Astrovirus

Astrovirus
Electron micrograph of Astroviruses
Virus classification
Group: Group IV ((+)ssRNA)
Family: Astroviridae
Genus & Species

Genus: Avastrovirus

Avian nephritis virus
Chicken astrovirus
Duck astrovirus
Turkey astrovirus

Genus: Mamastrovirus

Bovine astrovirus
Capreolus capreolus astrovirus
Feline astrovirus
Human astrovirus
Ovine astrovirus
Mink astrovirus
Porcine astrovirus

Astrovirus is a type of virus that was first discovered in 1975 using electron microscopes following an outbreak of diarrhoea in humans.[1] In addition to humans, astroviruses have now been isolated from numerous mammalian animal species (and are classified as genus Mammoastrovirus) and from avian species such as ducks, chickens, and turkey poults (classified as genus Aviastrovirus). Astroviruses are 28–35 nm diameter, icosahedral viruses that have a characteristic five- or sixpointed star-like surface structure when viewed by electron microscopy. Along with the Picornaviridae and the Caliciviridae, the Astroviridae comprise a third family of nonenveloped viruses whose genome is composed of plus-sense, single-stranded RNA.[2] Astrovirus has a non-segmented, single stranded, positive sense RNA genome within a non-enveloped icosahedral capsid.[3] Human astroviruses have been shown in numerous studies to be an important cause of gastroenteritis in young children worldwide.[2]

Signs and symptoms in humans

Members of a relatively new virus family, the astroviridae, astroviruses are now recognised as a cause of gastroenteritis in children, whose immune systems are underdeveloped, and elderly adults, whose immune systems are generally somewhat comprised. Presence of viral particles in fecal matter and in epithelial intestinal cells indicate that the virus replicates in the gastrointestinal tract of humans.[4] The main symptoms are diarrhoea, followed by nausea, vomiting, fever, malaise and abdominal pain. Some research studies have shown that the incubation period of the disease is approximately three to four days. Astrovirus infection is not usually a severe situation and only in some rare cases leads to dehydration. The severity and variation in symptoms correlates with the region the case develops in. This could be due to climatic factors influencing the life cycle or transmission method for that particular strain of Astrovirus. Malnutrition and immunodeficiency tend to exasperate the condition, leading to more severe cases or secondary conditions that could require hospital care.[5] Otherwise, infected people do not need hospitalization because symptoms will reduce by themselves, after 2 to 4 days.[6]

Diagnosis

Electron microscopy, enzyme-immunoassay (ELISA), immunofluorescence, and polymerase chain reaction have all been used for detecting virus particle, antigens or viral nucleic acid in the stools of infected people.[7] A method using real-time RT-PCR, which can detect all human astrovirus genotypes, has been reported.[8]

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, range 2.3–6.4), the fourth most common known cause of viral gastroenteritis.[9] Studies in the USA have detected astroviruses in the stools of 2–9% of children presenting symptoms; illness is most frequent in children younger 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; 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.[10]

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.[11][12]

Astroviruses are associated with 5–9% of cases of gastroenteritis in young children.[13] 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.[10]

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

Inactivated vaccines are in use for certain strains of Chicken Astrovirus (CastV).

There are no anti-viral treatment against infections but personal hygiene can reduce the incidence of the illness.

Microbiology

Taxonomic structure

-Group: ssRNA(+)

[14] The family Astroviridae contains two genera: Mamastroviruses which infect mammals and Avastroviruses which infect birds. In each genus, there are species of astroviruses, each named after the host in which they replicate. The astroviruses are further subclassified within each species into serotypes.[15]

There are at least three genotypes of bovine astroviruses.[16] These appear to be related to the Capreolus capreolus astrovirus.

Virus structure

Astroviruses have a star-like appearance with five or six points. Their name is derived from the Greek word "astron" meaning star. They are non-enveloped RNA viruses with cubic capsids, approximately 28–35 nm in diameter.[17]

Genus Structure Symmetry Capsid Genomic Arrangement Genomic Segmentation
AvastrovirusIcosahedralT=3Non-EnvelopedLinearMonopartite
MamastrovirusIcosahedralT=3Non-EnvelopedLinearMonopartite

[18]

Life Cycle

Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment to host receptors, which mediates endocytosis. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription, using an unknown model of subgenomic RNA transcription is the method of transcription. Translation takes place by -1 ribosomal frameshifting. Vertebrates serve as the natural host. Transmission routes are fecal-oral.[18]

Genus Host Details Tissue Tropism Entry Details Release Details Replication Site Assembly Site Transmission
AvastrovirusBirdsEnterocytesCell receptor endocytosisBuddingCytoplasmCytoplasmOral-fecal
MamastrovirusHumans; mammalsEnterocytesCell receptor endocytosisBuddingCytoplasmCytoplasmOral-fecal

Genome

Astroviruses have a genome composed of a single strand of positive sense RNA. The strand 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 three open reading frames (ORFs), with an overlap of approximately 70 nucleotides between ORF1a and ORF1b. The remaining ORF is known as ORF2.[19] ORF2 encode the structural proteins, which are -at least- VP26, VP29 and VP32, the most antigenic and immunogenic of these being VP26. This protein is probably involved in the first steps of viral infection, being a key factor in the biological cycle of astroviruses.[20]

The mutation rate has been estimated to be 3.7×10−3 nucleotide substitutions per site per year with the synonymous changes rate of 2.8×10−3 nucleotide substitutions per site per year.[21]

Evolution

The Astroviridae capsid is related to those of the Tymoviridae.[22] The non-structural region is related to the Potyviridae. It appears that this group of viruses may have arise at some point in the past as a result of recombination event between two distinct viruses and that this even occurred at the junction of the structural and non structural coding regions.

Species infected

In addition to humans, goats, cattle, pigs, wild boar, sheep, roe deer, bats, sea lions, rats, and mice are known to be infected with these viruses.[23][24][25]

References

  1. ↑ Madeley CR, Cosgrove BP (1975). "Letter: 28 nm particles in faeces in infantile gastroenteritis". Lancet. 2 (7932): 451–2. doi:10.1016/S0140-6736(75)90858-2. PMID 51251.
  2. 1 2 Brown DW, Gunning KB, Henry DM, et al. (January 2008). "A DNA Oligonucleotide Microarray for Detecting Human Astrovirus Serotypes". Journal of Virological Methods. 147 (1): 86–92. doi:10.1016/j.jviromet.2007.07.028. PMC 2238180Freely accessible. PMID 17905448.
  3. ↑ Matsui SM, Kiang D, Ginzton N, Chew T, Geigenmüller-Gnirke U (2001). "Molecular biology of astroviruses: selected highlights". Novartis Found. Symp. Novartis Foundation Symposia. 238: 219–33; discussion 233–6. doi:10.1002/0470846534.ch13. ISBN 978-0-470-84653-7. PMID 11444028.
  4. ↑ "The Epidemiology of Astroviruses". web.stanford.edu. Retrieved 2016-10-15.
  5. ↑ "Astroviruses - Infectious Disease and Antimicrobial Agents". www.antimicrobe.org. Retrieved 2016-10-15.
  6. ↑ "Astroviridae". web.stanford.edu. Retrieved 2016-11-11.
  7. ↑ Guix S, Bosch A, Pintó RM (2005). "Human astrovirus diagnosis and typing: current and future prospects". Lett. Appl. Microbiol. 41 (2): 103–5. doi:10.1111/j.1472-765X.2005.01759.x. PMID 16033504.
  8. ↑ Royuela E, Negredo A, Sánchez-Fauquier A (April 2006). "Development of a one step real-time RT-PCR method for sensitive detection of human astrovirus". Journal of Virological Methods. 133 (1): 14–9. doi:10.1016/j.jviromet.2005.10.012. PMID 16321452.
  9. ↑ "Infectious diseases in England and Wales: January to March 1999". Commun. Dis. Rep. CDR Suppl. 9 (4): S1–20. 1999. PMID 10434464.
  10. 1 2 Glass RI, Noel J, Mitchell D, et al. (1996). "The changing epidemiology of astrovirus-associated gastroenteritis: a review". Arch. Virol. Suppl. 12: 287–300. PMID 9015126.
  11. ↑ Koopmans MP, Bijen MH, Monroe SS, Vinjé J (1998). "Age-Stratified Seroprevalence of Neutralizing Antibodies to Astrovirus Types 1 to 7 in Humans in The Netherlands". Clin. Diagn. Lab. Immunol. 5 (1): 33–7. PMC 121387Freely accessible. PMID 9455876.
  12. ↑ Midthun K, Greenberg HB, Kurtz JB, Gary GW, Lin FY, Kapikian AZ (1993). "Characterization and seroepidemiology of a type 5 astrovirus associated with an outbreak of gastroenteritis in Marin County, California". J. Clin. Microbiol. 31 (4): 955–62. PMC 263593Freely accessible. PMID 8385155.
  13. ↑ Monroe SS, Holmes JL, Belliot GM (2001). "Molecular epidemiology of human astroviruses". Novartis Foundation Symposium. Novartis Foundation Symposia. 238: 237–45; discussion 245–9. doi:10.1002/0470846534.ch14. ISBN 978-0-470-84653-7. PMID 11444029.
  14. ↑ ICTV. "Virus Taxonomy: 2014 Release". Retrieved 12 June 2015.
  15. ↑ Lukashov VV, Goudsmit J (2002). "Evolutionary relationships among Astroviridae". J. Gen. Virol. 83 (Pt 6): 1397–405. PMID 12029155.
  16. ↑ Tse H, Chan WM, Tsoi HW, Fan RY, Lau CC, Lau SK, Woo PC, Yuen KY. (2011) Re-discovery and genomic characterization of bovine astroviruses. J Gen Virol.
  17. ↑ Krishna NK (2005). "Identification of Structural Domains Involved in Astrovirus Capsid Biology". Viral Immunol. 18 (1): 17–26. doi:10.1089/vim.2005.18.17. PMC 1393289Freely accessible. PMID 15802951.
  18. 1 2 "Viral Zone". ExPASy. Retrieved 12 June 2015.
  19. ↑ Willcocks MM, Brown TD, Madeley CR, Carter MJ (1994). "The complete sequence of a human astrovirus". J. Gen. Virol. 75 (7): 1785–8. doi:10.1099/0022-1317-75-7-1785. PMID 8021608.
  20. ↑ Royuela E. (2010). "Molecular cloning, expression and first antigenic characterization of human astrovirus VP26 structural protein and a C-terminal deleted form.". Comp Immunol Microbiol Infect Dis. 33 (277): 1–14. doi:10.1016/j.cimid.2008.07.010. PMID 18790534.
  21. ↑ Babkin IV, Tikunov AY, Zhirakovskaia EV, Netesov SV, Tikunova NV (2012) High evolutionary rate of human astrovirus. Infect Genet Evol
  22. ↑ Kelly AG, Netzler NE, White PA (2016) Ancient recombination events and the origins of hepatitis E virus. BMC Evol Biol 16(1):210
  23. ↑ Virus taxonomy: classification and nomenclature of viruses: Ninth Report of the International Committee on Taxonomy of Viruses. (2012) Ed: King, A.M.Q., Adams, M.J., Carstens, E.B. and Lefkowitz, E.J. San Diego: Elsevier.
  24. ↑ Phan, TG; Kapusinszky, B; Wang, C; Rose, RK; Lipton, HL; et al. (2011). "The Fecal Viral Flora of Wild Rodents". PLoS Pathog. 7 (9): e1002218. doi:10.1371/journal.ppat.1002218. PMC 3164639Freely accessible. PMID 21909269.
  25. ↑ Ng, TFF; Kondov, NO; Hayashimoto, N; Uchida, R; Cha, Y; et al. (2013). "Identification of an Astrovirus Commonly Infecting Laboratory Mice in the US and Japan". PLoS ONE. 8 (6): e66937. doi:10.1371/journal.pone.0066937.

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