Astrovirus
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2008-05-28T18:03:18Z
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{{Taxobox
| name = Astrovirus
| image = Astrovirus 4.jpg
| image_width = 150px
| image_caption = [[Transmission electron microscopy|Electron micrograph]] of Astroviruses
| virus_group = iv
| familia = Astroviridae
| subdivision_ranks = Species
| subdivision =
'''Genus''': ''Mamastrovirus''
:''Bovine astrovirus''
:''Feline astrovirus''
:''Human astrovirus''
:''Ovine astrovirus''
:''Porcine astrovirus''
:''Mink astrovirus''
'''Genus''': ''Avastrovirus''
:''Chicken astrovirus''
:''Duck astrovirus''
:''Turkey astrovirus''}}
'''Astrovirus''' is a type of [[virus]] that infects [[mammals]] and [[birds]]. Astroviruses belong to the virus family ''Astroviridae''. They were first described in the year 1975 using [[electron microscopes]] during an outbreak of [[diarrhoea]].<ref name="pmid51251">{{cite journal
|author=Madeley CR, Cosgrove BP
|title=Letter: 28 nm particles in faeces in infantile gastroenteritis
|journal=Lancet
|volume=2
|issue=7932
|pages=451–2
|year=1975
|pmid=51251
|doi=
}}</ref> Astrovirus has a non-segmented, single stranded, positive sense [[RNA]] [[genome]] within a non-enveloped [[icosahedral]] [[capsid]].<ref name="pmid11444028">{{cite journal
|author=Matsui SM, Kiang D, Ginzton N, Chew T, Geigenmüller-Gnirke U
|title=Molecular biology of astroviruses: selected highlights
|journal=Novartis Found. Symp.
|volume=238
|issue=
|pages=219–33; discussion 233–6
|year=2001
|pmid=11444028
|doi=
}}</ref>
==Signs and symptoms of human disease==
Members of a relatively new virus family, the astroviridae, astroviruses are now recognised as a cause of [[gastroenteritis]] in children and adults. The main symptoms are [[diarrhoea]], followed by nausea, [[vomiting]], [[fever]], malaise and abdominal pain. Some research studies have shown that the duration of the symptoms are approximately three to four days.Astrovirus infection is not usually a severe situation and only in some rare cases leads to [[dehydration]]. Infected people do not need hospitalization because symptoms reduce by themselves, after a small period of time.<ref name="pmid2904454">{{cite journal
|author=Madeley CR
|title=Virus diarrhoea in hospital
|journal=J. Hosp. Infect.
|volume=12
|issue=3
|pages=145–9
|year=1988
|pmid=2904454
|doi=10.1016/0195-6701(88)90001-1
}}
</ref>
===Diagnosis===
[[Electron microscopy]], enzyme-immunoassay ([[ELISA]]), [[immunofluorescence]], and [[polymerase chain reaction]] have all been used. These detect virus particle, antigens or viral nucleic acid in the stools of infected people.<ref name="pmid16033504">{{cite journal
|author=Guix S, Bosch A, Pintó RM
|title=Human astrovirus diagnosis and typing: current and future prospects
|journal=Lett. Appl. Microbiol.
|volume=41
|issue=2
|pages=103–5
|year=2005
|pmid=16033504
|doi=10.1111/j.1472-765X.2005.01759.x
|url=http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0266-8254&date=2005&volume=41&issue=2&spage=103
}}</ref>
===Epidemiology===
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.<ref name="pmid10434464">{{cite journal
|author=
|title=Infectious diseases in England and Wales: January to March 1999
|journal=Commun. Dis. Rep. CDR Suppl.
|volume=9
|issue=4
|pages=S1–20
|year=1999
|pmid=10434464
|doi=
}}</ref> 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 [[United States|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.<ref name="pmid9015126">{{cite journal
|author=Glass RI, Noel J, Mitchell D, ''et al''
|title=The changing epidemiology of astrovirus-associated gastroenteritis: a review
|journal=Arch. Virol. Suppl.
|volume=12
|issue=
|pages=287–300
|year=1996
|pmid=9015126
|doi=
}}</ref>
Humans of all ages are susceptible to astrovirus infection but children, the elderly and those that are [[immunocompromised]] are most prone. The majority of children have acquired astrovirus [[antibodies]] by the age of 5 and looking at the pattern of disease, it suggests that antibodies provide protection through adult life, until the antibody titre begins to decline later in life.<ref name="pmid9455876">{{cite journal
|author=Koopmans MP, Bijen MH, Monroe SS, Vinjé J
|title=Age-stratified seroprevalence of neutralizing antibodies to astrovirus types 1 to 7 in humans in The Netherlands
|journal=Clin. Diagn. Lab. Immunol.
|volume=5
|issue=1
|pages=33–7
|year=1998
|pmid=9455876
|doi=
|url=http://cvi.asm.org/cgi/pmidlookup?view=long&pmid=9455876
}}</ref><ref name="pmid8385155">{{cite journal
|author=Midthun K, Greenberg HB, Kurtz JB, Gary GW, Lin FY, Kapikian AZ
|title=Characterization and seroepidemiology of a type 5 astrovirus associated with an outbreak of gastroenteritis in Marin County, California
|journal=J. Clin. Microbiol.
|volume=31
|issue=4
|pages=955–62
|year=1993
|pmid=8385155
|doi=
|url=http://jcm.asm.org/cgi/pmidlookup?view=long&pmid=8385155
}}</ref>
Astroviruses cause disease worldwide, and they are second only to [[rotavirus]]es as the cause of childhood diarrhoea. The occurrence of astrovirus infection varies depending on the season. In [[temperate]] climates infection is highest during winter months. This is in contrast to [[tropical]] regions where prevalence is highest during the rainy season. This seasonal distribution of infection in temperate climates is rather puzzling. But the seasonal distribution in tropical climates can be explained by the impact of the rain particularly on breakdown of [[sanitation]] in developing countries.<ref name="pmid9015126">{{cite journal
|author=Glass RI, Noel J, Mitchell D, ''et al''
|title=The changing epidemiology of astrovirus-associated gastroenteritis: a review
|journal=Arch. Virol. Suppl.
|volume=12
|issue=
|pages=287–300
|year=1996
|pmid=9015126
|doi=
}}</ref>
The main mode of Astrovirus transmission is by contaminated food and water. Young children in childcare backgrounds or adults in military barracks are most likely to develop the disease.
==Prevention==
There is no [[vaccine]] or anti-viral treatment against the Astrovirus infection but personal hygiene can reduce the incidence of the illness.
==Microbiology==
===Taxonomic structure===
The [[family (biology)|family]] ''Astroviridae'' contains two [[genus|genera]]: ''Mamastroviruses'' which infect mammals, and ''Avastroviruses'' which infect birds. Within each genus, there are [[species]] of astroviruses, each of which is named after the host in which they replicate. The astroviruses are further subclassified within each species into [[serovar|serotypes]].<ref name="pmid12029155">{{cite journal
|author=Lukashov VV, Goudsmit J
|title=Evolutionary relationships among Astroviridae
|journal=J. Gen. Virol.
|volume=83
|issue=Pt 6
|pages=1397–405
|year=2002
|pmid=12029155
|doi=
|url=http://vir.sgmjournals.org/cgi/pmidlookup?view=long&pmid=12029155
}}</ref>
===Virus structure===
Astroviruses have a star like appearance with 5 or 6 points and their name is derived from the Greek word “astron” meaning star. They are [[Viral envelope|non-enveloped]] [[RNA]]viruses with cubic [[capsid]]s, approximately 28-30nm in diameter.<ref name="pmid15802951">{{cite journal
|author=Krishna NK
|title=Identification of structural domains involved in astrovirus capsid biology
|journal=Viral Immunol.
|volume=18
|issue=1
|pages=17–26
|year=2005
|pmid=15802951
|doi=10.1089/vim.2005.18.17
}}</ref>
===Genome===
Astroviruses have a [[genome]] composed of a single strand of positive sense [[RNA]]. The single strand of RNA has a [[poly A]] tail at the [[3' end]], but no [[5' cap]]. With the exclusion of polyadenylation at the [[3' end]], the genome is between 6.8-7.9 kb long.
The genome is arranged into 3 [[open reading frame]]s ([[ORF]]s), with an overlap of approximately 70 nucleotides between ORF1a and ORF1b. The remaining ORF is known as ORF2.<ref name="pmid8021608">{{cite journal
|author=Willcocks MM, Brown TD, Madeley CR, Carter MJ
|title=The complete sequence of a human astrovirus
|journal=J. Gen. Virol.
|volume=75 ( Pt 7)
|issue=
|pages=1785–8
|year=1994
|pmid=8021608
|url=http://vir.sgmjournals.org/cgi/pmidlookup?view=long&pmid=8021608
}}</ref>
==References==
{{reflist|2}}
{{Viral diseases}}
{{Gastroenterology}}
[[Category:Viral diseases]]
[[Category:Viruses]]
[[Category:Gastroenterology]]
[[Category:Foodborne illnesses]]
[[Category:Infectious diseases]]
[[es:Astroviridae]]
[[fr:Astroviridae]]
[[ja:アストロウイルス科]]
[[pl:Astrowirusy]]
[[pt:Astrovirus]]
[[zh:星狀病毒科]]