Prevalence of astroviruses in a children's hospital

Astroviruses in terrestrial Malagasy mammals

Small terrestrial mammals are major hosts of infectious agents responsible for zoonotic diseases. Astroviruses (AstVs)-the cause of non-bacterial gastroenteritis mainly affecting young children-have been detected in a wide array of mammalian and avian host species. However, understanding the factors that influence AstV infection within and across hosts is limited. Here, we investigated the impact of land use changes on AstVs in terrestrial small mammals in rural northeastern Madagascar. We sampled 515 small mammals, representing seven endemic and four introduced species. Twenty-two positive samples were identified, all but one of which were found in the introduced species Mus musculus and Rattus rattus (family Muridae), with a positivity rate of 7.7% (6/78) and 5.6% (15/266), respectively. The non-introduced rodent case was from an endemic shrew-tenrec (family Tenrecidae). We found the highest positivity rate of AstVs infection in brushy regrowth (17.5%, 7/40) as compared to flooded rice fields (4.60%, 8/174), secondary forest (4.1%, 3/74), agroforest (3.6%, 1/28), village (2.61%, 3/115), and semi-intact forest (0%, 0/84). A phylogenetic analysis revealed an association between AstVs and their rodent host species. None of the viruses were phylogenetically related to AstVs previously described in Malagasy bats. This study supports AstV circulation in synanthropic animals in agricultural habitats of Madagascar and highlights the need to assess the spillover risk to human populations in rural areas.

Leveraging machine learning for taxonomic classification of emerging astroviruses

Astroviruses are a family of genetically diverse viruses associated with disease in humans and birds with significant health effects and economic burdens. Astrovirus taxonomic classification includes two genera, Avastrovirus and Mamastrovirus. However, with next-generation sequencing, broader interspecies transmission has been observed necessitating a reexamination of the current host-based taxonomic classification approach. In this study, a novel taxonomic classification method is presented for emergent and as yet unclassified astroviruses, based on whole genome sequence k-mer composition in addition to host information. An optional component responsible for identifying recombinant sequences was added to the method's pipeline, to counteract the impact of genetic recombination on viral classification. The proposed three-pronged classification method consists of a supervised machine learning method, an unsupervised machine learning method, and the consideration of host species. Using this three-pronged approach, we propose genus labels for 191 as yet unclassified astrovirus genomes. Genus labels are also suggested for an additional eight as yet unclassified astrovirus genomes for which incompatibility was observed with the host species, suggesting cross-species infection. Lastly, our machine learning-based approach augmented by a principal component analysis (PCA) analysis provides evidence supporting the hypothesis of the existence of human astrovirus (HAstV) subgenus of the genus Mamastrovirus, and a goose astrovirus (GoAstV) subgenus of the genus Avastrovirus. Overall, this multipronged machine learning approach provides a fast, reliable, and scalable prediction method of taxonomic labels, able to keep pace with emerging viruses and the exponential increase in the output of modern genome sequencing technologies.

Structure and immunogenicity of the murine astrovirus capsid spike

Human astroviruses (HAstVs) are small, non-enveloped icosahedral RNA viruses that are a significant cause of diarrhoea in young children. Despite their worldwide prevalence, HAstV pathogenesis studies and vaccine development remain challenging due to the lack of an animal model for HAstV infection. The recent development of a murine astrovirus (MuAstV) infection model in mice provides the opportunity to test proof-of-concept vaccines based on MuAstV antigens. To help establish a system in which an astrovirus capsid spike-based vaccine could be tested in vivo, we designed and produced a recombinant MuAstV capsid spike protein based on predicted secondary structure homology to HAstV spike proteins. The recombinant MuAstV spike can be expressed with high efficiency in Escherichia coli and retains antigenicity to polyclonal antibodies elicited by MuAstV infection. We determined the crystal structure of the MuAstV spike to 1.75 Å and assessed its structural conservation with HAstV capsid spike. Despite low sequence identity between the MuAstV and HAstV spikes and differences in their overall shapes, they share related structural folds. Additionally, we found that vaccination with MuAstV spike induced anti-MuAstV-spike antibodies, highlighting that the recombinant spike is immunogenic. These studies lay a foundation for future in vivo MuAstV challenge studies to test whether MuAstV spike can be the basis of an effective vaccine.

Clinical and Epidemiologic Features of Viral Gastroenteritis in Hospitalized Children: An 11-Year Surveillance in Palermo (Sicily)

In order to acquire information regarding viral agents and epidemiologic features of severe paediatric Viral Acute Gastroenteritis (VAGE) across multiple seasons in the pre-rotavirus-vaccine era, the epidemiologic characteristics of VAGE were investigated among paediatric patients hospitalized in a major Sicilian paediatric hospital from 2003 to 2013. Overall, 4725 children were observed and 2355 (49.8%) were diagnosed with a viral infection: 1448 (30.6%) were found positive to rotavirus, 645 (13.7%) to norovirus, 216 (4.6%) to adenovirus, and 46 (0.97%) to astrovirus. Viral infections showed different patterns of hospitalization in terms of age at risk (younger for rotavirus and adenovirus infections), seasonality (increased risk in winter for rotavirus and norovirus), trend over time (reduced risk in 2011-2013 for norovirus and rotavirus) and major diagnostic categories (digestive diseases more frequent in adenovirus and astrovirus but not in norovirus). This study increases general knowledge of VAGE epidemiology and contributes to suggest some a priori diagnostic criteria that could help clinicians to identify and treat viral agents responsible for gastroenteritis in hospital settings.

Occurrence of Human Enteric Viruses in Water Sources and Shellfish: A Focus on Africa

Enteric viruses are a diverse group of human pathogens which are primarily transmitted by the faecal-oral route and are a major cause of non-bacterial diarrhoeal disease in both developed and developing countries. Because they are shed in high numbers by infected individuals and can persist for a long time in the environment, they pose a serious threat to human health globally. Enteric viruses end up in the environment mainly through discharge or leakage of raw or inadequately treated sewage into water sources such as springs, rivers, dams, or marine estuaries. Human exposure then follows when contaminated water is used for drinking, cooking, or recreation and, importantly, when filter-feeding bivalve shellfish are consumed. The human health hazard posed by enteric viruses is particularly serious in Africa where rapid urbanisation in a relatively short period of time has led to the expansion of informal settlements with poor sanitation and failing or non-existent wastewater treatment infrastructure, and where rural communities with limited or no access to municipal water are dependent on nearby open water sources for their subsistence. The role of sewage-contaminated water and bivalve shellfish as vehicles for transmission of enteric viruses is well documented but, to our knowledge, has not been comprehensively reviewed in the African context. Here we provide an overview of enteric viruses and then review the growing body of research where these viruses have been detected in association with sewage-contaminated water or food in several African countries. These studies highlight the need for more research into the prevalence, molecular epidemiology and circulation of these viruses in Africa, as well as for development and application of innovative wastewater treatment approaches to reduce environmental pollution and its impact on human health on the continent.

Complement Evasion Strategies of Viruses: An Overview

Being a major first line of immune defense, the complement system keeps a constant vigil against viruses. Its ability to recognize large panoply of viruses and virus-infected cells, and trigger the effector pathways, results in neutralization of viruses and killing of the infected cells. This selection pressure exerted by complement on viruses has made them evolve a multitude of countermeasures. These include targeting the recognition molecules for the avoidance of detection, targeting key enzymes and complexes of the complement pathways like C3 convertases and C5b-9 formation - either by encoding complement regulators or by recruiting membrane-bound and soluble host complement regulators, cleaving complement proteins by encoding protease, and inhibiting the synthesis of complement proteins. Additionally, viruses also exploit the complement system for their own benefit. For example, they use complement receptors as well as membrane regulators for cellular entry as well as their spread. Here, we provide an overview on the complement subversion mechanisms adopted by the members of various viral families including Poxviridae, Herpesviridae, Adenoviridae, Flaviviridae, Retroviridae, Picornaviridae, Astroviridae, Togaviridae, Orthomyxoviridae and Paramyxoviridae.

Novel human astroviruses: Novel human diseases?

Astroviruses are small, non-enveloped, single-stranded positive RNA viruses that belong to the Astroviridae family. While classical human astroviruses (HAstV) are a well-recognized cause of acute non-bacterial diarrhea among young children worldwide, novel astroviruses, named HAstV-MLB and HAstV-VA/HMO, have been identified recently in humans by molecular assays. They are phylogenetically more related to animal astroviruses than to classical human astroviruses, thus suggesting cross-species transmission. Serological studies demonstrated a surprisingly high seroprevalence in certain populations and highlighted a high infection rate in the early years of life. Although their pathogenic role has not yet been clearly determined, novel astrovirus RNA sequences have been identified in different biological specimens of symptomatic patients, including the feces, plasma, cerebrospinal fluid, and brain biopsies. Thus, there is evidence that they could contribute not only to digestive tract infection, but also to unexpected clinical syndromes, notably encephalitis and meningitis. Severe infections affect mainly immunocompromised patients. These findings indicate that novel astroviruses should be considered in the differential diagnosis of immunocompromised patients with meningitis or encephalitis of unknown origin.

The role of Clostridium difficile in the paediatric and neonatal gut - a narrative review

Clostridium difficile is an important nosocomial pathogen in adults. Its significance in children is less well defined, but cases of C. difficile infection (CDI) appear to be increasingly prevalent in paediatric patients. This review aims to summarize reported Clostridium difficile carriage rates across children of different age groups, appraise the relationship between CDI and factors such as method of delivery, type of infant feed, antibiotic use, and co-morbidities, and review factors affecting the gut microbiome in children and the host immune response to C. difficile. Searches of PubMed and Google Scholar using the terms 'Clostridium difficile neonates' and 'Clostridium difficile children' were completed, and reference lists of retrieved publications screened for further papers. In total, 88 papers containing relevant data were included. There was large inter-study variation in reported C. difficile carriage rates. There was an association between CDI and recent antibiotic use, and co-morbidities such as immunosuppression and inflammatory bowel disease. C. difficile was also found in stools of children with diarrhoea attributed to other pathogens (e.g. rotavirus). The role of C. difficile in the paediatric gut remains unclear; is it an innocent bystander in diarrhoeal disease caused by other organisms, or a pathogen causing subclinical to severe symptoms? Further investigation of the development of serological and local host response to C. difficile carriage may shed new light on disease mechanisms. Work is underway on defining a framework for diagnosis and management of paediatric CDI.

Co-infection as a confounder for the role of Clostridium difficile infection in children with diarrhoea: a summary of the literature

Although Clostridium difficile is a major cause of antibiotic-associated diarrhoea in adults, the incidence and severity of C. difficile infection (CDI) in children is unclear. One complicating factor in assessing the role of CDI in children is the possibility of co-infection with other gastrointestinal pathogens. In this review, we summarise the literature concerning C. difficile co-infections in young children, in an attempt to discuss the rate of co-infections and their potential role in the severity of CDI clinical presentation. We identified 31 studies where co-infections were analysed, comprising 1,718 patients with positive C. difficile tests. The pooled percentage of reported co-infections was 20.7% (range 0-100%). Viral co-infections were most commonly reported (46%), with bacteria and parasites accounting for 14.9% and 0.01% of cases, respectively. However, the panel of co-infections tested for varied considerably among studies and 38% of stated co-infections did not have a pathogen reported. Substantial variation in how and when tests for gastrointestinal co-infections are carried out, small sample sizes and a lack of clear CDI case definitions preclude meaningful conclusions on the true rate of co-infections in this patient population. This review suggests that co-infections may be common in children with diarrhoea who tested positive for C. difficile. Given a lack of CDI case definitions, especially in young children under the age of 5 years, a broad panel of pathogens should be tested for to exclude other microbiological causes. However, the summarised poor quality of the available literature on this subject highlights a need for further studies.

The prevalence of norovirus, astrovirus and adenovirus infections among hospitalised children with acute gastroenteritis in Porto Velho, state of Rondônia, western Brazilian Amazon

Although viruses are well-established causes of acute gastroenteritis, few data on the circulation of these pathogens in Porto Velho, state of Rondônia, Brazil, are available. Thus, faecal samples from hospitalised diarrhoeic children, under six years of age, were collected and tested for the presence of norovirus (NoV), adenovirus (AdV) and astrovirus (AstV) from February 2010-February 2012. Specimens were screened by reverse-transcription polymerase chain reaction and viruses were found in 10.7% (63/591) of the cases. NoV, AdV and AstV were detected in 7.8%, 2% and 0.8% of the samples, respectively. NoV infection was observed at all ages and was most prevalent in zero-18-month-old children (84.7%; p = 0.002). A higher incidence of NoV was detected from February-April 2010, when it was found in 52.2% of the cases. Co-infections involving these viruses, rotavirus and enteropathogenic bacteria were detected in 44.4% (28/63) of the children with viral diarrhoea. Nosocomial infections were demonstrated in 28.6% (18/63) of the cases in which viruses were detected. The present paper reports, for the first time, the circulation of NoV and AstV among the paediatric population of Porto Velho and it contributes to our understanding of the roles of these pathogens in gastrointestinal infections.

Human astroviruses

Human astroviruses (HAtVs) are positive-sense single-stranded RNA viruses that were discovered in 1975. Astroviruses infecting other species, particularly mammalian and avian, were identified and classified into the genera Mamastrovirus and Avastrovirus. Through next-generation sequencing, many new astroviruses infecting different species, including humans, have been described, and the Astroviridae family shows a high diversity and zoonotic potential. Three divergent groups of HAstVs are recognized: the classic (MAstV 1), HAstV-MLB (MAstV 6), and HAstV-VA/HMO (MAstV 8 and MAstV 9) groups. Classic HAstVs contain 8 serotypes and account for 2 to 9% of all acute nonbacterial gastroenteritis in children worldwide. Infections are usually self-limiting but can also spread systemically and cause severe infections in immunocompromised patients. The other groups have also been identified in children with gastroenteritis, but extraintestinal pathologies have been suggested for them as well. Classic HAstVs may be grown in cells, allowing the study of their cell cycle, which is similar to that of caliciviruses. The continuous emergence of new astroviruses with a potential zoonotic transmission highlights the need to gain insights on their biology in order to prevent future health threats. This review focuses on the basic virology, pathogenesis, host response, epidemiology, diagnostic assays, and prevention strategies for HAstVs.

Peptide inhibitor of complement c1, a novel suppressor of classical pathway activation: mechanistic studies and clinical potential

The classical pathway of complement plays multiple physiological roles including modulating immunological effectors initiated by adaptive immune responses and an essential homeostatic role in the clearance of damaged self-antigens. However, dysregulated classical pathway activation is associated with antibody-initiated, inflammatory diseases processes like cold agglutinin disease, acute intravascular hemolytic transfusion reaction (AIHTR), and acute/hyperacute transplantation rejection. To date, only one putative classical pathway inhibitor, C1 esterase inhibitor (C1-INH), is currently commercially available and its only approved indication is for replacement treatment in hereditary angioedema, which is predominantly a kinin pathway disease. Given the variety of disease conditions in which the classical pathway is implicated, development of therapeutics that specifically inhibits complement initiation represents a major unmet medical need. Our laboratory has identified a peptide that specifically inhibits the classical and lectin pathways of complement. In vitro studies have demonstrated that these peptide inhibitors of complement C1 (PIC1) bind to the collagen-like region of the initiator molecule of the classical pathway, C1q. PIC1 binding to C1q blocks activation of the associated serine proteases (C1s–C1r–C1r–C1s) and subsequent downstream complement activation. Rational design optimization of PIC1 has resulted in the generation of a highly potent derivative of 15 amino acids. PIC1 inhibits classical pathway mediated complement activation in ABO incompatibility in vitro and inhibiting classical pathway activation in vivo in rats. This review will focus on the pre-clinical development of PIC1 and discuss its potential as a therapeutic in antibody-mediated classical pathway disease, specifically AIHTR.

Incubation periods of viral gastroenteritis: a systematic review

BACKGROUND

Accurate knowledge of incubation period is important to investigate and to control infectious diseases and their transmission, however statements of incubation period in the literature are often uncited, inconsistent, and/or not evidence based.

METHODS

In a systematic review of the literature on five enteric viruses of public health importance, we found 256 articles with incubation period estimates, including 33 with data for pooled analysis.

RESULTS

We fit a log-normal distribution to pooled data and found the median incubation period to be 4.5 days (95% CI 3.9-5.2 days) for astrovirus, 1.2 days (95% CI 1.1-1.2 days) for norovirus genogroups I and II, 1.7 days (95% CI 1.5-1.8 days) for sapovirus, and 2.0 days (95% CI 1.4-2.4 days) for rotavirus.

CONCLUSIONS

Our estimates combine published data and provide sufficient quantitative detail to allow for these estimates to be used in a wide range of clinical and modeling applications. This can translate into improved prevention and control efforts in settings with transmission or the risk of transmission.

The role of torovirus in nosocomial viral gastroenteritis at a large tertiary pediatric centre

OBJECTIVE

To describe the viral etiology and epidemiology of nosocomial viral gastroenteritis (NVG) at a tertiary care pediatric hospital and identify any changes over the past two decades.

METHODS

Retrospective review of all patients with laboratory-confirmed NVG at The Hospital for Sick Children (Toronto, Ontario), from January 1, 2004, to December 31, 2005.

RESULTS

One hundred forty-two episodes of NVG were found among 133 patients, occurring in 0.48 of 100 admissions. The median age was two years; 42% were <1 year of age and 41% were immunocompromised. The most commonly detected pathogen was torovirus (67% of episodes), followed by rotavirus (19%) and adenovirus (9%). Seventy-five cases (53%) were epidemiologically linked in 32 separate clusters (median cluster size two, range two to four). The NVG rate fell from 0.63 of 100 to 0.22 of 100 admissions after March 2005 (P<0.001) when enhanced infection control precautions were instituted in response to an outbreak of vancomycin-resistant Enterococcus.

CONCLUSIONS

Torovirus remains the most commonly identified cause of NVG at The Hospital for Sick Children. Most NVG cases were epidemiologically linked, and a significant reduction in cases occurred after the institution of enhanced infection control practices following an outbreak of vancomycin-resistant Enterococcus. Improved education and surveillance for NVG should lead to further reduction in this problem.

Adaptive immunity restricts replication of novel murine astroviruses

The mechanisms of astrovirus pathogenesis are largely unknown, in part due to a lack of a small-animal model of disease. Using shotgun sequencing and a custom analysis pipeline, we identified two novel astroviruses capable of infecting research mice, murine astrovirus (MuAstV) STL1 and STL2. Subsequent analysis revealed the presence of at least two additional viruses (MuAstV STL3 and STL4), suggestive of a diverse population of murine astroviruses in research mice. Complete genomic characterization and subsequent phylogenetic analysis showed that MuAstV STL1 to STL4 are members of the mamastrovirus genus and are likely members of a new mamastrovirus genogroup. Using Rag1(-/-) mice deficient in B and T cells, we demonstrate that adaptive immunity is required to control MuAstV infection. Furthermore, using Stat1(-/-) mice deficient in innate signaling, we demonstrate a role for the innate immune response in the control of MuAstV replication. Our results demonstrate that MuAstV STL permits the study of the mechanisms of astrovirus infection and host-pathogen interactions in a genetically manipulable small-animal model. Finally, we detected MuAstV in commercially available mice, suggesting that these viruses may be present in academic and commercial research mouse facilities, with possible implications for interpretation of data generated in current mouse models of disease.

Epidemiology of astrovirus infection in children

Human astrovirus (HAstV) is a major cause of acute diarrhea among children, resulting in outbreaks of diarrhea and occasionally hospitalization. Improved surveillance and application of sensitive molecular diagnostics have further defined the impact of HAstV infections in children. These studies have shown that HAstV infections are clinically milder (diarrhea, vomiting, fever) than infections with other enteric agents. Among the 8 serotypes of HAstV identified, serotype 1 is the predominant strain worldwide. In addition to serotype 1, the detection rate of HAstV types 2 to 8 has increased by using newly developed assays. HAstV is less common compared with other major gastroenteritis viruses, including norovirus and rotavirus; however, it is a potentially important viral etiological agent with a significant role in acute gastroenteritis. A better understanding of the molecular epidemiology and characteristics of HAstV strains may be valuable to develop specific prevention strategies.

Identification of two immunoreactive peptides useful for the detection of porcine astrovirus

Porcine astroviruses (PAstVs) are small RNA viruses associated with gastroenteritis. The capsid polyprotein of PAstVs, human (HAstVs) and feline (FAstVs) AstVs has a high similarity at the N-terminus before residue 415. Previous results showed the cross-detection of PAstVs and HAstVs from diarrheal samples using a commercial ELISA test that uses a monoclonal antibody to capture HAstVs, suggesting the existence of common immunoreactive epitopes between these two virus types. In this study, we seeked immunoreactive peptides located in the PAstV capsid that may be potentially used for their specific detection. The variability and hydrophobicity of a short fragment of 132 amino acids were analyzed using several capsid sequences of PAstVs and HAstVs. Peptides TATL, SLNP and IDIV were selected, synthesized and inoculated into rabbits. Pre- and hyperimmune sera were collected and their reactivity was examined by immunoassay and immunofluorescence against two wild-type strains of PAstV adapted to grow in cell culture, observing reactivity in two of the sera. Finally, the possible cross-reactivity of the sera against HAstVs was partially ruled out using HAstV8. Our data suggest that TATLGTIGSNSSGKTELEAC and IDIVVGKAATFNLKASDLSGP peptides represent immunoreactive regions useful for the specific detection of PAstVs.

[Rotavirus and other viruses causing acute childhood gastroenteritis]

Acute gastroenteritis is one of the most common diseases, affecting children worldwide. Viruses are recognized as a major cause of this disease, particularly in children. Since the Norwalk virus was identified as a cause of gastroenteritis, the number of viral agents associated with diarrheal disease in humans has progressively increased. Rotavirus is the most common cause of severe diarrhea in children under 5 years of age. Human astroviruses, caliciviruses and enteric adenovirus are also important etiologic agents of acute gastroenteritis. Other viruses such as toroviruses, coronaviruses, picobirnaviruses, Aichi virus and human bocavirus are increasingly being identified as causative agents of diarrhea. Vaccination against rotavirus could prevent cases of severe diarrhea and reduce the mortality attributable to this disease.

Contamination of the hospital environment with gastroenteric viruses: comparison of two pediatric wards over a winter season

The aims of this study were to examine the extent of gastroenteric virus contamination in a pediatric primary immunodeficiency (PPI) ward and a general pediatric ward over a winter season and to determine whether changes to hospital infection control interventions would have an impact on environmental contamination levels within pediatric units. Environmental swabs were collected weekly from 11 sites in both wards from 15 December 2005 to 3 March 2006 and examined for the presence of norovirus (NoV), astrovirus, and rotavirus (RV) by reverse transcriptase PCR. Viruses were detected in 17% and 19% of swabs from both wards. Virus contamination for NoV and RV decreased from 20% to 6% and 15% to 10% of swabs, respectively, in the PPI ward from the 2004 study by Gallimore et al. (C. I. Gallimore, C. Taylor, A. R. Gennery, A. J. Cant, A. Galloway, M. Iturriza-Gomara, and J. J. Gray, J. Clin. Microbiol. 44:395-399, 2006). Overall, changes to cleaning protocols were deemed to have reduced the level of environmental contamination with gastroenteric viruses, but contamination still occurred due to a breakdown in infection control procedures indicated by contamination in areas frequented by parents but used only occasionally by staff.

Human astrovirus coat protein inhibits serum complement activation via C1, the first component of the classical pathway

Human astroviruses (HAstVs) belong to a family of nonenveloped, icosahedral RNA viruses that cause noninflammatory gastroenteritis, predominantly in infants. Eight HAstV serotypes have been identified, with a worldwide distribution. While the HAstVs represent a significant public health concern, very little is known about the pathogenesis of and host immune response to these viruses. Here we demonstrate that HAstV type 1 (HAstV-1) virions, specifically the viral coat protein (CP), suppress the complement system, a fundamental component of the innate immune response in vertebrates. HAstV-1 virions and purified CP both suppress hemolytic complement activity. Hemolytic assays utilizing sera depleted of individual complement factors as well as adding back purified factors demonstrated that HAstV CP suppresses classical pathway activation at the first component, C1. HAstV-1 CP bound the A chain of C1q and inhibited serum complement activation, resulting in decreased C4b, iC3b, and terminal C5b-9 formation. Inhibition of complement activation was also demonstrated for HAstV serotypes 2 to 4, suggesting that this phenomenon is a general feature of these human pathogens. Since complement is a major contributor to the initiation and amplification of inflammation, the observed CP-mediated inhibition of complement activity may contribute to the lack of inflammation associated with astrovirus-induced gastroenteritis. Although diverse mechanisms of inhibition of complement activation have been described for many enveloped animal viruses, this is the first report of a nonenveloped icosahedral virus CP inhibiting classical pathway activation at C1.

[Viral gastroenteritis. Application of a protocol for astrovirus detection in childhood gastroenteritis]

BACKGROUND AND OBJECTIVE

Diagnosis of viral gastroenteritis is an important subject in clinical virology which is mainly determined by the availability of reagents in laboratories, such as in the case of astrovirus. The aim of this study was to estimate the increase in the diagnostic performance achieved after the incorporation of astrovirus search in the diagnosis protocol of acute viral gastroenteritis. We also analyzed the trend of infections in other more commonly searched virus, such as rotavirus and enteric adenovirus.

MATERIAL AND METHODS

Retrospective study during 20 years that included 12,980 stool samples processed for gastroenteritis virus diagnosis. Since 1997 an enzyme immunoassay for astrovirus has been applied to those samples that are negative for rotavirus and adenovirus. The study was divided in two periods (1986-1996 and 1997-2005, without and with astrovirus diagnosis) and the percentage of patients diagnosed in each period was compared. The trend of positive results as well as the percentage of positive results over all patients studied was modelled using the least squares method.

RESULTS

The percentages of positive patients for rotavirus, adenovirus and astrovirus were 10.3%, 2.3% and 6.0% respectively, and there were uncommon co-infections by rotavirus and adenovirus (0.2%). The protocol applied to the astrovirus diagnosis increased the diagnosis rate up to 16.8% of the studied cases. Significant statistical differences were observed between the 2 study periods. A quadratic growth was observed in the results of positive diagnosis of viral gastroenteritis during the study period.

CONCLUSIONS

The search of astrovirus in gastroenteritis cases by a selective protocol increased the diagnostic performance of gastrointestinal virus by 6%. In view of these results, it would be useful to implement astrovirus diagnosis in faeces with liquid or semi-liquid consistency when rotavirus and adenovirus detection is negative.

Nosocomial diarrhoea

Toroviruses have been reported as a new cause of nosocomial viral diarrhoea, and the role of astroviruses has been further elucidated. Polymerase chain reaction methods promise to improve the diagnosis and understanding of the aetiology and control of hospital-acquired viral gastroenteritis. A clearer picture of the impact and extent of Clostridium difficile diarrhoea has emerged, and several control measures have been described. An epidemic Clostridium difficile strain and toxin A-deficient strains have been reported. There is growing evidence that enterotoxin-producing Clostridium perfringens can also cause antibiotic-associated diarrhoea.

Development of a one step real-time RT-PCR method for sensitive detection of human astrovirus

Human astrovirus (HAstV) has been recognized as the second most common cause of diarrhoea among children under 5 years old. To date, the true incidence of HAstV was underestimated when using enzyme immunoabsorbent assays (EIAs) and conventional reverse transcription (RT)-polymerase chain reaction (PCR) methods. The sensitivity of detection of EIA is insufficient and, although RT-PCR is more sensitive than EIA, the time required is a limitation for astrovirus detection. The aim of the study was to develop a real-time RT-PCR method in order to increase the sensitivity, to quantify the viral load and to minimize the time required for HAstV detection. The real-time RT-PCR reported here requires only one rapid step to obtain a high sensitivity (0.0052 infectious units (IU) (0.0026 IU/microl)) in all human astrovirus detected. The real-time RT-PCR detected IUs down to a 10(-6) dilution with an improvement in the detection limit of factor 10(4), whereas the conventional RT-PCR detected down to IUs 10(-2) dilution. This process is able to reduce the time of the assay and avoids the risk of contamination. The method described below has been validated with a panel of 100 clinical samples and the results obtained confirmed the high specificity of the assay; consequently, the application of this assay for molecular diagnosis is feasible as a versatile tool for ascertaining the true implication of HAstV in acute viral gastroenteritis.

Environmental monitoring for gastroenteric viruses in a pediatric primary immunodeficiency unit

The aim of this study was to determine if gastroenteric viruses were present on surfaces and equipment in a pediatric primary immunodeficiency unit (PPIU) by environmental sampling using swabs and subsequent nucleic acid extraction and reverse transcriptase PCR assays. A PPIU was chosen, and 11 swabs were taken at the same sites every 2 weeks for 6 months. Nested/heminested PCR assays were used to screen for astroviruses (AsV), noroviruses (NoV), and rotaviruses (RV). AsV, NoV, and RV were detected at multiple swab sites during the study period. NoV was the most frequently detected virus on environmental surfaces; however, RV was detected on 79% and NoV on 50% of swabbing dates during the study period. Toilet taps were the most contaminated sites. Fecal samples from selected patients in the unit were also screened during the study period, and patients excreted AsV, NoV, and RV at times during the study. New cleaning schedules and changes in some of the PPIU sanitary furniture have been suggested as a means of reducing environmental contamination.

Development of antigen-capture enzyme-linked immunosorbent assay and RT-PCR for detection of turkey astroviruses

Turkey astrovirus (TAstV) is an important agent of poult enteritis. The diagnosis of astroviruses has been dependent mainly on electron microscopy (EM) or immune EM (IEM). To develop other simple, rapid, and reliable diagnostic assays, two antigen-capture enzyme-linked immunosorbent assays (AC-ELISAs), polyclonal AC-ELISA and monoclonal AC-ELISA, were developed in this study. Monoplex and multiplex reverse transcription-polymerase chain reactions (RT-PCRs) were also developed using nondegenerate primer sets specific to the capsid region and degenerate primer pairs specific to the polymerase area of two TAstV. EM was included for comparison. Fecal or intestinal contents samples from naturally and experimentally infected poults with enteritis were examined using the developed assays. The polyclonal AC-ELISA had higher sensitivity and wider detection spectrum than the monoclonal AC-ELISA with group-specific monoclonal antibody (MAb), whereas the monoclonal AC-ELISA had very high specificity but lower sensitivity, which was estimated at 0.06 microg of viral proteins. Small round viruses (SRV) that could be astroviruses or other small viruses were detected in 34.4% of the samples examined by EM. The monoplex RT-PCR results amplified with primers SRV-1-3 and SRV-1-5 revealed that the positive rate of astroviruses was 45.3%, which was 10.9% higher than that of EM even if other SRVs were not excluded. Multiplex RT-PCR with SRV-1-3 and SRV-1-5 and AFCP-F1 and AFCP-R1 and the monoplex RT-PCR with degenerate primers verified that the positive rate of astroviruses was 59.4%, which was 25% higher than that of EM. Both RT-PCRs showed good specificity and wider detection spectrum compared with earlier published data.

Reverse transcriptase-PCR for the detection of Astrovirus in children with nosocomial acute diarrhoea in Naples, Italy

OBJECTIVE

This study was made to determine the incidence of nosocomial viral gastroenteritis in all children aged 0-4 years, admitted in the Pediatric Hospital over a 3-year period.

METHODS

Astrovirus was detected by reverse transcriptase-PCR; routine diagnostic tests for Rotavirus, Adenovirus, and common bacterial pathogens were carried out on all samples.

RESULTS

Of the 460 children with nosocomial diarrhea, 23 harbored Astrovirus (5%). Most cases occurred during the coldest months of the year. Children under 1 year of age were the most susceptible population.

CONCLUSION

The collected data confirms the importance of viral etiology in nosocomial gastroenteritis. The reported rate of detection stresses the importance of Astrovirus in pediatric diarrhea. The authors recommend screening for this virus on a routine basis.

Use of a heminested reverse transcriptase PCR assay for detection of astrovirus in environmental swabs from an outbreak of gastroenteritis in a pediatric primary immunodeficiency unit

An outbreak of astrovirus gastroenteritis occurred in the Primary Immunodeficiency Unit at Newcastle General Hospital in March 2004. Environmental swabbing of the unit was undertaken after the outbreak, with multiple sites swabbed pre- and postcleaning. Astroviruses were detected in four environmental swabs and from two patient fecal samples using heminested reverse transcriptase PCR. An astrovirus genotype 3 strain was identified in both environmental swabs and fecal specimens and was the strain identified as being responsible for the outbreak. Environmental transmission of the virus was thought to have occurred by contamination of a syringe pump outside the laminar-flow curtain of a patient who was admitted with astrovirus gastroenteritis. This was subsequently transmitted to a cubicle next door and to a television/games console in a parents' room in the ward. Environmental monitoring of surfaces/equipment, using PCR assays for gastroenteric viruses in hospital situations where infection can give rise to serious clinical complications, may have a role in controlling and monitoring cleaning and the subsequent prevention of nosocomial transmission of gastroenteritis.

Comparison of clinical characteristics between astrovirus and rotavirus infections diagnosed in 1997 to 2002 in Hungary

AIM

To determine the severity and clinical characteristics of human astrovirus (HAstV) infections among hospitalized children and compare them with children infected by rotavirus.

METHODS

Retrospective, case-control study of astrovirus-infected and rotavirus-infected children. Astroviruses were detected in stool samples by enzyme immunoassay and/or reverse transcriptase-polymerase chain reaction. All stool samples were tested for rotavirus and bacterial pathogens, and all negative samples were further tested for human astrovirus. Children with astrovirus-positive stool samples and complete clinical data were included in this study.

RESULTS

Astrovirus was detected in 29 (1.8%) children, and 63 rotavirus-infected children were included as controls. Astrovirus-infected children had shorter duration of diarrhea than rotavirus-infected children (median 4 and 6 d, respectively; p<0.05), and 79% of the astrovirus infections were associated with a short duration of vomiting (median 1 and 4 d, respectively; p<0.0001). Rotavirus-infected children had longer hospitalization (p<0.050) than astrovirus-infected children.

CONCLUSION

HAstV-infected children had similar symptoms to those occurring in rotavirus infection. However, astrovirus-infected patients had a significantly shorter duration of diarrhea and vomiting, and they required a shorter hospitalization. On the basis of the clinical data and severity scores, children with rotavirus infection had more severe illness.

Immunity and Resistance to Astrovirus Infection

Astroviruses are one of the leading causes of acute viral enteritis in infants, and are recognized as a clinically important pathogen in the elderly and the immunocompromised. In spite of this, we still know very little about the immune response to astrovirus infection. Clinical observations and human volunteer studies have indicated a role for the humoral response and suggest neutralizing antibodies are important in limiting infection. Studies of human intestinal biopsies have suggested that cellular immunity; specifically CD4(+) T-cells may also be involved in the anti-astrovirus response. Additionally, various animal models have indicated potential roles for the innate immune system in controlling infections. How these various effector arms of the immune system collaborate to result in immunity and resistance to astrovirus infection is still unknown. This review summarizes our current understanding of the immune response to this pathogen and highlights the key concepts that still need to be addressed. Until we understand the role of the immune system in astrovirus infection or other enteric viruses, we will continue to be limited in our ability to treat and control gastrointestinal diseases.

One-year survey of astrovirus infection in children with gastroenteritis in a large hospital in Hungary: Occurrence and genetic analysis of astroviruses

Human astroviruses (HAstV) are the causative agents of viral gastroenteritis mainly in children worldwide. This study investigated the epidemiology and genotype diversity of HAstVs detected in children admitted to hospital with gastroenteritis in Hungary. Stool samples were collected from children with diarrhea at the Municipal "Szent László" Hospital, Budapest, Hungary, between January 2002 and December 2002. Of 2,758 samples, 607 were negative for both rotaviruses and bacterial pathogens and were tested for astroviruses using a reverse transcriptase-polymerase chain reaction (RT-PCR) targeting the open reading frame (ORF2), capsid region. Astrovirus was detected in 10 samples (1.6%) by RT-PCR. Astrovirus infection was more frequent among children 49 to 60 months of age. Genotyping of positive samples was performed by type-specific RT-PCR and confirmed by sequence analysis. Phylogenetic analysis was performed using a 203 nucleotide consensus length of the 3'-end of the capsid gene. Type-specific RT-PCR and sequence analysis detected genotypes 1 (50%), 4 (30%), 3 (10%), and 8 (10%) among the children admitted to hospital. Genotype 1 was the predominant genotype, but genotypes 3, 4, and 8 were also present indicating the importance of emerging genotype 8 infections. Two distinct genotype 4 variants were observed during this study. Sequence analysis confirmed type-specific RT-PCR results in the capsid region. This is the first comprehensive report on the occurrence of HAstV infections in Central/Eastern Europe.

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.

Prevalence and genetic diversity of human astroviruses in Mexican children with symptomatic and asymptomatic infections

The prevalence and type diversity of human astroviruses (HAstV) in children with symptomatic and asymptomatic infections were determined in five localities of Mexico. HAstV were detected in 4.6 (24 of 522) and 2.6% (11 of 428) of children with and without diarrhea, respectively. Genotyping of the detected strains showed that at least seven (types 1 to 4 and 6 to 8) of the eight known HAstV types circulated in Mexico between October 1994 and March 1995. HAstV types 1 and 3 were the most prevalent in children with diarrhea, although they were not found in all localities studied. HAstV type 8 was found in Mexico City, Monterrey, and Mérida; in the last it was as prevalent (40%) as type 1 viruses, indicating that this astrovirus type is more common than previously recognized. A correlation between the HAstV infecting type and the presence or absence of diarrheic symptoms was not observed. Enteric adenoviruses were also studied, and they were found to be present in 2.3 (12 of 522) and 1.4% (6 of 428) of symptomatic and asymptomatic children, respectively.

Gastroenteritis aguda nosocomial e infección asintomática por rotavirus y astrovirus en niños hospitalizados

BACKGROUND

Nosocomial gastroenteritis is frequent in pediatric hospital wards. Between 20% and 50% of gastroenteritis cases caused by rotavirus and astrovirus are of nosocomial origin.

OBJECTIVE

To determine the incidence of nosocomial rotavirus and astrovirus gastroenteritis in our environment, the incidence of asymptomatic infection with these viruses, and to identify the G serotypes of the rotaviruses detected.

METHODS

We performed a prospective study of all children under 2 years of age admitted to a neonatology unit over a 1-year period who were followed-up for the presence of diarrhea and periodic study of feces to detect the presence of rotavirus and astrovirus antigens by enzyme immunoassay (EIA). Patients with gastroenteritis also underwent bacteria stool culture, adenovirus detection by EIA, calcivirus detection by polymerase chain reaction, and analysis of rotavirus G serotypes by EIA with monoclonal antibodies.

RESULTS

Of 666 children admitted without diarrhea, 60 presented nosocomial gastroenteritis (9 % of patients admitted and 1.75 per 100 days of hospital stay): 34 presented rotavirus (5 % of patients) and two presented astrovirus (0.3 % of patients). Of the 329 patients without diarrhea who were studied, viral elimination was detected in 27: rotavirus in 23 patients and astrovirus in four. Viral infection was detected on admission in 13 patients (4 %) and after 72 hours in 14 patients (4.2 %) (asymptomatic nosocomial infection). No differences in the distribution of rotavirus G serotypes were observed between community-acquired and nosocomial gastroenteritis.

CONCLUSIONS

These data confirm the importance of viral etiology in nosocomial gastroenteritis and allow us to evaluate asymptomatic fecal elimination of rotavirus as one of the factors in the transmission of this infection.

Astrovirus induces diarrhea in the absence of inflammation and cell death

Astroviruses are a leading cause of infantile viral gastroenteritis worldwide. Very little is known about the mechanisms of astrovirus-induced diarrhea. One reason for this is the lack of a small-animal model. Recently, we isolated a novel strain of astrovirus (TAstV-2) from turkeys with the emerging infectious disease poult enteritis mortality syndrome. In the present studies, we demonstrate that TAstV-2 causes growth depression, decreased thymus size, and enteric infection in infected turkeys. Infectious TAstV-2 can be recovered from multiple tissues, including the blood, suggesting that there is a viremic stage during infection. In spite of the severe diarrhea, histopathologic changes in the intestine were mild and there was a surprising lack of inflammation. This may be due to the increased activation of the potent immunosuppressive cytokine transforming growth factor beta during astrovirus infection. These studies suggest that the turkey will be a useful small-animal model with which to study astrovirus pathogenesis and immunity.

Development of a rapid method using nucleic acid sequence-based amplification for the detection of astrovirus

We have developed a rapid method to detect astrovirus in fecal specimens utilizing nucleic acid sequence-based amplification (NASBA) and several detection methodologies, including a sandwich hybridization assay based on DNA-tagged liposomes (liposome-strip detection assay). RNA was extracted from 65 stool specimens that were positive for astrovirus by enzyme immunoassay and was amplified by both NASBA and reverse transcriptase PCR (RT-PCR). Also extracted and amplified were 19 specimens containing rotavirus, 20 specimens containing norovirus, five specimens containing adenovirus, 15 water negative control specimens, and eight specimens containing astrovirus reference strains. NASBA products were detected by electrochemiluminescence detection (ECL) and by liposome-strip detection; RT-PCR products were detected by ethidium bromide staining following gel electrophoresis and by liquid hybridization assay (LHA). There was no significant difference in the detection rates of NASBA- and RT-PCR-based assays, with one exception in which the NASBA/ECL assay detected astrovirus in eight specimens that tested negative by the RT-PCR/LHA assay. These results suggest that these NASBA-based detection methods have detection rates that are as good as or better than those of RT-PCR-based methods. Both NASBA and liposome-strip detection may be useful for field studies and environmental testing because these methods are rapid and do not require specialized equipment.

Viruses causing gastroenteritis

Acute gastroenteritis is one of the most common diseases in humans worldwide. Viruses are recognized as important causes of this disease, particularly in children. Since the Norwalk virus was identified as a cause of gastroenteritis, the number of viral agents associated with diarrheal disease in humans has steadily increased. Rotavirus is the most common cause of severe diarrhea in children under 5 years of age. Astrovirus, calicivirus and enteric adenovirus are also important etiologic agents of acute gastroenteritis. Other viruses, such as toroviruses, coronaviruses, picobirnaviruses and pestiviruses, are increasingly being identified as causative agents of diarrhea. In recent years, the availability of diagnostic tests, mainly immunoassays or molecular biology techniques, has increased our understanding of this group of viruses. The future development of a safe and highly effective vaccine against rotavirus could prevent, at least, cases of severe diarrhea and reduce mortality from this disease.

Astrovirus, adenovirus, and rotavirus in hospitalized children: prevalence and association with gastroenteritis

BACKGROUND

Agents of viral gastroenteritis such as astrovirus, rotavirus, and adenovirus are common pediatric pathogens accounting for many physician visits, hospital admissions, and nosocomial infections. Previous hospital-based prevalence studies have examined mainly symptomatic children.

PURPOSE

To evaluate the prevalence of astrovirus, rotavirus, and adenovirus infections among hospitalized children less than 6 years of age, regardless of symptoms, and determine association with gastroenteritis.

METHODS

From September 1998 to June 2000, stool specimens were collected twice weekly from children less than five years of age admitted to two wards in a tertiary-care children's hospital. A total of 480 samples were obtained from 309 hospitalizations. Stools were examined using antibody-based ELISA for astrovirus, rotavirus, and adenovirus. Clinical data was abstracted from patient records.

RESULTS

Twenty one percent of the children had gastroenteritis symptoms at some point during their hospitalizations (43% were hospital acquired). Astrovirus was detected in 5.2% of all children compared to 6.8% with rotavirus and 0.8% with adenovirus serotypes 40 or 41. Nosocomial acquisition was common. Seventy five percent of astrovirus infections and 90% rotavirus infections were symptomatic. Astrovirus infections were significantly more likely to occur in younger infants and in children with compromised immunity. Rotavirus infections were significantly more likely to cause dehydration. In a three-year passive surveillance of gastroenteritis at the hospital, astrovirus and rotavirus infections peaked simultaneously in winter months.

CONCLUSIONS

Rotavirus and astrovirus are common symptomatic infections on pediatric wards and contribute greatly to inpatient morbidity. Adenoviruses played a limited role in gastroenteritis in hospitalized children in this study.

Molecular epidemiology of astrovirus infection in Barcelona, Spain

A 3-year study involving 2,347 gastroenteritis samples was conducted to determine the prevalence, time distribution, and medical significance of human astrovirus infection in Barcelona, Spain. The overall incidence of astrovirus was found to be 4.9%. Mixed infections with other enteric agents were detected in 17.2% of all astrovirus-positive samples. During the 3-year period, the highest astrovirus incidence was reported in the winter months, although infections also occurred in summer. The peak detection rate was observed in children between 2 and 4 years of age. Overall, HAstV-1 was the most prevalent type, followed by HAstV-4, HAstV-3, HAstV-8, and HAstV-2. HAstV-5, HAstV-6, and HAstV-7 were not detected during these 3 years. From our serotype data for each age group, we observed that HAstV-1, HAstV-2, and HAstV-3 affected mostly children younger than 3 years of age, while HAstV-4 and HAstV-8 had a greater impact in older children. Genetic variability was analyzed between astroviruses isolated in Barcelona and strains isolated in other parts of the world. A fourth lineage was described for HAstV-1, most likely due to the large number of assayed samples, which may also explain the high level of genetic variability observed in the astrovirus isolates.

An outbreak of gastroenteritis associated with astrovirus serotype 1 in a day care center, in Rio de Janeiro, Brazil

Between June 4th and June 20th 1996 rotavirus, adenovirus, and astrovirus (HAstrV) were investigated in fecal samples from 27 children under three years old with acute diarrhea, attending the Bertha Lutz day care center, in Rio de Janeiro. All fecal samples were analyzed by polyacrylamide gel electrophoresis (PAGE), reverse transcriptase polymerase chain reaction (RT-PCR), enzyme immunoassays (EIA), and electron microscopy (EM). Nine of them (33%) showed positive results for HAstrV by at least one of the employed methodologies. Eight were positive by RT-PCR and EIA, and six by EM. All positive samples were inoculated onto HT-29 (human colon adenocarcinoma) cultured cells for HAstrV isolation and seven were positive after three passages. The sequencing analysis of eight RT-PCR products (449 bp) from gene that codifies VP2 protein, showed a total nucleotide identity among them and 98% with HAstrV-1 (strain Oxford type 1). This is the first report of a gastroenteritis outbreak associated with HAstrv-1 in a day care center in Rio de Janeiro and it reinforces the importance of this virus in association with infantile acute gastroenteritis.

Genetic analysis of the capsid region of astroviruses

Eight serotypes of human astroviruses (HAstV-1 to HAstV-8) have been described. To date, the entire genomes of HAstV-1 and HAstV-2 as well as the ORF2 sequences of HAstV-1-6 and 8 have been reported. In this study, the ORF2 sequences of seventeen strains of HAstVs originating from different countries were determined, as well as the sequence ORF2 of one porcine astrovirus (PAstV) strain. Afterwards, comparison of the capsid protein precursors encoded by ORF2 of 46 strains of HAstVs, PAstV, and feline astrovirus (FAstV) was carried out. A phylogenetic tree showed eight genogroups of HAstVs that corresponded exactly to the serotypes. HAstV-3 and 7 were the most closely related, whereas HAstVs, FAstV, and PAstV segregated from each other. Compared to a PAstV, a FAstV is closer to HAstVs. Furthermore, the capsid protein precursors were divided into four regions (after amino acid residues 424, 688, and 776, respectively) based on sequence identity. Region I was the most conserved, and FAstV was very close in identity to HAstVs. Two amino acid motifs in region I were predicted to contain the common antigenic epitopes. Region II was relatively variable. Deletions and insertions were characteristic of region III, and region IV was relatively conserved. To our knowledge, this is the first comparative sequence analysis of the capsid protein precursors of eight serotypes of HAstVs as well as two animal astroviruses (FAstV and PAstV).

[Astrovirus infection in children with gastroenteritis]

OBJECTIVE

We report here a 2 year study (1997-1998) of astrovirus infection in children admitted to our hospital. The epidmioligical and clinical features of the infection were also investigated.

METHOD

A total of 1.815 stool specimens were tested during a two-year period (january 1997- december 1998). They were collected from children less than 3 years of age admitted to La Paz Hospital (Madrid) with acute gastroenteritis. We used a monoclonal antibody-based enzyme inmunoassay (IDEIA Astrovirus, DAKO) to detect astrovirus antigen in faecal samples.

RESULTS

Astroviruses were detected in 79 of the 1.815 analysed samples. This represented an incidence of 4,3%. The main symptom of infection was watery diarrhoea, and it was often associated with vomiting and fever. The majority of astrovirus infection occurred between the coldest months of the year. Children under a year of age were the most susceptible population. There was a considerable number of patients (62%) who develop the infection after 72 hours of admission.

CONCLUSION

The rate of detection reported here illustrates the importance of this pathogen in childhood diarrhoea, so we recommend its screening on a routine basis.

Ribovirus emergentes implicados en las gastroenteritis

Los virus se sitúan en un lugar preferente entre los agentes causales de diarrea aguda, en particular en la infancia. En este contexto el papel de los astrovirus, coronavirus, torovirus y picobirnavirus es emergente. Los astrovirus se han detectado en las heces entre el 1,2 y el 20 % de niños con diarrea que requieren atención médica en una gran variedad de localizaciones geográficas. Se han descrito brotes epidémicos en escuelas, guarderías y salas pediátricas, y son más frecuentes entre niños de menos de 3 años. En climas templados se ha demostrado una mayor incidencia invernal, y en climas tropicales ésta es similar en todo el año, siendo su transmisión preferente por vía orofecal. Se han reconocido siete serotipos de astrovirus humanos, de los cuales el más común es el uno. Los viriones pueden eliminarse durante amplios períodos y detectarse mediante microscopia electrónica. En estudios epidemiológicos se emplean técnicas de enzimoinmunoanálisis para detectar el antígeno común de grupo y se han desarrollado también técnicas basadas en la detección de ácidos nucleicos mediante hibridación y amplificación (reacción en cadena de la polimerasa).

Los coronavirus entéricos se han asociado con frecuencia con enfermedad gastrointestinal en recién nacidos y niños menores de 12 años. El papel de los torovirus y picobirnavirus como causa de gastroenteritis es también emergente. Se necesitan estudios epidemiológicos para determinar su verdadera frecuencia en la comunidad, identificar sus mecanismos de transmisión y explicar la fisiopatología de los cuadros provocados por estos agentes.

Molecular analysis of a serotype 8 human astrovirus genome

Human astroviruses are an important cause of gastroenteritis. As part of a molecular epidemiological study carried out in Mexico a human astrovirus isolate, Yuc-8, was adapted to grow in CaCo-2 cells, and its entire genome was sequenced. A 15 amino acid deletion in ORF1a, which has been associated with adaptation of astroviruses to grow in cells other than CaCo-2, was present in Yuc-8. Comparative sequence analysis of the Yuc-8 ORF2 with reported human astrovirus sequences revealed that this isolate belongs to genotype (serotype) 8. Two distinct domains in ORF2 were observed: an amino-terminal domain (residues 1 to 415), with identities higher than 81% among the strains analysed, and a carboxy-terminal domain (residues 416 to 782) with identities between 36 and 60%. Two non-superimposable phylogenetic trees were generated by separate analysis of these two domains, suggesting that a differential selective pressure is exerted along the structural polyprotein.

Identification and type distribution of astroviruses among children with gastroenteritis in Colombia and Venezuela

Astrovirus infections were detected by enzyme immunoassay in 12 (5%) of 251 stool samples from children with gastroenteritis from Bogota, Colombia. In addition, astroviruses were detected by reverse transcription-PCR in 3 (10%) of 29 stool samples negative for other enteric pathogens collected in Caracas, Venezuela, from children with gastroenteritis. Astrovirus type 1 was the most frequently detected virus.