Astrovirus

Astroviridae Family

The International Committee on the Taxonomy of Viruses (ICTV) currently recognizes two genera of astroviruses, Mamastrovirus (which infect mammals, including humans, cats, dogs, pigs, sheep, cattle, and deer) and Avastrovirus (which infect birds, including ducks, chickens, and turkeys). Immunologic studies have identified eight distinct serotypes of human astrovirus (HAstV), all of which appear to cause diarrheal illness.

Fig.1 Phylogenetic tree of representative members of the Astroviridae family. (Vu, 2017)

Astrovirus Structure

Astroviruses are a type of virus that causes gastroenteritis and belong to the Astroviridaefamily. Because the viral particles were found to display a star-like morphology by negative-staining transmission electron microscopy, astroviruses gained their name. Astroviruses are small, nonenveloped, icosahedral viruses with a positive-sense, single-stranded RNA genome of approximately 7 kb in size. The viral particle has a rippled, solid capsid shell of 33 nm in diameter that is decorated with 30 dimeric spikes extending 5 nm from the surface.

Fig.2 Astrovirus capsid structure model. (Dubois, 2013)

The Genome of HAstV

The genome is 6,700 to 7,000 nucleotides long and contains three open reading frames (ORFs). ORF1a and the downstream overlapping ORF1b encode two nonstructural polyproteins (nsp1a and nsp1ab), and ORF2 encodes the capsid protein (CP). The astrovirus CP is initially synthesized as VP90 (Fig.1). VP90 assembles in infected cells and undergoes C-terminal cleavages by caspases to generate VP70 for release from the cells as immature virus particles. Further trypsin cleavage to generate infectious particles usually results in three structural proteins, VP34, VP27, and VP25. Some astroviruses also contain an additional small open reading frame, ORFX, that encodes a viroporin.

Pathogenesis

Astrovirus pathogenesis has not been well studied in humans. Viral particles have been visualized in intestinal epithelial cells and epithelial cells located in the lower part of the villi, suggesting that the intestine is the site of replication. Rather than causing inflammation and cell death in the intestinal tract, astrovirus cause gastroenteritis by disrupting tight junctions and causing destruction of the intestinal epithelium, leading to the inhibition of usual absorption mechanism, allowing an influx of water, and resulting in diarrhea.

Epidemiology

HAstV infections occur worldwide. Globally, HAstV is estimated to cause 2 to 9% of cases of acute, nonbacterial diarrhea requiring hospitalization in children. Astroviruses tend to circulate more frequently during specific seasons and occur primarily in wintertime in temperate climates. Nevertheless, astroviruses are present year-round. The infection is transmitted from person to person through the fecal-oral route, even though food and water may act as vehicles for human enteric virus transmission. Astroviruses are one of the leading causes of gastroenteritis in young children, elderly people, and immunocompromised adults.

Symptoms

HAstV infections can range anywhere from asymptomatic to mild diarrhea and even fatal systemic disease. The clinical signs of HAstV infection are watery diarrhea of about 3 days, lasting up to 10 days episodes of non-blood-stained stools in 24 h, often associated with fever, headache, nausea, diarrhea, and abdominal pain. Astrovirus infection is less likely to cause vomiting and dehydration compared to other causes of viral gastroenteritis.

Prevention and Treatment

• Prevention

The prevention of HAstV infections is essentially based on the control of the transmission routes and control of disease at the host level. No vaccines have been developed for HAstVs.

• Treatment

Astrovirus infection is generally mild and self-limiting, rarely leading to severe dehydration, hospitalization, or death. There is no anti-viral treatment for astrovirus infection, but in vitro data suggest that interferon, ribavirin, favipiravir, and nitazoxanide have antiviral properties, depending on the viral strain that was tested.

Anti-Astrovirus Products and Services

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References

1. Vu, D.L.; et al. Epidemiology of classic and novel human astrovirus: gastroenteritis and beyond. Viruses, 2017, 9(2).
2. Dubois R.M.; et al. Crystal structure of the avian astrovirus capsid spike. Journal of Virology. 2013, 87(14):7853-7863.

All products and services are intended for Research Use Only, and NOT to be used in diagnostic or therapeutic procedures.