Post on 15-Dec-2015
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/>.