Multiple novel astrovirus species in human stool

Abstract

Diarrhoea remains a significant cause of morbidity and mortality in developing countries where numerous cases remain without identified aetiology. Astroviruses are a recently identified cause of animal gastroenteritis which currently includes two species suspected of causing human diarrhoea. Using pan-astrovirus RT-PCR, we analysed human stool samples from different continents for astrovirus-related RNA sequences. We identified variants of the two known human astrovirus species plus, based on genetic distance criteria, three novel astrovirus species all distantly related to mink and ovine astroviruses, which we provisionally named HMOAstV species A-C. The complete genome of species A displayed all the conserved characteristics of mammalian astroviruses. Each of the now three groups of astroviruses found in human stool (HAstV, AstV-MLB and HMOAstV) were more closely related to animal astroviruses than to each other, indicating that human astroviruses may periodically emerge from zoonotic transmissions. Based on the pathogenic impact of their closest phylogenetic relatives in animals, further investigations of the role of HMOAstV, so far detected in Nigeria, Nepal and Pakistan, in human gastroenteritis are warranted. INTRODUCTIONThe family Astroviridae consists of small (28-30 nm in diameter), non-lipid enveloped, single-stranded positivesense RNA viruses whose genomes range in size from 6.4 to 7.3 kb. The genome includes three open reading frames (ORFs) designated ORF1a, ORF1b and ORF2. ORF1a encodes the non-structural polyprotein 1a while the longer ORF1b encodes polyprotein 1ab including the RNA dependent RNA polymerase (RdRp) expressed through a ribosomal frameshift at the ORF1a/1b junction mediated by a slippery polyA sequence. ORF2 encodes the viral capsid structural polyprotein (Mendéz & Arias, 2007; Monroe et al., 2005).The family Astroviridae consists, so far, of two genera, Avastrovirus and Mamastrovirus, that infect avian and mammalian hosts, respectively. Astroviruses, transmitted through the faecal-oral route can cause gastroenteritis in mammalian and avian species, including humans, calves, piglets, sheep, minks, dogs, cats, mice, chickens and turkeys (Jonassen et al., 2001(Jonassen et al., , 2003. All eight known human astrovirus serotypes belonging to the first identified human astrovirus species (HAstV) have been associated with gastroenteritis (Clark & McKendrick, 2004;Fodha et al., 2006; Gabbay et al., 2007;Jin et al., 2009; Tayeb et al., 2008). Clinical symptoms of HAstV infection in humans usually last between 2 and 4 days and consist of watery diarrhoea and, less commonly, vomiting, headache, fever, abdominal pains and anorexia (Mendéz & Arias, 2007; Monroe et al., 2005). HAstV can also cause significant disease in the elderly and in immunocompromised patients (Liste et al., 2000). Recently, a second species of astrovirus was found in a child with diarrhoea and named AstV-MLB (Finkbeiner et al., 2008).Group-reactive or pan-PCR approaches have been used successfully to identify new viruses ...

Wastewater Analysis Indicates that Genetically Diverse Astroviruses, Including Strains Belonging to Novel Clades MLB and VA, Are Circulating within Japanese Populations

“…Similarly, clinical studies investigating infantile diarrheal samples in India, the United States, Egypt, and China reported the more frequent occurrence of MLB-AstVs than VA-AstVs (22,49,50). A previous clinical study reported the less frequent detection of MLB-AstV, but the study investigated samples from adults with diarrhea and children without diarrhea (20). These observations suggest that MLB-AstVs may be more prevalent than VA-AstVs among children with diarrheal disease.…”

“…The presence of these novel AstVs has been documented in several countries, including Australia, China, India, Nepal, the Netherlands, Nigeria, Pakistan, and the United States, but not in Japan (19,20,22,23,47,48). We identified MLB-AstVs in all influent samples collected between November 2007 and March 2008.…”

“…The novel AstV strains are genetically distinct from the classic HAstV strains (20)(21)(22); in fact, VA-AstVs are genetically more closely related to mink/ovine AstVs than to classic HAstVs (20,22). To date, MLB-AstVs have been divided into 3 genotypes (MLB-AstV genotype 1 [MLB-AstV-1] to MLB-AstV-3) and VAAstVs have been divided into 4 genotypes (VA-AstV genotype 1 [VA-AstV-1] to VA-AstV-4) (7,20,23,24). It has been suggested that VA-AstV-1 and MLB-AstV-1 are associated with gastroenteritis outbreaks (23,25), but the prevalence and etiological role of the novel AstV strains in humans remain unclear (26,27).…”

“…In spite of their importance as enteric pathogens, the occurrence and other characteristics of HAstVs in water compared to those of other enteric viruses, such as noroviruses, rotaviruses, and adenoviruses, have not been well documented (17, 18). Due to the scarcity of knowledge, the fate of HAstVs in water environments and wastewater treatment processes is not well understood.Recent studies based on viral metagenomic analysis have identified some novel AstVs, namely, clade MLB AstVs (MLB-AstVs) and clade VA (HMO) AstVs (VA-AstVs), in human feces (19,20). The novel AstV strains are genetically distinct from the classic HAstV strains (20)(21)(22); in fact, VA-AstVs are genetically more closely related to mink/ovine AstVs than to classic HAstVs (20,22).…”

“…Recent studies based on viral metagenomic analysis have identified some novel AstVs, namely, clade MLB AstVs (MLB-AstVs) and clade VA (HMO) AstVs (VA-AstVs), in human feces (19,20). The novel AstV strains are genetically distinct from the classic HAstV strains (20)(21)(22); in fact, VA-AstVs are genetically more closely related to mink/ovine AstVs than to classic HAstVs (20,22).…”