Astrovirus VA3 (AstV‑VA3), also called HMO‑B, is a genotype of human astrovirus belonging to the VA clade in the family Astroviridae. It is a non‑enveloped, positive‑sense single‑stranded RNA virus with an icosahedral capsid that displays a star‑like surface under electron microscopy. VA3 is genetically distinct from both the classic human astrovirus serotypes and from other members of the VA and MLB lineages.
Explanation
Astrovirus VA3 shares structural and genomic characteristics with other astroviruses: its particles measure about 28‑30 nm and contain a positive‑sense RNA genome of around 6.4–7.7 kb encoding non‑structural proteins and a capsid protein. VA3 was identified through metagenomic analyses of stool samples and has been reported primarily in India and Pakistan. Phylogenetic analyses place VA3 within the VA clade, yet it is distinct from VA1 and VA2. To date there are few epidemiological data on VA3; it has been detected in both diarrhoeal and non‑diarrhoeal specimens, but its association with disease is uncertain. The virus is thought to spread via the fecal–oral route. Because of its genetic divergence, detection of VA3 relies on pan‑astrovirus PCR assays and sequencing rather than tests designed for the classic serotypes.
Key points
Reports of VA3 are limited to a small number of studies. Surveys of stool samples from Indian and Pakistani children have identified VA3 sequences, but the virus has not been linked to any specific clinical syndrome. No outbreaks or severe cases have been attributed to VA3. The absence of serological data means that the prevalence of VA3 infections in the general population remains unknown.
Astrovirus VA3 is a poorly characterized human astrovirus genotype that appears to circulate at low levels. Ongoing molecular surveillance in diverse populations is necessary to determine its distribution and whether it plays a role in human illness.
Related Terms: Astrovirus VA1, Astrovirus VA2, Astrovirus VA4, Astrovirus MLB3, Human Astrovirus 3