Astrovirus VA4 (AstV‑VA4) is a rarely detected genotype of human astrovirus in the VA clade within the family Astroviridae. It is a non‑enveloped, positive‑sense single‑stranded RNA virus with an icosahedral capsid that exhibits a star‑like pattern in electron micrographs. Phylogenetically VA4 is distinct from the eight classic human astrovirus serotypes as well as from other VA and MLB genotypes.
Explanation
Astroviruses are small (28‑30 nm) non‑enveloped viruses with a positive‑sense RNA genome of approximately 6.4–7.7 kilobases encoding non‑structural proteins and a capsid protein. VA4 shares this general architecture but represents a separate lineage in the VA clade. It was identified through unbiased sequencing approaches in stool samples from children during surveillance studies. Reports of VA4 are limited, and its geographic distribution and prevalence are poorly understood. The virus has been found in both symptomatic and asymptomatic individuals in low numbers. There is no evidence linking VA4 to outbreaks of gastroenteritis, and its role in human disease remains speculative. As with other astroviruses, transmission is presumed to occur by the fecal–oral route, and the virus is stable in the environment. Because it is genetically divergent from well‑known astrovirus serotypes, detection relies on broad‑range PCR assays and sequencing.
Observations so far
Only a handful of VA4 sequences have been reported in the literature. These detections came from stool specimens collected in different countries as part of studies of enteric viromes, and VA4 was not consistently associated with diarrhoea. The scarcity of data prevents any assessment of pathogenicity or epidemiology. Astrovirus VA4 is a little‑known human astrovirus genotype that appears to circulate at very low levels. Continued molecular surveillance will be necessary to determine its prevalence and any potential clinical significance. Related Terms: Astrovirus VA1, Astrovirus VA2, Astrovirus VA3, Astrovirus MLB1, Human Astrovirus 4