Astrovirus VA2 (AstV‑VA2), also known as HMO‑A, is a human astrovirus genotype classified within the VA clade of the family Astroviridae. It is a non‑enveloped, positive‑sense single‑stranded RNA virus with a star‑shaped icosahedral capsid. VA2 is genetically distinct from the classic human astrovirus serotypes and from the other VA clade members such as VA1 and VA3.
Explanation
Astrovirus VA2 shares the general structural and genomic features of other astroviruses: virions are about 28‑30 nm in diameter and harbor a positive‑sense RNA genome of approximately 6.4–7.7 kb encoding non‑structural proteins and a capsid protein. VA2 was first detected by broad‑range PCR in stool specimens from children and adults and has since been reported in samples from the United States, Egypt, India and Nigeria. Phylogenetically, it clusters within the VA clade of mammalian astroviruses and is distinct from the MLB clade. The epidemiology and clinical significance of VA2 remain poorly defined. Available data indicate that VA2 can be found in both symptomatic and asymptomatic individuals, and there is no clear association with diarrhoeal illness. The virus is presumed to be transmitted via the fecal‑oral route, as for other astroviruses, and is stable under environmental conditions. Because of its genetic divergence, detection requires pan‑astrovirus PCR or sequencing rather than assays designed for the classic serotypes. Serological data for VA2 are limited, but cross‑reactive antibodies to other VA viruses suggest that exposure may be widespread.
Current observations
VA2 has been detected sporadically on multiple continents. In surveillance studies it has been identified in stool samples from healthy individuals as well as from patients with gastroenteritis, but no consistent link to disease has been established. The geographical range of VA2, including reports from the United States, Egypt, India and Nigeria, suggests that the virus circulates globally at low levels. The absence of well‑documented outbreaks or severe cases implies that VA2 infections are often mild or asymptomatic. Astrovirus VA2 is a genetically distinct human astrovirus genotype whose clinical impact is still uncertain. Ongoing monitoring and serological surveys are needed to elucidate its prevalence and potential role in human disease. Related Terms: Astrovirus VA1, Astrovirus VA3, Astrovirus VA4, Astrovirus MLB2, Human Astrovirus 2