Astrovirus
Encyclopedia
Astrovirus is a type of virus
that was first discovered in 1975 using electron microscopes following an outbreak of diarrhoea in humans. 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. Astrovirus has a non-segmented, single stranded, positive sense RNA
genome
within a non-enveloped
icosahedral capsid
. Human astroviruses have been shown in numerous studies to be an important cause of gastroenteritis in young children worldwide.
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 short time.
), immunofluorescence
, and polymerase chain reaction
have all been used for detecting virus particle, antigens or viral nucleic acid in the stools of infected people. A method using real-time RT-PCR, which can detect all human astrovirus genotypes, has been reported.
, range 2.3–6.4), 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 younger than 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.
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.
Astroviruses are associated with 5%–9% of cases of gastroenteritis in young children. 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.
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.
or anti-viral treatment against the Astrovirus infection but personal hygiene can reduce the incidence of the illness.
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.
There are at least three genotypes of bovine astroviruses. These appear to be related to the Capreolus capreolus astrovirus.
RNA
viruses with cubic capsid
s, approximately 28–35 nm in diameter.
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 frame
s (ORF
s), with an overlap of approximately 70 nucleotides between ORF1a and ORF1b. The remaining ORF is known as ORF2.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
that was first discovered in 1975 using electron microscopes following an outbreak of diarrhoea in humans. 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. Astrovirus has a non-segmented, single stranded, positive sense RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
within a non-enveloped
Viral envelope
Many viruses have viral envelopes covering their protein capsids. The envelopes typically are derived from portions of the host cell membranes , but include some viral glycoproteins. Functionally, viral envelopes are used to help viruses enter host cells...
icosahedral capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
. Human astroviruses have been shown in numerous studies to be an important cause of gastroenteritis in young children worldwide.
Signs and symptoms in humans
Members of a relatively new virus family, the astroviridae, astroviruses are now recognised as a cause of gastroenteritisGastroenteritis
Gastroenteritis is marked by severe inflammation of the gastrointestinal tract involving both the stomach and small intestine resulting in acute diarrhea and vomiting. It can be transferred by contact with contaminated food and water...
in children and adults. The main symptoms are diarrhoea, followed by nausea, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
, fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, 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
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
. Infected people do not need hospitalization because symptoms reduce by themselves, after a short time.
Diagnosis
Electron microscopy, enzyme-immunoassay (ELISAELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
), immunofluorescence
Immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...
, and polymerase chain reaction
Polymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
have all been used for detecting virus particle, antigens or viral nucleic acid in the stools of infected people. A method using real-time RT-PCR, which can detect all human astrovirus genotypes, has been reported.
Epidemiology
A study of intestinal disease in the UK, published in 1999, determined incidence as 3.8/1000 patient years in the community (95% CIConfidence interval
In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
, range 2.3–6.4), 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 younger than than two years, although outbreaks among adults and the elderly have been reported. Early studies carried out in Glasgow
Glasgow
Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...
demonstrated that a significant proportion of babies excreting virus particles, 12%, did not exhibit gastrointestinal symptoms; seroprevalence
Seroprevalence
Seroprevalence is the number of persons in a population who test positive for a specific disease based on serology specimens; often presented as a percent of the total specimens tested or as a proportion per 100,000 persons tested...
studies carried out in the US
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
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.
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.
Astroviruses are associated with 5%–9% of cases of gastroenteritis in young children. The occurrence of astrovirus infection varies depending on the season. In temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
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
Sanitation
Sanitation is the hygienic means of promoting health through prevention of human contact with the hazards of wastes. Hazards can be either physical, microbiological, biological or chemical agents of disease. Wastes that can cause health problems are human and animal feces, solid wastes, domestic...
in developing countries.
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 vaccineVaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
or anti-viral treatment against the Astrovirus infection but personal hygiene can reduce the incidence of the illness.
Taxonomic structure
The familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Astroviridae contains two genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
: Mamastroviruses which infect mammals and Avastroviruses which infect birds. In each genus, there are species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of astroviruses, each named after the host in which they replicate. The astroviruses are further subclassified within each species into serotypes.
There are at least three genotypes of bovine astroviruses. 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-envelopedViral envelope
Many viruses have viral envelopes covering their protein capsids. The envelopes typically are derived from portions of the host cell membranes , but include some viral glycoproteins. Functionally, viral envelopes are used to help viruses enter host cells...
RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
viruses with cubic capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
s, approximately 28–35 nm in diameter.
Genome
Astroviruses have a genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
composed of a single strand of positive sense RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
. The strand has a poly A tail at the 3' end, but no 5' cap
5' cap
The 5' cap is a specially altered nucleotide on the 5' end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes. The process of 5' capping is vital to creating mature messenger RNA, which is then able to undergo translation...
. 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 frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
s (ORF
ORF
ORF may refer to:* ORF , the Austrian public service broadcaster.* Open reading frame, a portion of the genome.* The IATA airport code for Norfolk International Airport in Norfolk, Virginia.* ORF format , Olympus raw image file format....
s), with an overlap of approximately 70 nucleotides between ORF1a and ORF1b. The remaining ORF is known as ORF2.