Astrovirus VA1 (AstV‑VA1), also known as HMO‑C, is a genotype of human astrovirus in the VA clade of the family Astroviridae. It is a non‑enveloped, positive‑sense single‑stranded RNA virus that forms an icosahedral capsid with a star‑like appearance. VA1 is phylogenetically distinct from the eight classic human astrovirus serotypes and from the MLB genotypes, sharing closer similarity with some animal astroviruses.
Explanation
Like other astroviruses, VA1 particles measure around 28‑30 nm and contain a positive‑sense RNA genome of approximately 6.4–7.7 kilobases that encodes non‑structural proteins (ORF1a and ORF1b) and the capsid protein (ORF2). VA1 was discovered by metagenomic analysis of stool samples from children in the United States and was later detected in stool collections from Nepal and the Netherlands. Phylogenetic analysis revealed that VA1 forms a distinct lineage, now classified as Mamastrovirus 9. Epidemiological studies suggest that VA1 is common in human populations; a serosurvey found antibodies to VA1/HMO‑C in about 65 % of adults and 20–36 % of children, indicating widespread exposure. Unlike the classic astroviruses that primarily cause diarrhea, VA1 has been found in both symptomatic and asymptomatic individuals, and its role in disease is unclear. The virus is stable in the environment, is transmitted via the fecal–oral route and resists heat and acid. Diagnostic detection requires broad‑range astrovirus PCR or sequencing because of its genetic divergence.
Notable findings
VA1 has been detected in stool samples from multiple continents. A particularly notable observation involved a VA1‑related astrovirus (astrovirus‑PS) isolated from the brain tissue of a four‑year‑old boy with fatal encephalitis, suggesting that members of the VA clade may have neurotropic potential. However, the majority of infections appear to be mild or asymptomatic, and no outbreaks have been definitively linked to VA1. Seroprevalence data showing widespread immunity support the idea that this virus circulates silently in human populations.
Astrovirus VA1 is a divergent human astrovirus genotype that seems to infect people globally with little or no symptoms. Additional surveillance, especially of neurological cases, is required to understand its full clinical spectrum and transmission dynamics.
Related Terms: Astrovirus VA2, Astrovirus VA3, Astrovirus VA4, Astrovirus MLB1, Human Astrovirus 1