Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Molecular Microbiology and Microbial Pathogenesis


English (en)

Date of Award

January 2009

Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

David Wang


Approximately 1.8 million children die from diarrhea annually, and millions more suffer multiple episodes of nonfatal diarrhea. Despite the availability of improved molecular diagnostics to detect the known viral agents, the etiology of a large proportion of diarrheal cases is unknown. In fact, it is estimated that no causative agent can be identified in up to 40% of sporadic cases or in gastroenteritis outbreaks. Detection of novel or unexpected viruses is the first step in identifying agents that could potentially close the diagnostic gap and pave the way for the development of more comprehensive preventative measures and better treatments. This dissertation encompasses the first application of cutting edge mass sequencing approaches to the analysis of viruses present in fecal specimens from patients with diarrhea. Known enteric viruses as well as multiple sequences: with only limited sequence similarity to viruses in GenBank) from putatively novel viruses were detected in pediatric sporadic diarrhea specimens. One virus, Astrovirus MLB1: AstV-MLB1), was fully sequenced and determined to be a highly divergent, novel astrovirus based on phylogenetic analysis. AstV-MLB1 was further detected by RT-PCR in 4/254 fecal specimens collected at the St. Louis Children's hospital in 2008, indicating that AstV-MLB1 is currently circulating in North America. A second highly divergent, novel astrovirus, Astrovirus VA1: AstV-VA1), was identified in two specimens from a gastroenteritis outbreak at a child care center. Mass sequencing yielded nearly the entire genome of AstV-VA1 which appears to be most closely related to astroviruses found in mink and sheep. One additional sample also tested positive for AstV-VA1 by RT-PCR, resulting in detection of the virus in 3/5 specimens collected from the outbreak. This presents the possibility that further investigations might reveal that AstV-VA1 is a causative agent of gastroenteritis outbreaks. The identification of two novel astroviruses in fecal specimens from children with diarrhea suggests that astroviruses may cause a larger fraction of diarrhea cases than previously recognized. Furthermore, the identification and characterization of novel astroviruses MLB1 and VA1 lays the foundation for future investigations into their potential roles as etiologic agents of diarrhea.


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