Caliciviridae and Astroviridae

Caliciviruses Associated with Gastroenteritis 407

Hepatitis E Virus 411

Astroviruses 415 1

Further Reading 417

Although it had been recognized for many years that gastroenteritis could be transmitted to human volunteers by ingestion of bacteria-free filtrates of feces from patients with diarrhea, it was not until 1972 that the first of the many types of viruses involved was identified, by immunoelectron microscopy (IEM). Nofwalk virus, named for the town in Ohio that hosted the outbreak yielding the virus, was the prototype of a succession of "small round-structured viruses" whose taxonomic status remained unclear until 1991 when sequencing of the genome made it apparent that they belong to the family Caliciviridae. Caliciviruses had been well known for years to veterinary virologists interested in such major animal pathogens as vesicular exanthema of swine virus and feline calicivirus. In 1991 the genome of the noncultivable agent of another important enterically transmitted disease, hepatitis E, was cloned and sequenced, and the virus was provisionally classified as a member of the family Caliciviridae.

In addition, electron microscopists had described virions from gastroenteritis outbreaks in animals or humans which looked somewhat different in that they presented a distinct star-shaped outline (Fig. 24-1B). In 1993 these "astroviruses" were accorded the status of a separate family, Astroviridae

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