Astrovirus - Classification, Characteristics, Morphology, Genome

Classification of Astrovirus

Realm: Riboviria

Kingdom: Orthornavirae

Phylum: Pisuviricota

Class: Stelpaviricetes

Order: Stellavirales

Family: Astroviridae

Medically important genera are: Avastrovirus, Mamastrovirus

Introduction to Astrovirus

Astrovirus is a common cause of diarrhoeal disease transmitted worldwide by the fecal-oral route and fomites. The very young and elderly individuals are most at risk and may require rehydration while

prolonged excretion occurs in an immunocompromised host.

Cold foods and shellfish harvested from contaminated water are important sources of infection. Astrovirus has been associated with extensive outbreaks of food-borne infection in Japan. It contains two genera: the Mamastrovirus – which infects animals and Aviastrovirus- which infects birds.

Morphology of Astrovirus

Astrovirus is recognized by 5 or 6 pointed stars on their surface (Greek: Astron = star). Morphological studies of astrovirus have confirmed that it has a diameter of 28-35 nm and is surrounded by a hair-like fringe. It is non-enveloped with icosahedral symmetry and its capsid is composed of 2 or 3 structural proteins.

Genome of Astrovirus

The viral genome is positive single-stranded RNA, which is linear and is 6.8-7.9kb. RNA has a poly (A) tract at the 3’-terminus but is not capped in the 5’-end. The genome encodes 3 ORFs- 1a, 1b and 2

• ORF1a = encodes transmembrane helices (MB), 3C-like serine protease (Pro), and nuclear localization signal (NLS)

• ORF 1b = encodes an RNA-dependent RNA polymerase (Pol)

• ORF 2 = encodes a 79 kDa structural polyprotein which is cleaved by cellular proteases to generate the viral capsid proteins- VP34, VP29, and VP26

A 70-nucleoside region between ORF1a and ORF1b is highly conserved and contains a signal and downstream stem-loop structure indicative of ribosomal frameshifting. Eight genotypes and antigenic strains of Astroviruses are present.

Arenavirus in short