Article

Annual incidence, serotype distribution, and genetic diversity of human astrovirus isolates from hospitalized children in Melbourne, Australia.

Department of Gastroenterology, Royal Children's Hospital, Parkville, Victoria, Australia.
Journal of Clinical Microbiology (Impact Factor: 4.23). 08/1996; 34(7):1750-3.
Source: PubMed

ABSTRACT The incidence of astrovirus infection in children under 5 years of age hospitalized for acute gastroenteritis in Melbourne, Australia, during 1995 was determined. Astrovirus was detected in 16 fecal specimens by Northern (RNA) dot blot analysis of RNA isolated from feces with an astrovirus-specific cDNA probe. The incidence of astrovirus infection was determined as 4.2% (16 of 378 total samples) compared with rates of 63.2, 3.7, and 4.2% for rotavirus, adenovirus, and all bacterial pathogens, respectively. Astrovirus was detected during the winter season and mainly in infants between 6 and 12 months of age. Serotyping of samples was carried out by reverse transcriptase PCR and direct sequencing of a 348-bp region of the capsid protein gene. Type 1 strains predominated (11 of 13 typeable samples), although type 4 isolates were also detected. Astrovirus was retrospectively identified in 13 fecal samples collected from hospitalized infants between 1980 and 1985 and shown to contain small viruses by electron microscopy. Type 1 isolates were again the most common, although a type 5 strain was also found. Comparative sequence analysis indicated that type 1 astroviruses exhibited up to 7% sequence divergence over a 15-year period; however, all mutations were silent. The incidence of astrovirus reported here indicates that the virus is a significant cause of severe diarrhea in young children. The genetic analysis also provides important molecular epidemiological information relevant to the development of preventative therapies.

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    ABSTRACT: Astroviruses were first identified over 30 years ago and the virus was soon established as an important cause of gastroenteritis, particularly in young children. Human astrovirus disease was thought to result from infection by a limited number of serotypes. However, recent studies have indicated that the extent of genetic diversity is greater than previously assumed. In addition, the widespread occurrence among animals and reports of recombination and possible cross-species transmission suggest that astroviruses have zoonotic potential. Astroviruses are small (28–30 nm), non-enveloped viruses belonging to the family Astroviridae. The viral genome comprises a single-stranded RNA of positive sense. The genome length is between 6.8 and 7.9 kb and includes a 50 bp untranslated region (UTR), followed by three open reading frames, ORF1a, ORF1b, and ORF2, a 30 bp UTR and a poly-A tail 1 . Figure 1 shows the genome structure of a typical astrovirus. ORF1a/1b encodes the viral non-structural proteins (protease and RNA-dependent RNA polymerase) while ORF2, expressed from a subgenomic RNA, encodes the viral capsid protein. Symptoms of disease Human astrovirus infection results in a mild, self-limiting gastroenteritis, generally indistinguishable from other causes of viral gastroenteritis, which sometimes requires hospitalisation. Diarrhoea is the predominant clinical symptom; however, disease can be accompanied by fever, nausea and occasionally vomiting, headache and abdominal discomfort. Co-infections with other enteric pathogens, especially rotaviruses, are known. Most infections in adults are asymptomatic. In other mammalian species, infection results in diarrhoea and gastroenteritis, while infection in birds leads to extraintestinal diseases, including interstitial nephritis in young chicks and acute hepatitis in ducklings 2 . Epidemiology The first description of astrovirus came in 1975 after electron microscopic analysis of diarrhoeal stool samples from infants 3,4 . The unusual appearance of the virion particles (10% show a characteristic five-or six-pointed star pattern on their surface) indicated a previously unrecognised virus. Astroviruses have since been reported worldwide in samples from infants and young children with gastroenteritis. Soon after the first report in humans, astrovirus-like particles were observed in domesticated animals. There is now abundant evidence that astroviruses are widespread among domestic, synanthropic and wild animals, avian and mammalian species in terrestrial and aquatic environments 1 . The list of animal species from which astroviruses have been identified (chronologically) includes sheep, cattle, chickens, pigs, dogs, cats, deer, ducks, mice, turkeys, mink, guinea fowl, cheetahs, bats, sea lions, dolphins and rats. Reports of unusual astroviruses that have possibly arisen through recombination events indicate that co-infections within and between species are possible. By convention, the naming of astroviruses has been according to species of origin (for example, human astroviruses are referred to as HAstV). The family Astroviridae is divided into two genera: Mamastroviruses (MAstVs) which infect mammals and Avastroviruses (AAstVs) which are known to infect avian species. HAstV are classified into eight 'classic' serotypes (HAstV 1-8). In recent years, new highly divergent human astroviruses (MLB1, VA1, VA2 and VA3) have been described 5-9 , some of which are genetically related to rat astroviruses. However, a case-control study has questioned the role of one of these new viruses, MBL1, in human disease 10 .
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    ABSTRACT: Acute gastroenteritis (AGE) is a common illness affecting all age groups worldwide causing 2.2 million deaths annually. Viruses including rotaviruses, noroviruses, enteric adenoviruses and astroviruses are the major cause of AGE, with rotavirus causing the majority of severe illness. Advances in molecular techniques have led to the identification of many more viruses in faeces. Proving an association with AGE will require prospective controlled trials which so far are few in number. In 2004, acute gastroenteritis (AGE) was the fifth most common cause of death in the world in 2004 causing 2.2 million deaths. In low-income countries it ranked third, causing 1.8 million deaths while in children less than five it was ranked equal first with respiratory disease, causing 17% of all deaths in that age group 1 .
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    ABSTRACT: Human astroviruses (HAtVs) are positive-sense single-stranded RNA viruses that were discovered in 1975. Astroviruses infecting other species, particularly mammalian and avian, were identified and classified into the genera Mamastrovirus and Avastrovirus. Through next-generation sequencing, many new astroviruses infecting different species, including humans, have been described, and the Astroviridae family shows a high diversity and zoonotic potential. Three divergent groups of HAstVs are recognized: the classic (MAstV 1), HAstV-MLB (MAstV 6), and HAstV-VA/HMO (MAstV 8 and MAstV 9) groups. Classic HAstVs contain 8 serotypes and account for 2 to 9% of all acute nonbacterial gastroenteritis in children worldwide. Infections are usually self-limiting but can also spread systemically and cause severe infections in immunocompromised patients. The other groups have also been identified in children with gastroenteritis, but extraintestinal pathologies have been suggested for them as well. Classic HAstVs may be grown in cells, allowing the study of their cell cycle, which is similar to that of caliciviruses. The continuous emergence of new astroviruses with a potential zoonotic transmission highlights the need to gain insights on their biology in order to prevent future health threats. This review focuses on the basic virology, pathogenesis, host response, epidemiology, diagnostic assays, and prevention strategies for HAstVs.
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