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1、Viral Gastroenteritis,It is thought that viruses are responsible for up to 3/4 of all infective diarrhoeas. Viral gastroenteritis is the second most common viral illness after upper respiratory tract infection. In developing countries, viral gastroenteritis is a major killer of infants who are under
2、nourished. Rotaviruses are responsible for half a million deaths a year. Many different types of viruses are found in the gut but only some are associated with gastroenteritis.,Associated with gastroenteritis,Rotaviruses Adenoviruses 40 41 Caliciviruses嵌杯病毒 Norwalk like viruses or SRSV (Small Round
3、Structured Viruses) Astroviruses SRV (Small Round Viruses) Coronaviruses Toroviruses,Found in the gut, not normally associated with gastroenteritis,Polio Coxsackie A Coxsackie B Echo Enteroviruses 68-71 Hepatitis A Hepatitis E Adenoviruses 1-39 Reoviruses,Found in the gut as opportunistic infection,
4、CMV HSV VZV HIV,Gastrointestinal Viruses,Gastrointestinal Viruses,Infants: Rotavirus A; Adenovirus 40,41; Coxsackie A24 virus Infants, children, and adults Norwalk virus; Calicivirus嵌杯病毒; astrovirus; Rotavirus B; Reovirus.,Human Rotavirus,Important Characteristics,70 nm round, double shelled, enclos
5、ing a genome of 11 segments of double stranded RNA.,Groups of Rotaviruses,Group A subtypes 1, 2, 3, 4 (main human pathogens) (Further 7 subtypes) also infect animals (monkey, calf, mouse) Group B Infects pigs and rats Found to cause extensive outbreaks in China in past decade Group C Infects Pigs (O
6、ccasionally Man) Group D Infects birds Group E Infects pigs,Pathogenesis,Essentially an ingestion disease (faecal-oral route) Incubation is short : 1 to 3 days Illness: Sudden onset watery diarrhoea, with or without vomiting. May last up to 6 days (or longer if immunocompromised). The disease is sel
7、f limiting. Complications: Dehydration may result, this can be severe and life threatening in young children.,Pathogenesis,Group A: Main pathogen of infantile diarrhea Group B : Cause epidemic adult diarrhea Group C: Cause human or animal sporadic diarrhea,Immunity:sIgA,Lab. Diagnosis IEM, Cell cult
8、ure, PAGE of RNA segments, PCR Latex agglutination ELISA,Treatment,treatment of dehydration by oral and/or intravenous fluids and electrolytes,Prevention,Non specific factors: improved hygiene, education, clean water Specific - Breast feeding helps to provide passive immunity in the newborn (from ma
9、ternal antibodies), Vaccination is still experimental.,Enteric Adenoviruses,Naked DNA viruses, 75 nm in diameter. Fastidious enteric adenovirus types 40 and 41 are associated with gastroenteritis. Associated with cases of endemic gastroenteritis, usually in young children and neonates. Can cause occ
10、asional outbreaks. Possibly the second most common viral cause of gastroenteritis (7-15% of all endemic cases). Similar disease to rotaviruses Most people have antibodies against enteric adenoviruses by the age of three. Diagnosed by electron microscopy or by the detection of adenovirus antigens in
11、faeces by ELISA or other assays.,Astroviruses,Small RNA viruses, named because of star-shaped surface morphology, 28 nm in diameter. Associated with cases of endemic gastroenteritis, usually in young children and neonates. Can cause occasional outbreaks. Responsible for up to 10% of cases of gastroe
12、nteritis. Similar disease to rota and adenoviruses. Most people have antibodies by the age of three. Diagnosed by electron microscopy only, often very difficult because of small size.,Caliciviruses,Small RNA viruses, characteristic surface morphology consisting of hollows. particles 35 nm in diamete
13、r. Associated mainly with epidemic outbreaks of gastroenteritis, although occasionally responsible for endemic cases. Like Norwalk type viruses, vomiting is the prominent feature of disease. Majority of children have antibodies against caliciviruses by the age of three. Diagnosed by electron microsc
14、opy only, often difficult to diagnose because of small size.,Norwalk-like Viruses,Small RNA viruses, with ragged surface, 35 nm in diameter, now classified as caliciviruses. Always associated with epidemic outbreaks of gastroenteritis, adults more commonly affected than children. Associated with con
15、sumption of shellfish and other contaminated foods. Aerosol spread possible as well as faecal-oral spread. Also named “winter vomiting disease“, with vomiting being the prominent symptom, diarrhoea usually mild. Antibodies acquired later in life, in the US, only 50% of adults are seropositive by the
16、 age of 50. Diagnosis is made by electron microscopy and by PCR.,Other Possible Diarrhoeal Viruses,Coronaviruses RNA viruses with a crown-like appearance Not convincing associated with gastroenteritis at present Small Round Viruses Small virus-like particles with a smooth surface, 22-28nm in diameter May possibly be parvoviruses, enteroviruses, or cubic bacteriophages Occasionally seen in the faeces of endemic or epidemic cases of gastroenteritis,Gastrointestinal Viruses,