INTRODUCTION

Family: Astroviridae

Genus: Astrovirus

Species: Human astrovirus 1-8

Diarrhea is still a major cause of mortality worldwide, and the highest incidence of diarrhea-related death occurs in developing nations . Astroviruses are one of several viruses (including caliciviruses and rotaviruses) which can cause gastroenteritis. Astroviruses were first observed in the feces of children in 1975 through electron microscopy, and they are UBIQUITOUS among young children. They are the second most common cause, after rotavirus, of viral diarrhea in Thailand and Guatemala.

Basic properties of human astroviruses:

• * Initially appears to resemble picornavirus, but when viewed from a certain angle, viral particles viewed by electron microscopy reveal a smooth or slightly indented outer electron-dense shell with a negatively staining 5 or 6 pointed star-like inner core.
• * Naked virions are spherical and 28-30 nm in diameter.
• * Viral genome consists of a single, linear RNA 7.2-7.9 kb molecule that is single-stranded, positive sense, and is polyadenylated at the 3' end.
• * Replication occurs in cell cytoplasm. ·
• * Two or three different proteins comprise the icosahedral capsid.
• * Mature virions are often observed in crystalline arrays in the cell cytoplasm.
• * Virions are hardy, for they are relatively resistant to heat and acidity.