NORWALK VIRUSPresented 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

diarrheao "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, infantselderly

• Higher rate of transmissibility in populations in close contact

Norwalk Virus vs Rotavirus

Norwalk virus Rotavirus+ssRNA of Caliciviridae family,

non-envelopeddsRNA of Reoviridae family,

non-enveloped

All agesMostly in young infants, rarely

in adults

Nausea and vomiting Excess dehydration

Diarrhea Diarrhea + dry/ sticky mucosa present

Abdominal cramps Weight 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.

DiagnosisDDx: 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/>.