viral gastroenteritis

Transcription

1 viral gastroenteritis

2 What causes viral gastroenteritis? Rotaviruses Caliciviruses Astroviruses SRV (Small Round Viruses) Toroviruses Adenoviruses 40, 41

3 Diarrhea Causing Agents in World

4 ROTAVIRUS

5 Family Reoviridae Genus Segments Host Vector Orthoreovirus 10 Mammals None Orbivirus 11 Mammals Mosquitoes, flies Rotavirus 11 Mammals None Coltivirus 12 Mammals Ticks Seadornavirus 12 Mammals Ticks Aquareovirus 11 Fish None Idnoreovirus 10 Mammals None Cypovirus 10 Insect None Fijivirus 10 Plant Planthopper Phytoreovirus 12 Plant Leafhopper Oryzavirus 10 Plant Planthopper Mycoreovirus 11 or 12 Fungi None?

6 REOVIRUS REO: respiratory enteric orphan, early recognition that the viruses caused respiratory and enteric infections incorrect belief they were not associated with disease, hence they were considered "orphan " viruses

7 ROTAVIRUS PROPERTIES Virus is stable in the environment (months) Relatively resistant to hand washing agents Susceptible to disinfection with 95% ethanol, Lysol, formalin

8 STRUCTURAL FEATURES OF ROTAVIRUS 60 80nm in size Non enveloped virus EM appearance of a wheel with radiating spokes Icosahedral symmetry Double capsid Double stranded (ds) RNA in 11 segments

9 Rotavirus structure

10 The rotavirus genome consists of 11 segments of doublestranded RNA, which code for 6 structural viral proteins, VP1, VP2, VP3, VP4, VP6 and VP7 and 6 non-structural proteins, NSP1-NSP6, where gene segment 11 encodes both NSP5 and 6. Genome is encompassed by an inner core consisting of VP2, VP1 and VP3 proteins. Intermediate layer or inner capsid is made of VP6 determining group and subgroup specificities. i i The outer capsid layer is composed of two proteins, VP7 and VP4 eliciting neutralizing antibody responses.

11 CLASSIFICATION Groups 7 Groups (A through G) and Within group A, four different subgroups (SG); SGI, SGII, SGI and II, and noni/nonii, have been distinguished i d on the basis of VP6 diversity, it among which h possibly SGI or SGII are the only humans strains Group A is the most common Group B (outbreaks in China) Group C (worldwide)

12 CLASSIFICATION Serotypes Serotypes based on viral capsid proteins inducing neutralizing Ab 15 G serotypes based on VP7 (G serotypes) differences 5 predominant strains in U.S. (G1-G4, G9) account for 90% of isolates Strain G1 accounts for 73% of infections 25 P serotypes based on VP4 (P serotypes) with P4/P8 predominance Common PG combinations are: P8G1, P8G2, P4G2, P8G4

13 Rotavirus gene function

14 Rotavirus Pathogenesis Entry through mouth Targeted host cells - mature enterocytes lining the tips of intestinal villi Intermediate/infective sub-viral particle (ISVP) produced through h proteolysis Enter host cell by endocytosis Replication in epithelium of small intestine Replication outside intestine and viremia uncommon Infection leads to isotonic diarrhea

15 CLINICAL FEATURES Incubation period thought to be <4 days Fever can be high grade (>102 F in 30%) Vomiting, nausea precede diarrhea Diarrhea

16 MECHANISM OF DIARRHEA Watery diarrhea due to net secretion of intestinal fluid and loss of absorptive surface Activation of the enteric nervous system Role of NSP4 peptide regions as an enterotoxin Dehydration is the main contributor to mortality Secondary malabsorption of lactose and fat, and chronic diarrhea are possible

17 EPIDEMIOLOGY Age children 4mo - 2 years Asymptomatic infections are common, especially in adults Nosocomial infections Outbreaks Severe e e Disease young, immunocompromised

18 Rotavirus Immunity Antibody against VP7 and VP4 partially protective First infection usually does not lead to permanent immunity Reinfection can occur at any age Subsequent infections generally less severe

19 Rotavirus detection and strain characterization Laboratory procedures for diagnosis of rotavirus include : electron microscopy (EM), passive latex agglutination assays (LA), electropherotyping using polyacylamide gel electrophoresis (PAGE), enzyme-linked immunosorbent assays (ELISA) reverse transcription-polymerase chain reaction (RT-PCR)

20 TREATMENT AND PREVENTION Treatment Supportive oral, IV rehydration Prevention Hand hygiene and disinfection of surfaces Vaccine

21 Calicivirus

22 HUMAN CALICIVIRUSES (HuCV) Family Caliciviridae Non-enveloped RNA viruses with ss [+] sense RNA nm in size Contains single capsid protein

23 CLASSIFICATION Caliciviruses can be divided into: Norwalk and "Norwalk-like" viruses (NLV) "Sapporo-like" viruses (SLV) Vesiviruses Lagoviruses

24 CLASSIFICATION NLV (Norovirus) Norwalk virus Hawaii virus Snow Mountain virus Montgomery county virus Taunton (England) SLV (Sapovirus) Sapporo virus Manchester virus Houston/86 London/92

25 Norwalk virus: Clinical Features 24 hour incubation period Vomiting prominent Headache, myalgia, fever Diarrhea 1-3 days, less severe than rotavirus Affects all ages Treatment symptomatic rehydration, antidiarrheals Complications rare immunocompromised

26 SPREAD Person-to-person fecal-oral spread (stool/ vomitus) Fecal contamination of food or water Fomites (stool/ vomitus)

27 EPIDEMIOLOGY Worldwide distribution >23 million cases/year in the U.S. ا( 50% <) Major cause of food-borne outbreaks of Most people have had infections by age 4 years (by sero-prevalence studies)

28 DIAGNOSIS diagnosed by electron microscopy only, often difficult to diagnose because of small size Specimen: stool, vomitus, food, environmental swabs (during outbreak investigations) RT-PCR in state public health hlabs. Serology for epidemiologic purposes

29 Astrovirus Particles

30 Classification of Astrovirus Genus Astrovirus Family Astroviridae Human serotypes: HuAstV 1-8

31 ASTROVIRUS structure Small ss RNA virus Non-enveloped 27-32nm in size Contain 3 structural proteins Genome has been sequenced

32 ASTROVIRUS li i l ASTROVIRUS Clinical Features Infants and children are most often affected Elderly l and immunecompromised i persons also Short incubation period 1-4 days Nausea, vomiting, abdominal cramping and watery diarrhea Constitutional symptoms-fever, malaise, headache

33 ASTROVIRUS id i l ASTROVIRUS Epidemiology Endemic worldwide Mainly in children <7 years of age Transmission- person-to-person [fecal-oral] Outbreaks due to fecal contamination of sea-food or water

34 ASTROVIRUS Diagnosis EM (virus shed in stool in great numbers) EIA RT-PCR

35 Toroviruses Family Coronaviridae Genus Torovirus Human and animal pathogen Pleomorphic, coated ss (+) RNA virus Watery diarrhea in 2 12 months old Diagnosis: EM

36 Adenovirus Particle

37 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 occasional 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 EM or by the detection of adenovirus antigens in faeces by ELISA or other assays.

38 Diagnosis of viral diseases

39 Gastrointestinal Viral Infections Culture: rotaviruses, enteric adenoviruses (especially, serotypes 40 and 41), noroviruses, sapoviruses, astroviruses, and possibly toroviruses that is not readily cultivable. Electron Microscopy: Negative staining with uranyl acetate or phosphotungstic acid can be performed directly on stool specimens. especially the noroviruses and sapoviruses, are better visualized using immune electron microscopy

40 Gastrointestinal Viral Infections Antigen Detection: Many commercial assays that use for rotavirus detection, and at least one commercial adenovirus assay is available. Antigen detection assays for astrovirus have been used in investigations Nucleic Acid Amplification: In rotaviruses antigen detection assays better than RT-PCR because of the adequate sensitivity and greater simplicity. RT-PCR has been shown to be more sensitive than EIA for detection of astroviruses. RT-PCR is the method of choice for detection of noroviruses.

41 Types of Cell Culture Primary cell cultures; derived ddirectly from the source animal. include primary monkey kidney cells and primary rabbit kidney cells. Diploid or semicontinuous cells; are capable of a limited number of passages before undergoing senescence. Include human fibroblast cell cultures such as MRC-5 and WI-38 cells. Continuous or transformed cell lines; are immortalized cells that can be passaged without limit. include HEp-2, HeLa, A549, and Madin-Darby canine kidney cells.

42 Electron Microscopy for the direct visualization of viral particles in specimen. Advantages include speed, lack of requirement for viral viability, and that many different kinds of viral particles can potentially be seen (nature of the particle). Disadvantages include the cost and complexity of maintaining itii an electron microscopy, the need dfor a skilled operator, and limited sensitivity related to the relatively high concentration of viral particles.

43 1. Direct Specimen Examination (EM) diagnostic g virology is the evaluation of stool specimens from patients with suspected viral gastroenteritis. rotaviruses, enteric strains of adenovirus, noroviruses, and astroviruses, are not readily cultivable. All be seen by negatively stained using phosphotungstic acid or uranyl acetate. Rotaviruses and adenoviruses are easily seen. Noroviruses and sapoviruses are better visualized using immune electron microscopy

44 2. Examination of Fixed Tissue (EM) 3. Examination of Infected Cell Cultures(EM) when h they cannot be identified d by other methods. Although identification to the species level is not possible, identification of a virus family based on morphology can provide a starting point for more detailed identification.

45 Electronmicrographs Adenovirus Rotavirus

46 Antigen Detection passive latex agglutination assays (LA), Enzyme linked immunabsorbant assay(elisa)

47 Enzyme linked immunabsorbant assay(elisa) Sample to be tested Enzyme -> colo virus Detecting an Capturing antibody

48 Molecular Methods RT PCR Methods based on the detection of viral genome are also commonly known as molecular methods. It is often said that molecular methods is the future direction of viral diagnosis, and it is certain that the role of molecular methods will increase rapidly in the near future

49 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 28 in diameter may ypossibly be parvoviruses, enteroviruses, or cubic bacteriophages occasionally seen in the faeces of endemic or epidemic cases of gastroenteritis t