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1、Gastrointestinal Viruses,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
2、 infants who are undernourished.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,RotavirusesAdenoviruses 40 41Caliciviruses嵌杯病毒Norwalk like viruses or S
3、RSV(Small Round Structured Viruses)AstrovirusesSRV(Small Round Viruses)CoronavirusesToroviruses,Found in the gut,not normally associated with gastroenteritis,PolioCoxsackie ACoxsackie BEchoEnteroviruses 68-71Hepatitis AHepatitis EAdenoviruses 1-39Reoviruses,Found in the gut as opportunistic infectio
4、n,CMVHSVVZVHIV,Gastrointestinal Viruses,Gastrointestinal Viruses,Infants:Rotavirus A;Adenovirus 40,41;Coxsackie A24 virusInfants,children,and adults Norwalk virus;Calicivirus嵌杯病毒;astrovirus;Rotavirus B;Reovirus.,Human Rotavirus,Important Characteristics,70 nm round,double shelled,enclosing a genome
5、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 ratsFound to cause extensive outbreaks in China in past decade Group C Infects Pigs(Occasionally Man)Group D I
6、nfects birds Group E Infects pigs,Pathogenesis,Essentially an ingestion disease(faecal-oral route)Incubation is short:1 to 3 daysIllness:Sudden onset watery diarrhoea,with or without vomiting.May last up to 6 days(or longer if immunocompromised).The disease is self limiting.Complications:Dehydration
7、 may result,this can be severe and life threatening in young children.,Pathogenesis,Group A:Main pathogen of infantile diarrheaGroup B:Cause epidemic adult diarrheaGroup C:Cause human or animal sporadic diarrhea,Immunity:sIgA,Lab.DiagnosisIEM,Cell culture,PAGE of RNA segments,PCRLatex agglutination
8、ELISA,Treatment,treatment of dehydration by oral and/or intravenous fluids and electrolytes,Prevention,Non specific factors:improved hygiene,education,clean waterSpecific-Breast feeding helps to provide passive immunity in the newborn(from maternal antibodies),Vaccination is still experimental.,Ente
9、ric 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 occasional outbreaks.Possibly the second most common viral cause of
10、 gastroenteritis(7-15%of all endemic cases).Similar disease to rotavirusesMost people have antibodies against enteric adenoviruses by the age of three.Diagnosed by electron microscopy or by the detection of adenovirus antigens in faeces by ELISA or other assays.,Astroviruses,Small RNA viruses,named
11、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 gastroenteritis.Similar disease to rota and adenoviruses.Most people have antibodies
12、 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 diameter.Associated mainly with epidemic outbreaks of gastroenteritis,although occasionall
13、y 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 microscopy only,often difficult to diagnose because of small size.,Norwalk-like Viruses,Small RN
14、A 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 consumption of shellfish and other contaminated foods.Aerosol spread possible as well as faecal-ora
15、l 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 age of 50.Diagnosis is made by electron microscopy and by PCR.,Other Possible Diarrhoeal Viruses,Coronavi
16、rusesRNA viruses with a crown-like appearanceNot convincing associated with gastroenteritis at presentSmall Round VirusesSmall virus-like particles with a smooth surface,22-28nm in diameterMay possibly be parvoviruses,enteroviruses,or cubic bacteriophagesOccasionally seen in the faeces of endemic or epidemic cases of gastroenteritis,Gastrointestinal Viruses,
