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 ...

Untreated sewage samples from 12 cities in the United States were screened for the presence of recently characterized RNA and DNA viruses found at high prevalence in the stool specimens of South Asian children. Genetic variants of human cosaviruses and cardioviruses in the Picornaviridae family and of DNA circoviruses and human bocaviruses were detected, expanding the known genetic diversity and geographic range of these newly identified viruses. All four virus groups were detected in sewage samples of less than a milliliter from multiple U.S. cities. PCR screening of particle-protected viral nucleic acid in sewage samples could therefore rapidly establish the presence and determine the diversity of four newly described enteric viruses in large urban populations. More frequent and deeper sampling of viral nucleic acids in sewage samples could be used to monitor changes in the prevalence and genetic composition of these and other novel enteric viruses.

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