1、Gastrointestinal VirusesViral GastroenteritisnIt is thought that viruses are responsible for up to 3/4 of all infective diarrhoeas.nViral gastroenteritis is the second most common viral illness after upper respiratory tract infection.nIn developing countries,viral gastroenteritis is a major killer o
2、f infants who are undernourished.Rotaviruses are responsible for half a million deaths a year.nMany different types of viruses are found in the gut but only some are associated with gastroenteritis.Associated with gastroenteritisnRotavirusesnAdenoviruses 40 41nCaliciviruses嵌杯病毒nNorwalk like viruses
3、or SRSV(Small Round Structured Viruses)nAstrovirusesnSRV(Small Round Viruses)nCoronavirusesnTorovirusesFound in the gut,not normally associated with gastroenteritisnPolionCoxsackie AnCoxsackie BnEchonEnteroviruses 68-71nHepatitis AnHepatitis EnAdenoviruses 1-39nReovirusesFound in the gut as opportun
4、istic infectionnCMVnHSVnVZVnHIVGastrointestinal VirusesVirusGenomeTypical diseaseincubationDuration Rotaviruses:Group A,B,Cds-segmented RNA Major cause of diarrhea in children1-3 days24-56 h5-8 days3-7 daysCalicivirusesNorwalk agentsssRNAInfects adults and childrenEpidemic viral gastroenteritis1-3 d
5、ays18-24 h1-3 days12-48 hEAd 40,41Linear dsRNA diarrhea in children 7-8 days 8-12 d Astrovirus+ssRNAInfects mainly children and elderly1-4 days1-4 dGastrointestinal VirusesnInfants:Rotavirus A;Adenovirus 40,41;Coxsackie A24 virusnInfants,children,and adults Norwalk virus;Calicivirus嵌杯病毒;astrovirus;R
6、otavirus B;Reovirus.Human RotavirusImportant Characteristicsn70 nm round,double shelled,enclosing a genome of 11 segments of double stranded RNA.Groups of Rotaviruses nGroup A subtypes 1,2,3,4(main human pathogens)(Further 7 subtypes)also infect animals(monkey,calf,mouse)nGroup B Infects pigs and ra
7、tsFound to cause extensive outbreaks in China in past decade nGroup C Infects Pigs(Occasionally Man)nGroup D Infects birds nGroup E Infects pigs PathogenesisnEssentially an ingestion disease(faecal-oral route)nIncubation is short:1 to 3 daysnIllness:Sudden onset watery diarrhoea,with or without vomi
8、ting.May last up to 6 days(or longer if immunocompromised).The disease is self limiting.nComplications:Dehydration may result,this can be severe and life threatening in young children.PathogenesisnGroup A:Main pathogen of infantile diarrheanGroup B:Cause epidemic adult diarrheanGroup C:Cause human o
9、r animal sporadic diarrheaImmunity:sIgALab.DiagnosisnIEM,nCell culture,nPAGE of RNA segments,nPCRnLatex agglutination nELISA Treatmentntreatment of dehydration by oral and/or intravenous fluids and electrolytesPreventionnNon specific factors:improved hygiene,education,clean waterSpecific-Breast feed
10、ing helps to provide passive immunity in the newborn(from maternal antibodies),Vaccination is still experimental.Enteric AdenovirusesnNaked DNA viruses,75 nm in diameter.nFastidious enteric adenovirus types 40 and 41 are associated with gastroenteritis.nAssociated with cases of endemic gastroenterit
11、is,usually in young children and neonates.Can cause occasional outbreaks.nPossibly the second most common viral cause of gastroenteritis(7-15%of all endemic cases).nSimilar disease to rotavirusesnMost people have antibodies against enteric adenoviruses by the age of three.nDiagnosed by electron micr
12、oscopy or by the detection of adenovirus antigens in faeces by ELISA or other assays.AstrovirusesnSmall RNA viruses,named because of star-shaped surface morphology,28 nm in diameter.nAssociated with cases of endemic gastroenteritis,usually in young children and neonates.Can cause occasional outbreak
13、s.nR e s p o n s i b l e f o r u p t o 1 0%o f c a s e s o f gastroenteritis.nSimilar disease to rota and adenoviruses.nMost people have antibodies by the age of three.nDiagnosed by electron microscopy only,often very difficult because of small size.CalicivirusesnSmall RNA viruses,characteristic sur
14、face morphology consisting of hollows.particles 35 nm in diameter.nAssociated mainly with epidemic outbreaks of gastroenteritis,although occasionally responsible for endemic cases.nLike Norwalk type viruses,vomiting is the prominent feature of disease.nMajority of children have antibodies against ca
15、liciviruses by the age of three.nDiagnosed by electron microscopy only,often difficult to diagnose because of small size.Norwalk-like VirusesnSmall RNA viruses,with ragged surface,35 nm in diameter,now classified as caliciviruses.nAlways associated with epidemic outbreaks of gastroenteritis,adults m
16、ore commonly affected than children.nAssociated with consumption of shellfish and other contaminated foods.Aerosol spread possible as well as faecal-oral spread.nAlso named winter vomiting disease,with vomiting being the prominent symptom,diarrhoea usually mild.nAntibodies acquired later in life,in
17、the US,only 50%of adults are seropositive by the age of 50.nDiagnosis is made by electron microscopy and by PCR.Other Possible Diarrhoeal VirusesCoronavirusesnRNA viruses with a crown-like appearancenNot convincing associated with gastroenteritis at presentSmall Round VirusesnSmall virus-like partic
18、les with a smooth surface,22-28nm in diameternMay possibly be parvoviruses,enteroviruses,or cubic bacteriophagesnOccasionally seen in the faeces of endemic or epidemic cases of gastroenteritisGastrointestinal VirusesVirusGenomeTypical diseaseincubationDuration Rotaviruses:Group A,B,Cds-segmented RNA
19、 Major cause of diarrhea in children1-3 days24-56 h5-8 days3-7 daysCalicivirusesNorwalk agentsssRNAInfects adults and childrenEpidemic viral gastroenteritis1-3 days18-24 h1-3 days12-48 hEAd 40,41Linear dsRNA diarrhea in children 7-8 days 8-12 d Astrovirus+ssRNAInfects mainly children and elderly1-4 days1-4 d
