Astrovirus MLB1 Research Articles

Detection of Novel Human Astrovirus MLB1 by a Commercial Viral Gastroenteritis Multiplex Assay

Detection of Novel Human Astrovirus MLB1 by a Commercial Viral Gastroenteritis Multiplex Assay

Multiple astrovirus MLB1, MLB2, VA2 clades, and classic human astrovirus in children with acute gastroenteritis in Japan.

This study investigated the genetic variability of astroviruses in children with acute gastroenteritis in Japan in 2012 to 2013. A total of 330 fecal specimens collected from children with diarrhea were tested for astroviruses using RT-PCR and nucleotide sequencing techniques. Among the tested specimens, 54 (16.4%) were positive for astrovirus. Three different phylogenetic clades were detected. MLB was the most predominant clade (35 samples), followed by classic astrovirus (17 samples), and VA astrovirus (2 samples). Two types of MLB were identified (MLB1 and MLB2), while classic astroviruses were HAstV1 and HAstV4. Two VA astroviruses were identified as VA2.

Prevalence of classic, MLB-clade and VA-clade Astroviruses in Kenya and The Gambia.

BackgroundInfectious diarrhea leads to significant mortality in children, with 40 % of these deaths occurring in Africa. Classic human astroviruses are a well-established etiology of diarrhea. In recent years, seven novel astroviruses have been discovered (MLB1, MLB2, MLB3, VA1/HMO-C, VA2/HMO-B, VA3/HMO-A, VA4); however, there have been few studies on their prevalence or potential association with diarrhea.MethodsTo investigate the prevalence and diversity of these classic and recently described astroviruses in a pediatric population, a case–control study was performed. Nine hundred and forty nine stools were previously collected from cases of moderate-to-severe diarrhea and matched controls of patients less than 5 years of age in Kenya and The Gambia. RT-PCR screening was performed using pan-astrovirus primers.ResultsAstroviruses were present in 9.9 % of all stool samples. MLB3 was the most common astrovirus with a prevalence of 2.6 %. Two subtypes of MLB3 were detected that varied based on location in Africa. In this case–control study, Astrovirus MLB1 was associated with diarrhea in Kenya, whereas Astrovirus MLB3 was associated with the control state in The Gambia. Classic human astrovirus was not associated with diarrhea in this study. Unexpectedly, astroviruses with high similarity to Canine Astrovirus and Avian Nephritis Virus 1 and 2 were also found in one case of diarrhea and two control stools respectively.ConclusionsAstroviruses including novel MLB- and VA-clade members are commonly found in pediatric stools in Kenya and The Gambia. The most recently discovered astrovirus, MLB3, was the most prevalent and was found more commonly in control stools in The Gambia, while astrovirus MLB1 was associated with diarrhea in Kenya. Furthermore, a distinct subtype of MLB3 was noted, as well as 3 unanticipated avian or canine astroviruses in the human stool samples. As a result of a broadly reactive PCR screen for astroviruses, new insight was gained regarding the epidemiology of astroviruses in Africa, where a large proportion of diarrheal morbidity and mortality occur.

Seroepidemiology of astrovirus MLB1.

To determine the seroprevalence of astrovirus MLB1 (MLB1), an indirect enzyme-linked immunosorbent assay (ELISA) was established. MLB1 seropositivity was high in children <6 months old, decreased to a nadir at 12 to 23 months old, and increased to 100% by adulthood. MLB1 infection is common, and primary exposure occurs in childhood.

Recently Identified Novel Human Astroviruses in Children with Diarrhea, China

Recently Identified Novel Human Astroviruses in Children with Diarrhea, China

Complete Genome Sequences of Two Astrovirus MLB1 Strains from Bhutanese Children with Diarrhea

In addition to the eight genotypes of classic human astroviruses, seven new genotypes have been reported from two novel clades, MLB and VA. However, the epidemiology of these highly diverse astroviruses remains largely unknown. We report here the complete genome sequences of two MLB1 strains from Bhutanese children with diarrhea.

Astrovirus MLB1 is not associated with diarrhea in a cohort of Indian children.

Astroviruses are a known cause of human diarrhea. Recently the highly divergent astrovirus MLB1 (MLB1) was identified in a stool sample from a patient with diarrhea. It has subsequently been detected in stool from individuals with and without diarrhea. To determine whether MLB1 is associated with diarrhea, we conducted a case control study of MLB1. In parallel, the prevalence of the classic human astroviruses (HAstVs) was also determined in the same case control cohort. 400 cases and 400 paired controls from a longitudinal birth cohort in Vellore, India were analyzed by RT-PCR. While HAstVs were associated with diarrhea (p = 0.029) in this cohort, MLB1 was not; 14 of the controls and 4 cases were positive for MLB1. Furthermore, MLB1 viral load did not differ significantly between the cases and controls. The role of MLB1 in human health still remains unknown and future studies are needed.

Detection of Newly Described Astrovirus MLB1 in Stool Samples from Children

To the Editor: We read with interest the article by Finkbeiner et al. describing an epidemiologic survey of newly described astrovirus MLB1 (AstV-MLB1) conducted in the United States in 2008 (1). This study was an extension of recently published reports of characterization of AstV-MLB1 from a fecal sample obtained in Australia in 1999 (2,3). These studies provide evidence of a divergent group of astroviruses and their etiologic association with human disease. However, the occurrence of a MLB1-like AstV in humans has already been documented. Walter identified a novel AstV in an 8-month-old child with diarrhea in Mexico in 1991 (4). In that study, Walter screened fecal samples for AstVs by using a variety of techniques. Sequencing of selected PCR products identified a unique virus that had typical AstV morphologic appearance but was nonreactive with human AstV-specific monoclonal or polyclonal antibodies. Phylogenetic analysis of fragments of open reading frame 1a (ORF1a) and ORF2 genome regions of this virus strain (M3363) showed that it was only distantly related to other mammalian AstVs, including human AstVs (4). This sequence divergence from canonical human AstVs suggested that M3363 might have been transmitted from an animal reservoir (4,5). When we reanalyzed ORF1a of M3363, we found that this strain was actually an MLB1-like AstV with >98% amino acid similarity to prototype and strains from the United States (Figure) that dated back to 1991. The fact that such closely related viruses were found in a scattered temporal and spatial pattern in children may indicate that MLB1-like AstVs represent a true human enteric virus, which was probably overlooked in the absence of adequate diagnostic reagents and protocols. Figure Neighbor-joining tree based on partial sequences of open reading frame 1a protein of human and animal astroviruses. Amino acid sequences of the Mexican M3363 strain (arrow) were obtained from Walter (4); other sequences were obtained from GenBank. Bootstrap ...

Detection of Newly Described Astrovirus MLB1 in Stool Samples from Children

To the Editor: We read with interest the article by Finkbeiner et al. describing an epidemiologic survey of newly described astrovirus MLB1 (AstV-MLB1) conducted in the United States in 2008 (1). This study was an extension of recently published reports of characterization of AstV-MLB1 from a fecal sample obtained in Australia in 1999 (2,3). These studies provide evidence of a divergent group of astroviruses and their etiologic association with human disease. However, the occurrence of a MLB1-like AstV in humans has already been documented. Walter identified a novel AstV in an 8-month-old child with diarrhea in Mexico in 1991 (4). In that study, Walter screened fecal samples for AstVs by using a variety of techniques. Sequencing of selected PCR products identified a unique virus that had typical AstV morphologic appearance but was nonreactive with human AstV-specific monoclonal or polyclonal antibodies. Phylogenetic analysis of fragments of open reading frame 1a (ORF1a) and ORF2 genome regions of this virus strain (M3363) showed that it was only distantly related to other mammalian AstVs, including human AstVs (4). This sequence divergence from canonical human AstVs suggested that M3363 might have been transmitted from an animal reservoir (4,5). When we reanalyzed ORF1a of M3363, we found that this strain was actually an MLB1-like AstV with >98% amino acid similarity to prototype and strains from the United States (Figure) that dated back to 1991. The fact that such closely related viruses were found in a scattered temporal and spatial pattern in children may indicate that MLB1-like AstVs represent a true human enteric virus, which was probably overlooked in the absence of adequate diagnostic reagents and protocols. Figure Neighbor-joining tree based on partial sequences of open reading frame 1a protein of human and animal astroviruses. Amino acid sequences of the Mexican M3363 strain (arrow) were obtained from Walter (4); other sequences were obtained from GenBank. Bootstrap ...

Human stool contains a previously unrecognized diversity of novel astroviruses

Human astroviruses are a leading cause of gastrointestinal disease. Since their discovery in 1975, 8 closely related serotypes have been described in humans, and more recently, two new astrovirus species, astrovirus MLB1 and astrovirus VA1, were identified in diarrhea patients. In this study, we used consensus astrovirus primers targeting the RNA polymerase to define the diversity of astroviruses present in pediatric patients with diarrhea on two continents. From 416 stool specimens comprising two different cohorts from Vellore, India, 35 samples were positive. These positive samples were analyzed further by either sequencing of the ~400 bp amplicon generated by the consensus PCR or by performing additional RT-PCR specific for individual astroviruses. 19 samples contained the classic human astrovirus serotypes 1-8 while 7 samples were positive for the recently described astrovirus MLB1. Strikingly, from samples that were positive in the consensus PCR screen but negative in the specific PCR assays, five samples contained sequences that were highly divergent from all previously described astroviruses. Sequence analysis suggested that three novel astroviruses, tentatively named astroviruses VA2, MLB2 and VA3, were present in these five patient specimens (AstV-VA2 in 2 patients, AstV-MLB2 in 2 patients and AstV-VA3 in one patient). Using the same RT-PCR screening strategy, 13 samples out of 466 tested stool specimens collected in St. Louis, USA were positive. Nine samples were positive for the classic human astroviruses. One sample was positive for AstV-VA2, and 3 samples were positive for AstV-MLB2 demonstrating that these two viruses are globally widespread. Collectively, these findings underscore the tremendous diversity of astroviruses present in fecal specimens from diarrhea patients. Given that a significant fraction of diarrhea etiologies is currently unknown, it is plausible that these or other yet unrecognized astroviruses may be responsible for at least part of the undiagnosed cases.

Detection of Newly Described Astrovirus MLB1 in Stool Samples from Children

The prevalence of the recently identified astrovirus MLB1 in a cohort of children with diarrhea in St. Louis, Missouri, USA, was defined by reverse transcription–PCR. Of 254 stool specimens collected in 2008, 4 were positive for astrovirus MLB1. These results show that astrovirus MLB1 is circulating in North America.

Detection of Newly Described Astrovirus MLB1 in Stool Samples from Children

The prevalence of the recently identified astrovirus MLB1 in a cohort of children with diarrhea in St. Louis, Missouri, USA, was defined by reverse transcription-PCR. Of 254 stool specimens collected in 2008, 4 were positive for astrovirus MLB1. These results show that astrovirus MLB1 is circulating in North America.

Complete genome sequence of a highly divergent astrovirus isolated from a child with acute diarrhea

BackgroundAstroviruses infect a variety of mammals and birds and are causative agents of diarrhea in humans and other animal hosts. We have previously described the identification of several sequence fragments with limited sequence identity to known astroviruses in a stool specimen obtained from a child with acute diarrhea, suggesting that a novel virus was present.ResultsIn this study, the complete genome of this novel virus isolate was sequenced and analyzed. The overall genome organization of this virus paralleled that of known astroviruses, with 3 open reading frames identified. Phylogenetic analysis of the ORFs indicated that this virus is highly divergent from all previously described animal and human astroviruses. Molecular features that are highly conserved in human serotypes 1–8, such as a 3'NTR stem-loop structure and conserved nucleotide motifs present in the 5'NTR and ORF1b/2 junction, were either absent or only partially conserved in this novel virus.ConclusionBased on the analyses described herein, we propose that this newly discovered virus represents a novel species in the family Astroviridae. It has tentatively been named Astrovirus MLB1.