Due to the paucity of information on the molecular characterization of HuCV circulating in Mexico, the aim of this work was to investigate the diversity and molecular epidemiology of the HuCV infection associated with acute diarrheal disease in Mexican children aged up to 5 years.

Results

Of the 131/414 (32%) HuCV positive-specimens analyzed, 128 were identified as Norovirus (NoV) and three as Sapovirus (SaV). Of the NoV positive specimens, 118/128 (92%) were NoV GII and 10/128(8%) were untypeable by RT-PCR in both polymerase and capsid genes, whereas one SaV isolate was further confirmed by sequencing as GI.2. Phylogenetic analysis based on polymerase partial gene sequences from 89/131 (68%) HuCV isolates showed that 86/89 (97%) belong to NoV GII.4 with three main variant clusters of this genotype, 2/89 (2%) to NoV GII.2, and 1/89 (1%) to SaV GI.2. Furthermore, partial sequencing of the capsid gene VP1 of 63/131 (48%) strains indicated that 61/63 (97%) correlated with NoV GII.4, whereas only 2/63 (3%) clustered to NoV GII.2. HuCV infections were detected throughout the year, and the highest number of cases positive for NoV was found in children between 7 and 18 months of age (60%).

Conclusions

This study highlights the usefulness of analyzing both polymerase and capsid genes for molecular characterization of HuCV and demonstrates the relatedness and predominance of NoV GII.4 with acute diarrheal disease in young Mexican children, thus contributing to better understanding of the molecular epidemiology of this disease.

Pediatric norovirus diarrhea in Nicaragua

Information about norovirus (NoV) infections in Central America is limited. Through a passive community and hospital pediatric diarrhea surveillance program, a total of 542 stool samples were collected between March 2005 and February 2006 in León, Nicaragua. NoV was detected in 12% (65/542) of the children; of these, 11% (45/409) were in the community and 15% (20/133) were in the hospital, with most strains (88%) belonging to genogroup II. NoV infections were age and gender associated, with children of <2 years of age (P < 0.05) and girls (P < 0.05) being most affected. Breast-feeding did not reduce the number of NoV infections. An important proportion (57%) of NoV-infected children were coinfected with diarrheagenic Escherichia coli. A significant proportion (18/31) of NoV-positive children with dehydration required intravenous rehydration. Nucleotide sequence analysis (38/65) of the N-terminal and shell region in the capsid gene revealed that at least six genotypes (GI.4, GII.2, GII.4, GII.7, GII.17, and a potentially novel cluster termed "GII.18-Nica") circulated during the study period, with GII.4 virus being predominant (26/38). The majority (20/26) of those GII.4 strains shared high nucleotide homology (99%) with the globally emerging Hunter strain. The mean viral load was approximately 15-fold higher in children infected with GII.4 virus than in those infected with other G.II viruses, with the highest viral load observed for the group of children infected with GII.4 and requiring intravenous rehydration. This study, the first of its type from a Central American country, suggests that NoV is an important etiological agent of acute diarrhea among children of <2 years of age in Nicaragua.

Genetic relatedness of noroviruses identified in sporadic gastroenteritis in children and gastroenteritis outbreaks in northern Alberta

We compared the proportion and genotype distribution of norovirus (NoV) identified in sporadic acute gastroenteritis in children younger than 7 years old with the NoV strains found in outbreaks from January 2003 through April 2004 in northern Alberta, Canada. Eight genogroup I (GI) and 133 GII NoV cases were detected in 1,166 cases of acute sporadic childhood gastroenteritis with a monthly detection rates varying from 6.0% to 20.4% and no sporadic gastroenteritis case in October 2003. Seventy-eight outbreaks (65%) tested positive for NoV during the study period with an obvious winter predominance and no NoV outbreaks in August, September, and October 2003. Three GI and 51 GII strains from the sporadic childhood gastroenteritis cases and seven GI and 37 GII strains from gastroenteritis outbreaks were sequenced and analyzed. Strains belonging to the GII.4 cluster predominated in outbreaks (68%) while the strains in sporadic childhood gastroenteritis demonstrated significant heterogeneity with the majority belonging to the GII.3 cluster (36%). Further analysis of NoV strains from 34 sporadic childhood gastroenteritis cases and 38 gastroenteritis outbreaks in chronologically and geographically related groups failed to demonstrate clear link between strains circulating in the setting of sporadic childhood gastroenteritis and those found in outbreaks.

Molecular epidemiology of norovirus infections in children with acute gastroenteritis in South Korea in November 2005 through November 2006

Norovirus infections were detected in 114 of 762 children with acute gastroenteritis in South Korea from November 2005 to November 2006. Seasonality peaks in December, March, and October were also assessed in this study. We identified seven noroviral genotypes (GI-6, GII-2, GII-3, GII-4, GII-5, GII-6, and GII-8) and a C1-120 strain showing low identity (79.3%) with GII-13 and GII-17.

Real-time reverse transcription PCR detection of norovirus, sapovirus and astrovirus as causative agents of acute viral gastroenteritis

The design and development of highly sensitive real-time reverse transcription PCR assays for the detection of norovirus genogroups I, II and IV, sapovirus genogroups I, II and IV, and human astrovirus from stool samples is described. Examination of 140 stool samples from paediatric patients exhibiting symptoms of diarrhoea and/or vomiting resulted in increased detection levels as compared to examination by electron microscopy. Real-time PCR resulted in a 200% increase in the rate of detection of norovirus as compared to electron microscopy. Only genogroup II noroviruses were detected in the stool specimens and when examined using partial-genotyping primers all were identified as clustering with the genogroup II/4(Bristol/Lordsdale) cluster. Sapovirus was not detected in any of the stool specimens by electron microscopy while 11% (15/140) of specimens were sapovirus positive by real-time RT-PCR, accounting for 36% of calicivirus diarrhoea. Real-time RT-PCR resulted in a tenfold increase in the rate of detection of astrovirus when compared to detection by electron microscopy with both type 1 and type 4 human astroviruses being detected in circulation. The results highlight the importance of the introduction of molecular methods for the routine screening of stool samples for causative agents of viral gastroenteritis.

Molecular and epidemiological trend of norovirus associated gastroenteritis in Dhaka City, Bangladesh

BACKGROUND

Diarrhea, over the years, has killed millions of people and continues to be a major threat in Bangladesh.

OBJECTIVES

To determine the incidence of norovirus infection in infants and young children with acute gastroenteritis in Dhaka City, Bangladesh and to determine the genogroup and genotype in norovirus-positive stool specimens.

STUDY DESIGN

Fecal specimens were collected from infants and children with acute gastroenteritis in Dhaka City, Bangladesh from October 2004 to September 2005, and examined for norovirus by reverse transcription-polymerase chain reaction.

RESULTS

Noroviruses were detected in 41 of 917 fecal specimens. Molecular analysis of norovirus was carried out by sequencing methods. Only norovirus GII/4 strains were detected during this study. The dominant genotype throughout the study period was GII/4. Norovirus infections were most commonly observed in winter and rainy seasons in Dhaka City. The common clinical symptoms in norovirus-infected patients were diarrhea (90%), vomiting (75%) and abdominal pain (46%).

CONCLUSIONS

This is the first epidemiological research of norovirus in Bangladesh. Norovirus is an important enteropathogen responsible for viral gastroenteritis among infants and children in Bangladesh.

Human sapoviruses: genetic diversity, recombination, and classification

The family Caliciviridae contains four genera Sapovirus, Norovirus, Lagovirus and Vesivirus, which include Sapporo virus (SaV), Norwalk virus (NoV), Rabbit hemorrhagic disease virus (RHDV) and Feline calicivirus (FCV), respectively. SaV is a causative agent of gastroenteritis in children and adults. SaV can be divided into five genogroups (GI-GV), among which GI, GII, GIV and GV are known to infect humans, whereas SaV GIII infects porcine species. Detection methods include ELISA, RT-PCR and real-time RT-PCR. Since few SaV studies have been conducted, it is difficult to draw correlations between or conclusions about rates of incidence, detection and overall prevalence. Nevertheless, most studies agree that SaV infection is more frequent in young children than adults and that infection in children almost always occurs by 5 years of age. In addition, children at day-care centres and institutions are at greatest risk of SaV-associated infection and transmission. Recently, a number of important findings concerning human SaV were discovered. SaV strains were detected in water samples, which included untreated wastewater specimens, treated wastewater samples and river samples. SaV strains were also detected in shellfish samples destined for human consumption, and recombinant SaV strains were identified in a number of different countries. The purpose of this review was to highlight the current knowledge of human SaV, which appears to be an increasingly important virus causing gastroenteritis in humans.

Norovirus mixed infection in an oyster-associated outbreak: an opportunity for recombination

We describe an outbreak of gastroenteritis in which the nucleic acid of three distinct noroviruses was amplified from the same fecal sample. To enable the separate amplification of each virus, an inclusion/exclusion RT-PCR primer design strategy was developed. This paired a virus-specific exclusion primer (designed with the exact sequence of one virus in a region displaying low conservation among the three viruses) with a virus-nonspecific inclusion primer (designed in a conserved region). Thus, in each reaction the exclusion primer provided specificity for a single virus, and the inclusion primer increased the sensitivity and allowed hybridization in a region of unknown sequence. Analysis of the partial genomic sequences of the three viruses (3.6-3.8 kb) indicated that each virus belonged to a separate genogroup II cluster, and each displayed evidence of a potential recombination event when the sequences were compared with other published norovirus sequences. Our results, which show a mixed norovirus infection in a single individual, confirm the need to be aware of the possibility of mixed norovirus infections, and of the possibility of genomic recombination causing anomalies in phylogenetic analyses in such instances.

Development of an enzyme immunoassay for detection of sapovirus-specific antibodies and its application in a study of seroprevalence in children

Sapoviruses (SVs) are an important cause of acute pediatric gastroenteritis. Due to the lack of appropriate diagnostic methods, the epidemiology of SV-associated illness remains poorly understood. Baculovirus and Escherichia coli expression systems were evaluated for the development of antibody detection enzyme immunoassays (EIA). Age-related antibody prevalence in children was studied using the new EIA. Because of the low yield of the baculovirus system, the E. coli-expressed SV capsid proteins were used to develop the EIA. The antigenic specificities of the E. coli-expressed SV capsid proteins were demonstrated using hyperimmune antisera raised in animals and sera collected from patients. A high prevalence (>90%) of antibodies to both SV (strain Mex340) and norovirus (strain VA387) was observed in children involved in a birth cohort at 20 to 24 months of age; however, at 1 to 3 months of age, <25% of the children possessed anti-SV antibodies versus >90% with anti-NV antibodies. The E. coli-derived SV proteins are an excellent source of antigens for the EIA. SV infection is common in the first 2 years of life. The low prevalence of maternal antibodies detected in Mexican children against SVs in this study is unique and needs to be addressed in future studies.

Asymptomatic norovirus infection in Mexican children

Sixty-three children in periurban Mexico City were examined for the occurrence of asymptomatic norovirus (NoV) infection from June to August 1998. NoV was detected in 48 of 161 stool specimens (29.8%), with 31 children (49.2%) having at least one positive stool. Asymptomatic NoV infection occurred commonly during summertime in a Mexican pediatric population.

Genetic diversity of norovirus among children with gastroenteritis in São Paulo State, Brazil

Norovirus (NoV) is one of the most common causes of acute gastroenteritis in children and adults. To study the prevalence and genetic variability of NoV in children with acute gastroenteritis in São Paulo State, Brazil, we examined 234 stool samples from children with or without gastroenteritis during a 5-year period (1995 to 1999). NoV RNA was detected by reverse transcription-PCR and confirmed by DNA sequence analysis. We used two different oligonucleotide primer sets targeting the 3' end of the RNA polymerase gene (region B), as well a partial capsid region at the 3' end of the VP1 gene (region D). A total of 78 (33.3%) of the samples tested positive for NoV, and in region B, of the 66 strains sequenced, 4 (6.1%) belonged to GI, 52 (78.7%) belonged to GII, and five samples (7.6%) contained a mixture of the GI and GII genotypes. Phylogenetic analysis showed that the majority (40 of 66 [60.6%]) of the strains belonged to genotype GII.4. The nucleotide sequence identity of three strains was lower than 77.9% compared to a region B reference sequence database but showed 85.3 to 88.8% identity with GII.2 Melksham strain in region D, indicating the circulation of a possible recombinant NoV strain. One sample (GII.3) was sequenced only in region D. In conclusion, we have a total of 67 sequenced strains. This is the first report that describes the predominance of GII.4 NoV strains in children visiting the ambulatory of different hospitals in São Paulo State, Brazil, and we show that mixtures of different strains can be found in individual samples, including some possible new recombinant strains.

Detection of calicivirus from fecal samples from children with acute gastroenteritis in the West Central region of Brazil

The objective of this study was to describe the circulation of caliciviruses in the West Central region of Brazil and its correlation with children's gender and age, as well as with the year and months of the sample collection. Reverse transcriptase-polymerase chain reaction was performed to detect the human calicivirus genome in 1006 fecal samples that were collected in Goiânia (n = 696) and Brasília (n = 310). Viral RNA was detected in 8.6% of the samples. No significant difference in viral prevalence was found regarding gender, age or year of the sample. However, it was observed that in Goiânia, there is a higher incidence of caliciviruses from September to March. The analysis employing three primer pairs demonstrated that the Ni/E3 or JV12/13 primer pairs, which detect norovirus (NoV), detected 41 positive samples while the 289/290 primer pair, which detects NoV or sapovirus, detected the remaining 46 samples. Calicivirus circulates in the West Central region of Brazil and for better detection of this virus it is important to use more than one primer pair. Also, we conclude that the seasonality presented by this virus is related to higher humidity in the period.

Molecular detection of porcine enteric caliciviruses in Venezuelan farms

Caliciviruses are a well-established cause of respiratory, vesicular and hemorrhagic diseases in animals. In addition, these viruses are an important cause of enteric diseases in humans. Recently, molecular analysis of several porcine enteric caliciviruses indicated that they are closely related to human enteric caliciviruses. The objective of this work was to determine the frequency, age distribution, and association with diarrhea of enteric calicivirus infections in piglets and to partially characterize the detected isolates. A total of 203 stool samples from animals 0 to 9 weeks of age, collected between 1993 and 2003 in seven porcine farms located in the central region of Venezuela were tested for enteric caliciviruses by reverse transcription-polymerase chain reaction (RT-PCR) amplification using primers designed to detect both norovirus and sapovirus. Selected amplicons were sequenced to establish phylogenetic relationships with reference strains. Calicivirus were detected in 18% (36/204) of the samples. Viruses were detected more frequently in animals between 3 and 4 weeks of age, and were detected in samples from animals with diarrhea and without diarrhea with equal frequencies (14 versus 19%, p>0.5). Phylogenetic studies based on partial RNA polymerase gene sequences indicated that the Venezuelan isolates were most closely related (75-95% identity) to the sapovirus Cowden reference strain. These results provide evidence that caliciviruses of the genus sapovirus circulate frequently in piglets but further studies are needed to clarify their importance as cause of diarrhea.

Multiple viral infections and genomic divergence among noroviruses during an outbreak of acute gastroenteritis

An epidemic outbreak of both norovirus (NV) and astrovirus (ASV) occurred on a research ship surveying Tokyo Bay, causing acute gastroenteritis in 26 of its 37 crew members. The presence of viral pathogens in fecal specimens was analyzed, and noroviruses were identified by reverse transcription-PCR in 18 (48.6%) of these specimens. In addition, astroviruses were identified in 14 (37.8%) of the fecal samples from the affected crew members, and multiple viral infections of both NV and ASV were observed in 6 cases. The genogrouping of the NV-positive samples was then examined by dot blot hybridization, and it was determined that all of the isolates were from genogroup II (GII). No bacterial pathogens were subsequently isolated from fecal specimens. Furthermore, a variety of NV strains were identified by sequencing and single-stranded conformational polymorphism (SSCP) analyses of PCR products from the fecal samples. One recombinant NV isolate, Minato/14, was identified as a recombinant NV strain of GII/6 and GII/1. The other NV isolates from this outbreak were classified into three NV genotypes (GII/1 [Minato/10], GII/4 [Minato/33], and GII/5 [Minato/6]). Furthermore, ASVs in positive samples were determined to belong to serotypes 1 and 2 by sequencing analysis. Our findings thus indicate that coinfections with NV and ASV, including a number of NV genotypes, persisted during an outbreak of gastroenteritis in a closed environment.

Genetic analysis of calicivirus genomes detected in intestinal contents of piglets in Japan

Enteric caliciviruses, noroviruses, and sapoviruses are emerging pathogens responsible for diarrhea or gastroenteritis in their respective hosts. In this study, swine enteric caliciviruses were detected in ten samples of intestinal contents from 24 piglets in Japan by reverse transcription-polymerase chain reaction using a broadly reactive primer pair (P290/289) that targeted the highly conserved RNA polymerase regions of the enteric caliciviruses. From the positive samples, the entire viral genome of strain K7/JP and 3'-end parts of the genomes of strains K5/JP and K10/JP were cloned and sequenced. K7/JP had an RNA genome of 7144 bases, excluding its 3' poly (A) tail. The K7/JP genome possessed two open reading frames and characteristics common to sapoviruses. In phylogenetic analysis using amino acid sequences of VP1, K5/JP was demonstrated to be close to the noroviruses previously detected in pigs, and K7/JP and K10/JP were considered to be classified as a new genogroup of sapoviruses.

Molecular epidemiology of caliciviruses detected in sporadic and outbreak cases of gastroenteritis in France from December 1998 to February 2004

We compiled sequence and epidemiological data from 172 caliciviruses detected in France from December 1998 to February 2004 in sporadic and outbreak cases. The results showed a cocirculation of strains with a majority of genogroup II (GII) noroviruses. Three groups of noroviruses, not detected before in our laboratory, emerged and spread during the period: the recombinant GGIIb and Norwalk-related strains not amplified in the polymerase gene in 2000 and a new Lordsdale variant in 2002. We observed that (i) GII-4 noroviruses were predominant in nursing home and hospital outbreaks but rare in oyster- and water-related outbreaks despite continuous circulation in the population; (ii) at the opposite, genogroup I strains were detected in the majority of environmental outbreaks; (iii) several strains were frequently found in oyster- and water-linked outbreaks (up to seven), whereas one single strain was detected when transmission was from person to person; and (iv) whereas GII noroviruses were predominant in sporadic cases where patients were under 15 years of age, GI strains were more frequent in outbreaks occurring in this age group. Finally, from a methodology point of view, this compilation shows that detection and characterization in the polymerase gene are not adequate in a significant number of cases and should be completed by amplification and sequencing in the capsid gene.

Seroprevalence of noroviruses in swine

Noroviruses (NVs) are important human pathogens that cause acute gastroenteritis. Genetically related animal enteric NVs have also been described, but there is no evidence of interspecies transmission of NVs. In this study we characterized antibody prevalence among domestic pigs by using recombinant capsid antigens of two human NVs (Norwalk and Hawaii) and one swine NV (SW918) that is genetically related to GII human NVs. Recombinant SW918 capsid protein expressed in baculovirus self-assembled into virus-like particles (VLPs) that were detected by antibodies against GII (Hawaii and Mexico), but not GI (Norwalk and VA115), human NVs. NVs recognize human histo-blood group antigens as receptors, but SW918 VLPs did not bind to human saliva samples with major histo-blood group types. Seventy-eight of 110 (71%) pig serum samples from the United States and 95 of 266 (36%) pig serum samples from Japan possessed antibodies against SW918. Serum samples from pigs in the United States were also tested for antibodies against human NVs; 63% were positive for Norwalk virus (GI) and 52% for Hawaii virus (GII). These results indicate that NV infections are common among domestic pigs; the finding of antigenic relationships between SW918 and human NVs and the detection of antibodies against both GI and GII human NVs in domestic animals highlights the importance of further studies on NV gastroenteritis as a possible zoonotic disease.

Calicivirus infection in human immunodeficiency virus seropositive children and adults

BACKGROUND

The importance of enteric viral infections in HIV-related diarrhea is uncertain. Human caliciviruses have emerged as a leading cause of acute diarrhea worldwide.

OBJECTIVES

To evaluate the importance of calicivirus infections in HIV-related diarrhea. Study design 151 fecal samples collected from children and adults infected with HIV, with and without diarrhea, were examined. In addition, 89 fecal samples from non HIV-infected children and adults were also tested. Samples were analyzed by RT-PCR using primer sets specific to Norovirus genogroup I or genogroup II as well as primers designed to react with both Noroviruses and Sapovirus genus.

RESULTS

Viruses were detected with equal frequencies in stools from HIV infected and non-infected adults (12%). However, specimens from HIV infected children were more likely than those of HIV-negative children to have caliciviruses (51% versus 24%, P<0.05). Viral infections were not significantly associated with diarrhea neither in children nor in adults, regardless of HIV status. Viruses genetically related to the common Lordsdale virus (Norovirus genogroup II) and London/92 virus (Sapovirus) clusters were detected circulating among children.

CONCLUSIONS

These results suggest that caliciviruses may be an important opportunistic pathogen in children infected with HIV.

Molecular epidemiology of norovirus infections in Stockholm, Sweden, during the years 2000 to 2003: association of the GGIIb genetic cluster with infection in children

The incidence of norovirus-associated gastroenteritis and the molecular epidemiology of norovirus strains were studied during three seasons (2000-2001, 2001-2002, and 2002-2003) among patients of all ages, mainly from the Stockholm region in Sweden. A total of 3,252 fecal samples were analyzed by reverse transcription-PCR. The incidences of norovirus infection among adults were 23, 26, and 30% during the three seasons studied and 18, 11, and 15% among children 0 to 15 years of age. During the first season, all norovirus strains detected by PCR were typed either by reverse line blot hybridization or nucleotide sequence analysis. During the two successive seasons, a total of 60 norovirus-positive strains from the beginning, peak, and end of the seasons were selected for nucleotide sequence analysis. We identified two dominant norovirus variants over the seasons: a new norovirus variant, recently described as the GGIIb genetic cluster, dominated among children during the first season, and during the following two seasons, a GGII-4 variant dominated. Our data suggest that norovirus infections are common, not only among adults, but also among children, and that some strains may predominantly affect children.

Detection and characterization of human caliciviruses in hospitalized children with acute gastroenteritis in Blantyre, Malawi

The human caliciviruses (HuCVs), including Norovirus and Sapovirus, are recognized causes of acute gastroenteritis in children and adults. A 1-year study was undertaken in Blantyre, Malawi, to examine the prevalence, and genetic diversity, of human caliciviruses (HuCVs) amongst children under 5 years of age hospitalized with acute gastroenteritis. Using the reverse transcription-polymerase chain reaction (RT-PCR), combined with nucleotide sequencing of the RT-PCR products, HuCVs were detected in 34/398 (8.5%) of children. Twelve (35.3%) of the children were co-infected with additional enteric viruses (predominantly rotavirus). The HuCVs comprised 26 Noroviruses (6.5%) and 8 Sapoviruses (2.0%). Each of the Noroviruses belonged to genogroup II, and could be further classified into six genotypes, including GII/3 (18 strains), GII/4 (2 strains), GII/11 (1 strain), GII/13 (1 strain), GII/16 (2 strains), and a putative new genotype GII/20 (2 strains). Each of the Sapoviruses belonged to genogroup GIII. HuCVs are the second most commonly identified viral enteropathogens (after rotavirus) among hospitalized children with gastroenteritis in Malawi.

Seroprevalence of antibodies against noroviruses among students in a Chinese military medical university

Noroviruses (NVs) are important causes of nonbacterial gastroenteritis in humans, but the role of NVs as a cause of diseases in the Chinese people, particularly in Chinese military personnel, remains unclear. This study investigated antibody prevalence and factors that associate with the prevalence of antibody to NVs among students attending a military medical university. Serum specimens were tested by an enzyme-linked immunosorbent assay for immunoglobulin G antibody to recombinant capsid antigens of three NVs (rNorwalk, rMxV, and rVA387). Of 588 serum samples tested, the antibody prevalence was 88.9, 54.1, or 90.0% for the three antigens, respectively. There were significant differences in the prevalence of antibody to rMxV between blood types (P < 0.05); the prevalence for type O was the highest (62.5%), and the prevalence for type B was the lowest (49.1%). The average optical density values for antibody to rNorwalk and rMxV were lowest among students with type B. The number of students who did not have antibody to any of the three antigens was the highest for blood type B (6.9%) compared to other blood types (0.8 to 3.4% [P < 0.006]). The antibody prevalence also varied with the hometown residencies of the students before joining the military, with the highest rates for students from rural areas, lower rates for students from small towns or villages, and the lowest rates for students from large cities. The numbers of students who did not have antibody to any of the three antigens were highest for students from the large cities, lower for students from small towns or villages, and lowest for students from rural areas. The distribution of ABO blood types did not differ among the three groups. These data suggest that NVs are prevalent in China and that both genetic and environmental factors play a role in NV infection.

Diversity of enteric viruses detected in patients with gastroenteritis in a tertiary referral paediatric hospital

The genetic diversity of enteric viruses co-circulating in a cohort of patients with viral gastroenteritis in a large tertiary paediatric hospital in London, UK, was determined. Multiple strains of noroviruses (NV), sapoviruses (SV) and astroviruses (HAsV) were detected in these patients, indicating the likelihood of multiple introductions from different sources, possible sub-clinical infections and simultaneous infection with different viruses in immunocompromised and other patients. Routine screening of immunocompromised patients and infection control procedures are important to prevent nosocomial infection.

Human caliciviruses and pediatric gastroenteritis

Surveillance using molecular diagnostic methods developed in the past decade shows that human caliciviruses, particularly the Noroviruses, are the most important cause of pediatric acute gastroenteritis, next to rotavirus. Noroviruses also cause severe gastroenteritis in children, requiring hospitalization. The Sapovirus, a morphologically and genetically distinct genus of calicivirus, cause mainly milder endemic pediatric gastroenteritis. Noroviruses and Sapoviruses are genetically and antigenetically diverse, and multiple genetic types cocirculate in the same community. Human caliciviruses still cannot be cultivated in cell culture or in an animal model. Significant progress has been made in the past decade in the classification, diagnosis, and vaccine development, as well as in the recent discovery of Norovirus recognizing human histoblood group antigens as receptors. Major developments in this field are expected to occur in the near future.

Human milk oligosaccharides are associated with protection against diarrhea in breast-fed infants

OBJECTIVE

To determine the association between maternal milk levels of 2-linked fucosylated oligosaccharide and prevention of diarrhea as a result of Campylobacter, caliciviruses, and diarrhea of all causes in breast-fed infants.

STUDY DESIGN

Data and banked samples were analyzed from 93 breast-feeding mother-infant pairs who were prospectively studied during 1988-1991 from birth to 2 years with infant feeding and diarrhea data collected weekly; diarrhea was diagnosed by a study physician. Milk samples obtained 1 to 5 weeks postpartum were analyzed for oligosaccharide content. Data were analyzed by Poisson regression.

RESULTS

Total 2-linked fucosyloligosaccharide in maternal milk ranged from 0.8 to 20.8 mmol/L (50%-92% of milk oligosaccharide). Moderate-to-severe diarrhea of all causes (n=77 cases) occurred less often (P=.001) in infants whose milk contained high levels of total 2-linked fucosyloligosaccharide as a percent of milk oligosaccharide. Campylobacter diarrhea (n=31 cases) occurred less often (P=.004) in infants whose mother's milk contained high levels of 2'-FL, a specific 2-linked fucosyloligosaccharide, and calicivirus diarrhea (n=16 cases) occurred less often (P=.012) in infants whose mother's milk contained high levels of lacto-N-difucohexaose (LDFH-I), another 2-linked fucosyloligosaccharide.

CONCLUSION

This study provides novel evidence suggesting that human milk oligosaccharides are clinically relevant to protection against infant diarrhea.

A simple and rapid single-step multiplex RT-PCR to detect Norovirus, Astrovirus and Adenovirus in clinical stool samples

A single-step multiplex reverse transcription-polymerase chain reaction (RT-PCR) assay that detects and identifies Norovirus, Astrovirus and Adenovirus in clinical stool samples is described. Four hundred sixty stool samples were tested from patients with non-rotavirus acute gastroenteritis, that were either stored at -80 degrees C and tested retrospectively, or tested immediately after viral nucleic acid extraction in a prospective manner, including outbreaks of gastroenteritis that occurred in Germany during the winter of 2003. The multiplex RT-PCR was validated against simplex RT-PCR with published primers for Norovirus (JV12/JV13 and p289/p290) and Astrovirus (Mon340/348), and against simplex PCR for Adenovirus. In both retrospective and prospective settings, the multiplex RT-PCR was equally sensitive and specific in detecting non-rotavirus infections compared with simplex RT-PCR/PCR. The specificity of the multiplex RT-PCR was assessed by sequencing of the amplicons that showed high nucleotide identities to Norovirus genogroup I/1, I/4, II/2, or II/4 clades, as well as to Astrovirus serotypes 1, 2, 4, or 8. The multiplex RT-PCR was also more sensitive than Astrovirus and Norovirus antigen enzyme immunoassays (IDEIA, Dako), as well as Astrovirus isolation in cell culture. This novel multiplex RT-PCR is an attractive technique for the rapid, specific, and cost-effective laboratory diagnosis of non-rotavirus acute gastroenteritis.

Genetic diversity of norovirus and sapovirus in hospitalized infants with sporadic cases of acute gastroenteritis in Chiang Mai, Thailand

Stool specimens from hospitalized infants with sporadic gastroenteritis in Chiang Mai, Thailand, between July 2000 and July 2001 were examined for norovirus and sapovirus by reverse transcription-PCR and sequence analysis. These viruses were identified in 13 of 105 (12%) specimens. One strain was found to be a recombinant norovirus.

Noroviruses associated with acute gastroenteritis in a children's day care facility in Rio de Janeiro, Brazil

Noroviruses (Norwalk-like viruses) are an important cause of gastroenteritis worldwide. They are the most common cause of outbreaks of gastroenteritis in the adult population and occur in nursing homes for the elderly, geriatric wards, medical wards, and in hotel and restaurant settings. Food-borne outbreaks have also occurred following consumption of contaminated oysters. This study describes the application of a reverse transcription-polymerase chain reaction (RT-PCR) assay using random primers (PdN6) and specific Ni and E3 primers, directed at a small region of the RNA-dependent RNA polymerase-coding region of the norovirus genome, and DNA sequencing for the detection and preliminary characterisation of noroviruses in outbreaks of gastroenteritis in children in Brazil. The outbreak samples were collected from children <5 years of age at the Bertha Lutz children's day care facility at Oswaldo Cruz Foundation (Fiocruz), Rio de Janeiro, that occurred between 1996 and 1998, where no pathogen had been identified. At the Bertha Lutz day care center facility, only Fiocruz's employee children are provided for, and they come from different social, economic and cultural backgrounds. Three distinct genogroup II strains were detected in three outbreaks in 1997/98 and were most closely related to genotypes GII-3 (Mexico virus) and GII-4 (Grimsby virus), both of which have been detected in paediatric and adult outbreaks of gastroenteritis worldwide.

Incidence and characteristics of endemic Norwalk-like virus-associated gastroenteritis

Endemic gastroenteritis associated with the Norwalk-like viruses (NLVs) is little understood. This study tested for NLV in gastroenteritis cases in 257 households in Melbourne, Australia, for the period September 1997 to February 1999 by a reverse transcription hemi-nested polymerase chain reaction. Positive samples were studied by nucleotide sequencing and phylogenetic analysis. NLV was detected in 73 (11.4%) of 638 faecal specimens tested. Twelve (1.9%) were NLV genogroup 1 (G1) and 61 (9.6%) NLV genogroup 2 (G2). Gastroenteritis symptoms associated with NLV G2/no other pathogens were significantly more severe than where no NLV was detected. NLV G1 and NLV G2 were detected in adults and children, males and females. NLV G2 incidence showed a marked seasonal periodicity with significant peaks in the Australian late spring/early summer periods. NLV G1 seasonality was significantly different from that of NLV G2. Seven major NLV clusters were identified by phylogenetic analysis.

Molecular detection of human calicivirus among Spanish children with acute gastroenteritis

A survey was conducted among Spanish children with gastroenteritis treated in an emergency room. Reverse transcription-PCR with specimens negative for other enteric pathogens was used. The minimum incidence of human calicivirus infection was 7.7%, with Lordsdale as the predominant genotype. The clinical features and severity of calicivirus and rotavirus were similar.

Molecular detection and sequence analysis of human caliciviruses from acute gastroenteritis outbreaks in Hungary

Three viral gastroenteritis (VGE) outbreaks that occurred in 1998-1999, in Hungary were investigated for the presence of human caliciviruses (HuCVs). HuCVs in stool specimens were detected by reverse transcription-polymerase chain reaction (RT-PCR) using primer pair 289/290, which was designed based on the RNA-dependent RNA polymerase (RdRp) sequence. RT-PCR results were confirmed by sequencing showing that all three outbreak strains belonged to genogroup II of "Norwalk-like viruses" (NLVs). Two strains had high sequence identity with strains in known genetic clusters (Hawaii and Lordsdale clusters). The third strain (MOH) had distinct RdRp sequence, sharing 77/86% (nt/aa) identity with Snow Mountain virus (SMV), the closest genogroup II virus. To characterize MOH further, we cloned, sequenced, and expressed in baculovirus its capsid gene. It had 75/79% (nt/aa) identity with SMV, but 97/98% (nt/aa) identity with NLV/Hillingdon/90/UK, a recently identified genetic cluster of HuCVs. The recombinant MOH (rMOH) capsid protein self-assembled into virus-like particles (VLPs), which is antigenically distinct from other recombinant HuCV capsid antigens available in our laboratory. Further study of this VLP will have important applications in antigenic characterization and diagnosis of HuCVs.

Epidemiology of human Sapporo-like caliciviruses in the South West of England: molecular characterisation of a genetically distinct isolate

Human enteric caliciviruses have been assigned to two distinct genera: the Norwalk-like viruses (NLVs) and the Sapporo-like viruses (SLVs). During a 3-year surveillance of gastroenteritis in the South West of England during November 1997-2000, a total of 27 clinical samples containing SLVs were collected. PCR amplicons covering a region of the RNA polymerase gene were obtained from 18 of the SLV samples. Sequence analysis of the PCR products indicated that the SLV isolates could be assigned to one of the two major genetic groups represented by Sapporo and London/92 caliciviruses. One of these isolates belonging to the London/92 group (Bristol/98) was subjected to a complete genome sequence analysis. The full genomic sequence of the Bristol/98 isolate was determined from RNA extracted from a single stool sample and consists of 7490 nucleotides, excluding the poly(A) tail. The genome is organised into two open reading frames (ORFs), similar to that of Manchester SLV although the small ORF overlapping the region encoding the capsid protein observed in Manchester SLV is absent in Bristol/98 SLV. The polyprotein (ORF1) of Bristol/98 SLV consists of 2,280 amino acids and, as observed in all SLVs, the structural protein is encoded in frame and contiguous with the 3' terminus of the ORF1. Phylogenetic studies based on complete capsid sequences and genome arrangements within the SLVs indicate that the human enteric viruses within the "Sapporo-like" virus clade should be divided into two distinct genetic groups analogous to the assignment of the Norwalk-like viruses.