NORWALK VIRUS

Presented by:Andrea Riley

Sharon WidjajaJessica 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 similarityo 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 antigenso Genogroup I noroviruses preferentially

recognize blood group antigens A and O.o Genogroup II noroviruses preferentially

recognize blood group antigens A and B.

Transmission

• Body fluid of infected person:o Vomitus

aerosolization one single vomiting incident may

produce an estimated 30 million viral particles

o 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

• Fecal-oral route

• Contaminated food and water consumption

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 Rotavirus

+ssRNA of Caliciviridae family, non-enveloped

dsRNA of Reoviridae family, non-enveloped

All agesMostly in young infants, rarely

in adults

Nausea and vomitingExcess dehydration

DiarrheaDiarrhea + dry/ sticky mucosa

present

Abdominal crampsWeight loss

Norwalk Virus vs Rotavirus

Norwalk Virus RotavirusVirus shedding up to 3 weeks

post-recoveryVirus 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. Symptoms develops within 2

days of exposure

No vaccines 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

ReferencesBlacklow 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/803885-overview>.

"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/>.