Astrovirus
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Astroviruses that infect humans have been poorly studied due to the fact that they do not grow in culture. Astroviruses belong to the family Astroviridae along with a virus known as mamastrovirus. They were first described in the year 1975 using electron microscopes during an outbreak of diarrhoea. Astrovirus has a non-segmented, single stranded, positive sense RNA genome within a non-enveloped icosahedral capsid.
Astroviruses
Members of a relatively new virus family, the astroviridae, astroviruses are now recognised as a major cause of gastroenteritis in children and adults. They are non-enveloped viruses displaying cubic symmetry, approximately 28-30nm in diameter. The genome consists of a positive sense single strand of RNA encoding a varying array of structural proteins.
A study of intestinal disease in the UK, published in 1999 determined incidence as 3.8/1000 patient years in the community (95%CI, range2.3-6.4), the fourth most common known cause of viral gastroenteritis. Studies in the USA have detected astroviruses in the stools of 2-9% of children presenting symptoms; illness is most frequent in children of less than two years, although outbreaks among adults and the elderly have been reported. Early studies carried out in Glasgow demonstrated that a significant proportion of babies excreting virus particles, 12%, did not exhibit gastrointestinal symptoms, and seroprevalence studies carried out in the US have shown that 90% of children have antibody to HastV-1 by age 9, suggesting that (largely asymptomatic) infection is common. There is, as with most viral causes of gastroenteritis, a peak of incidence in the winter.
Symptoms include diarrhoea, headache, malaise and nausea, vomiting being a less common complaint, and are usually milder than those experienced with rotavirus infection, and as a result dehydration is less severe. Incubation takes 3-4 days, and symptoms persist for less than 5 days in uncomplicated cases.
Diagnosis is achieved using electron microscopy; immune amplification is not necessarily required due to large numbers of virus particles in the stools. ELISAs, immunofluorescence, and nucleic acid based techniques have all been used.
Treatment may not be required, rehydration using ORS helps maintain electrolyte balance. There is potential for development of vaccination as it appears infection proffers some short-term protection against viruses of the same serotype.
References
Caul, E. O. 1996. Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part II. The epidemiological perspective. J. Clin. Pathol. 49:959-964
Caul, E. O. 1996. Viral gastroenteritis: small round structured viruses, caliciviruses and astroviruses. Part I. The clinical and diagnostic perspective. J. Clin. Pathol. 49:874-880 Treanor, J. J., R. Dolin. 2005. Astroviruses and picobirnaviruses. 2201-2203, in: Mandell, Douglas and Bennett’s Principles and practice of infectious diseases (6th Ed.). Mandell G. L., Bennett J. E., Dolin R. (Editors). Elsevier Churchill Livingstone.
Viral Gastroenteritis. 67-72, in: Notes on Medical Virology (11th Ed.) M. C. Timbury. 1997. Churchilll Livingstone.
Kapikan A. Z., R. M. Chanock. 1989. Viral Gastroenteritis. 293-340, in: Viral infections of humans (3rd Ed.) Evans A. S. (Ed.) Plenum Medical Book company
Wheeler J. G., D. Sethi, J. M. Cowden, P. G. Wall, L. C. Rodrigues, D. S. Tompkins, M. J. Hudson, P. J. Roederick. 1999. Study of infectious intestinal disease in England: rates in the community, presenting to general practice, and reported to national surveillance. Br. Med. J. 318:1046-1050
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