Astroviridae is one of the most recently designed virus families whose members include human and animal astroviruses.  These viruses are small in size and icosahedral in shape, and they are named after their characteristic starlike surface structure (astron is Greek for "star").  They are nonenveloped viruses whose genome is composed of positive-sense, single-stranded RNA.  Although they are very similar to the viruses of the family Picornaviridae and Caliciviridae, they have many important features that distinguish themselves.
    Astroviruses have been isolated from humans as well as many other animal species.  In most species, the astroviruses cause gastroenteritis; however, in ducklings, astrovirus infection causes a fatal hepatitis.  In humans, astrovirus was recently found to be the second most common cause (after rotavirus) of viral diarrhea in young children in Thailand and Guatemala, establishing medical importance to astrovirus infection.