Molecular epidemiology of human astrovirus diarrhea among children from a periurban community of Mexico City

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.

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.

Prevalence and characterization of astroviruses in Argentinean children with acute gastroenteritis

Among viral agents causing gastroenteritis, human astroviruses (HAstVs) take second or third place, after rotaviruses and caliciviruses, as the most frequent cause of illness. The aims of this study were to determine the prevalence of HAstV infection and to characterize the circulating HAstV strains in children with diarrhea under 3 years of age treated between 1995 and 1998 at out- or in-patient facilities of the children's hospital in Mendoza, Argentina. Reverse transcription-polymerase chain reaction (RT-PCR) and enzyme immunoassay (EIA) were used to detect HAstVs in stool specimens. Positive specimens were tested further by EIA and/or sequenced to type detected HAstV strains. HAstVs were detected in 40 (3.7%) of 1,070 samples that were rotavirus and calicivirus-negative: 14 (3.5%) of 402 from outpatients and 26 (3.9%) of 668 from inpatients. HAstV infection tended to be more severe in children during their first year of life: 18 (4.7%) of 383 HAstV-positive children 0-11 months old were hospitalized versus 8 (2.8%) of 285 children 1 year of age or older (P = 0.29). Type 1 (HAstV-1) was the most common type (41%), followed by HAstV-4 (25%), HAstV-2 (13%), HAstV-3 (13%), and HAstV-5 (8%). In this first epidemiological study of HAstV infection in this region, we confirmed HAstV to be a cause of severe gastroenteritis in children, more often among children younger than 12 months of age. HastV-4 caused 25% of HastV infections in Mendoza, although it has been detected commonly elsewhere. Distinct genetic lineages were apparent but their epidemiological significance remains to be demonstrated.

Molecular characterization and sequence analysis of human astroviruses circulating in Hungary

Human astroviruses (HAstVs) are major pathogens in viral gastroenteritis worldwide. Twenty-five HAstV strains were detected from stool specimens of children hospitalized for acute gastroenteritis in Budapest, Hungary, between 1995 and 1999. Sequence analysis was performed at the 3' end of the capsid gene to determine genotypic diversity of HAstVs circulating in Hungary. Five different genotypes of HAstVs were identified: HAstV-1 was predominant, followed by types 5, 8, 3 and 4. Two different subtypes of HAstV-1 were detected, but only one at a time in the community. This is the first report on the genetic diversity of HAstVs in Hungary and Central/Eastern Europe.

Viral agents of acute gastroenteritis in German children: prevalence and molecular diversity

Acute gastroenteritis is a major source of morbidity and mortality among young children in developed and developing countries. Enteropathogenic viruses are regarded as particularly relevant causative agents. Between February 2001 and January 2002, fecal specimens were obtained from German children admitted to hospital with acute gastroenteritis and examined for rotaviruses, Noroviruses, enteric adenoviruses, and astroviruses using (RT-)PCR methods. Of the 59% (129/217) samples positive for > or =1 viral agent, 79% (102/129) carried rotavirus, whereas Norovirus was detected in 35% (45/129), enteric adenovirus in 14% (18/129), and astrovirus in 4% (5/129). Thirty-eight specimens contained at least two enteropathogenic viruses, with the majority of coinfections attributable to rotavirus/Norovirus dual infections. Sequence analysis revealed a cocirculation of G1, G3, G4, and G9 type rotavirus with G1 being the most common and G9 the second most common rotavirus G-type. Emergence of G9 rotaviruses in Germany may have implications for future vaccine development. A variety of Norovirus genotypes, most belonging to GGII, were found. Apart from subgenus F, adenovirus related genetically to subgenera A-C were detected. All astroviruses belonged to genotype 1. This is the first study concerning German children admitted to hospital that assesses the relative importance of these viruses by nested (RT-) PCR methods.

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.

Astrovirus infection in children

PURPOSE OF REVIEW

Public health concerns related to enteric viral agents, such as astroviruses and caliciviruses, include their ability to cause sporadic diarrhea, large outbreaks of gastroenteritis, and hospitalizations or deaths resulting from vomiting, diarrhea, and dehydration. Improved surveillance and application of sensitive molecular assays has increased awareness of these enteric pathogens and reduced the 'diagnostic gap' or unknown causes of non-bacterial gastroenteritis.

RECENT FINDINGS

Molecular assays have been applied to further describe the epidemiology of human astroviruses from a variety of geographic areas. The burden of astrovirus infections compared with other enteric viral agents, including rotaviruses, caliciviruses, and enteric adenoviruses have been reported. New methods for detection of astroviruses such as reverse transcription-polymerase chain reaction and molecular typing methods have advanced the understanding of the epidemiology. Additional molecular studies have described the protein processing mechanisms of this single-stranded RNA virus.

SUMMARY

Astroviruses are increasingly recognized as significant gastrointestinal pathogens. The understanding of molecular epidemiology and molecular processing of the virus may lead to specific prevention strategies.

Are waterborne astrovirus implicated in acute digestive morbidity (E.MI.R.A. study)?

BACKGROUND

With rotavirus and Norwalk-like viruses, astroviruses are now recognized as important etiologic agents of viral gastroenteritis in all age groups. However, astrovirus is neither routinely screened for in stool samples, nor in environmental samples, and data on the health impact of waterborne astrovirus are lacking.

OBJECTIVES

To assess the potential impact of astrovirus in drinking water on the incidence of acute digestive conditions (ADC) among a panel of volunteers.

STUDY DESIGN

The Epidemiology and MIcrobial Risk Assessment (E.MI.R.A.) study combined a daily epidemiological follow-up of digestive morbidity among a panel of 544 volunteers supplied by French public water systems, and a microbiological surveillance of drinking water. Cases of digestive morbidity were collected through weekly telephone calls. The bacterial, virological and parasitic quality of tap water was assessed monthly. Additional samples were collected if the incidence of ADC increased. The relationship between incidence of ADC during a 7-day period centered about the water sampling day and astrovirus RNA prevalence in drinking water was modeled by regression techniques, taking into account several confounders.

RESULTS

12% (8/68) of the analyzed water samples were positive for astrovirus, and presence of astrovirus RNA was associated with a significant increased risk of ADC: RR=1.51 (95% CI=[1.17-1.94], P value=0.002).

CONCLUSIONS

This result suggests a role for waterborne astrovirus in the endemic level of digestive morbidity in the general population. Perhaps astrovirus is a candidate test target for viral surveillance of drinking water.

Molecular characterization of astroviruses by reverse transcriptase PCR and sequence analysis: comparison of clinical and environmental isolates from South Africa

A comparative analysis was performed with 25 isolates of astroviruses (AstVs) detected in sewage sources and 22 concurrently identified clinical AstV isolates from the Tshwane (Pretoria) Metropolitan Area in South Africa. The samples and specimens were screened for AstVs by using an enzyme immunoassay and/or a reverse transcriptase PCR (RT-PCR) for the highly conserved untranslated region (3' end) of the genome. The RT-PCR results were confirmed by oligonucleotide probe dot blot hybridization. Viable viruses were propagated in cell cultures for amplification when a minimal specimen was available or indeterminate sequences were obtained. AstV strains were characterized by RT-PCR and partial sequence analysis of the capsid region. The presence of multiple human AstV (HAstV) types in a single sewage sample complicated identification of individual strains, and additional type-specific RT-PCR and sequence analyses of the capsid region were required for characterization. Amplification and characterization of one genotype from a sample, therefore, did not preclude the possibility that a sample harbored additional different genotypes. Genotype and sequence information obtained from AstVs in wastewater samples were compared to information obtained from AstV strains from human stools. HAstV type 1 (HAstV-1), as well as HAstV-3, -5, -6, and -8, were identified among the clinical isolates, and HAstV-1, -2, -3, -4, -5, -7, and -8 were identified among the environmental samples. Phylogenetic analysis demonstrated that HAstV-1, -3, -5, and -8, which were present in human stool and sewage samples, clustered together, indicating that these viruses are closely related. The concurrent presence of identical HAstV strains in wastewater samples and in hospitalized patients suggests that AstVs present in the environment pose a potential risk to communities in which fecally contaminated water is used for recreational and domestic purposes.

Astrovirus acute gastroenteritis among children in Madrid, Spain

BACKGROUND

Human astroviruses cause infantile gastroenteritis worldwide, but the prevalence of disease varies greatly by setting. Since 1997 we have conducted a survey to determine the causes of diarrhea among Spanish children attending an emergency room in Madrid and to characterize the clinical features of viral-associated gastroenteritis.

OBJECTIVES

To define the epidemiologic role of astrovirus-associated gastroenteritis in Spanish children, to review its clinical features and to compare these illnesses with those caused by rotavirus. To assess the sensitivity of two methods of detection [enzyme-linked immunosorbent assay (EIA) and reverse transcriptase (RT)-PCR].

METHODS

Fecal specimens from 822 children with acute diarrhea treated at an emergency room were screened by EIA assays. Random astrovirus-positive samples were characterized by RT-PCR and nucleotide sequencing for their phylogenetic grouping.

RESULTS

Astrovirus was detected in 44 (5.3%) of 822 specimens tested by EIA. No pathogens were detected in fecal specimens from 238 (29%) children; however, in 137 of those with adequate remaining specimens, we found an additional 50 (6.1%) that were positive by RT-PCR. HAstV-1 was the most prevalent type followed by HAstV-2. The gastroenteritis associated with astrovirus alone was slightly less severe and had a lower score or risk of hospitalization than that associated with rotavirus (P < 0.05).

CONCLUSIONS

Astrovirus was found in 11.4% of all children whom we tested for enteric viral and bacterial pathogens, making it the second most common cause of acute gastroenteritis among Spanish children. True prevalence of astrovirus could be underestimated if only EIAs were used for detection.

Detection and characterisation of human astroviruses in children with acute gastroenteritis in Blantyre, Malawi

In a 2-year hospital-based study of paediatric gastroenteritis in Blantyre, Malawi, astroviruses were detected by enzyme immunoassay in 15 (1.9%) of 786 inpatients and in 9 (2.3%) of 400 outpatients. Greater disease severity was noted in children coinfected with human immunodeficiency virus (HIV). Six human astrovirus (HAstV) genotypes were identified, including HAstV-1 (25%), HAstV-2 (21%), HAstV-3 (25%), HAstV-4 (13%), HAstV-5 (4%), and HAstV-8 (13%). Although astroviruses are not major causes of gastroenteritis among children admitted to hospital in Blantyre, concomitant HIV infection appears to be a risk factor for increased severity of disease.

Evolutionary relationships among Astroviridae

To study the evolutionary relationships among astroviruses, all available sequences for members of the family Astroviridae were collected. Phylogenetic analysis distinguished two deep-rooted groups: one comprising mammalian astroviruses, with ovine astrovirus being an outlier, and the other comprising avian astroviruses. All virus species as well as serotypes of human astroviruses represented individual lineages within the tree. All human viruses clustered together and separately from non-human viruses, which argue for their common evolutionary origin and against ongoing animal-to-human transmissions. The branching order of mammalian astroviruses was exactly the opposite of that of their host species, suggesting at least two cross-species transmissions involving pigs, cats and humans, possibly through intermediate hosts. Analysis of synonymous (Ds) versus non-synonymous (Da) distances revealed that negative selection is dominating in the evolution of astroviruses, with the Ds:Da ratios being up to 46 for the comparisons of the most closely related viruses. Phylogenetic analyses of all open reading frames (ORFs) based on Ds resulted in the loss of tree structures, with virus species--and in ORF2, even serotypes of human astroviruses--branching out from virtually a single node, suggesting their ancient separation. The strong selection against non-synonymous substitutions, the low number of which is, therefore, not proof of a recent separation between lineages, together with the position of the oldest available human astrovirus strain (1971) far from the common node of its serotype 4, suggest that intraserotype diversification originates from an earlier date.