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NORWALK VIRUS Presented by: Andrea Riley Sharon Widjaja Jessica Bell Introduction • • • • • First discovered in diarrheal stool specimens from school children in Norwalk, Ohio in 1968 during an epidemic of gastroenteritis Renamed Norovirus in 2002 by the International Committee on Taxonomy of Viruses Family: Caliciviridae Genus: Norovirus Symptoms: acute gastroenteritis Classification • • • • • • Baltimore classification: Class IV (+) ssRNA Non-enveloped 40 different strains within the genus 5 genogroups based on sequence similarity o human pathogens in genogroups I, II and IV Tropism - Small intestines Structure • • • • 27-35 nm in diameter Icosahedral symmetry composed of 90 dimers of the capsid protein 3 ORFs - 1st encodes polyprotein - 2nd encodes capsid proteins - 3rd encodes other proteins of unknown fxns Pathogenesis • • • Entry - oral ingestion Multiplication - small intestine (can cause transient lesions of intestinal mucosa) o damage of microvilli (blunted villi with intact mucosa and epithelial) o damaged epithelial cells causes malabsorption and enzymatic disorder lead to diarrhea o "virus-mediated changes in gastric motility and delayed gastric emptying" leads to vomiting Exit - shed in feces (up to 3 weeks) Pathogenesis cont'd • • • Binds to histo-blood group antigens o HBGAs are complex carbohydrates on RBCs, mucosal epithelia, saliva, milk and other body fluids o Polymorphism of HGBAs are defined by their Lewis, secretor, and ABO types o Norovirus targets gastrointestinal epithelial cells o Three distinct antigens - A, B, and O P2 domain of viral capsid recognizes these antigens at their terminal furose Different strains of noroviruses are likely to recognize different antigens o Genogroup I noroviruses preferentially recognize blood group antigens A and O. o Genogroup II noroviruses preferentially recognize blood group antigens A and B. Transmission • • • Fecal-oral route Contaminated food and water consumption Body fluid of infected person: o o Vomitus aerosolization one single vomiting incident may produce an estimated 30 million viral particles Feces (found in stool up to 3 weeks after recovery from symptoms) • • at the peak of an enteric virus infection, more than 1011 virions per gram may be excreted in the stool Highly contagious - as few as 10 fomites can cause infection Non-enveloped viruses remain viable longer on surfaces than enveloped viruses Epidemiology • • • • • • Accounts for more than 96% of viral gastroenteritis cases in the U.S alone. Nearly 50% of all acute, infectious nonbacterial gastroenteritis cases in the United States Usually lasted for 24-72 hours. All ages Rare deaths o immunocompromised, infants elderly Higher rate of transmissibility in populations in close contact Norwalk Virus vs Rotavirus Norwalk virus +ssRNA of Caliciviridae family, nonenveloped All ages Nausea and vomiting Diarrhea Abdominal cramps Rotavirus dsRNA of Reoviridae family, nonenveloped Mostly in young infants, rarely in adults Excess dehydration Diarrhea + dry/ sticky mucosa present Weight loss Norwalk Virus vs Rotavirus Norwalk Virus Rotavirus Virus shedding up to 3 weeks postrecovery Virus shedding up to 10 days since onset of symptoms Rare deaths (immunocompromised, infants) Deaths due to dehydration Symptoms develops within 24-48 hrs from ingestion. No vaccines Symptoms develops within 2 days of exposure Vaccines available Case Study Several adults complained of serious diarrhea, nausea, vomiting, and a mild fever 2 days after visiting Le Cafe' Grease. The symptoms were too severe to result from food poisoning or a routine gastroenteritis, but lasted only 24 hours. Diagnosis DDx: staph aureus, campylobacter, shigella, salmonella, escherichia coli, clostridium difficile, enterovirus, norovirus Check for virus in stool samples and vomitus Antibodies detection in serum samples by immune electron microscope and immunoassay techniques Real-time PCR on stool or vomitus samples • • • Treatment and Medication • • • • • • Usually runs its course in 1-2 days Stay hydrated with water and electrolytes Avoid sugary beverages (worsen diarrhea) Intravenous fluids and electrolyte resuscitation if nausea is too severe. Antiperistaltic agents for patients with severe diarrhea, but not recommended for infectious diarrhea. Symptoms usually resolves by itself within 24- 48 hours. Prevention • • • • • • • No vaccine at this time, but active field of research! WASH HANDS! Especially after bathroom usaged Identification of contaminated sources Sanitization and disinfection of contaminated sites Strict hygiene monitoring of food handlers Water supplies should be protected from the risk of contamination from sewage Education References Blacklow NR. Norwalk Virus and Other Caliciviruses. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 65. Available from: http://www.ncbi.nlm.nih.gov/books/NBK8545/ Boone SA, Gerba CP. 2007. Significance of fomites in the spread of respiratory and enteric viral disease. Appl. Environ. Microbiol. 73: 1687–1696 Huang P, Farkas TM, Marionneau S, et al. Noroviruses bind to human ABO, Lewis, and secretor histo-blood group antigens: identification of 4 distinct strain-specific patterns. J Infect Dis 2003 Jul 1;188(1):19-31 Khan, Zartash Zafar, MD, Mark Martin Huycke, MD, Todd S. Wills, MD, and Michelle A. Jaworski, MD. "Norwalk Virus." Medscape.com. WebMD Health Professional Network, 11 Jan. 2012. Web. 18 Oct. 2012. <http://emedicine.medscape.com/article/224225-overview>. Nguyen, David D., Sally Henin Awad, and Brent R. King. "Rotavirus." Medscape.com. WebMD Health Professional Network, 2012. Web. 18 Oct. 2012. <http://emedicine.medscape.com/article/803885overview>. "Norovirus." Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 12 Apr. 2012. Web. 18 Oct. 2012. <http://www.cdc.gov/norovirus/about/index.html>. Prasad B. V., Rothnagel R, Jiang X, Estes M.K. (1994). Three-dimensional structure of baculovirus-expressed Norwalk virus capsids. J. Virol 68, 5117-5125. Website: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC236455/ "Viral Gastroenteritis." Viral Gastroenteritis. Ed. A.D.A.M. U.S. National Library of Medicine, 18 Nov. 0000. Web. 18 Oct. 2012. <http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001298/>.