FAMILY CALICIVIRIDAE:FAMILY CALICIVIRIDAE:NorovirusesNoroviruses

To Be Discussed:To Be Discussed:

Taxonomy, structure and genomeTaxonomy, structure and genome

Disease manifestations and clinical symptomsDisease manifestations and clinical symptoms

DiagnosisDiagnosis

TransmissionTransmission

Epidemiology and incidence Epidemiology and incidence

Environmental resistanceEnvironmental resistance

Prevention and ControlPrevention and Control

Noroviruses TaxonomyNoroviruses Taxonomy

Previously- Family CaliciviridaePreviously- Family Caliciviridae

Genus:Genus: 1. Norwalk-Like Viruses (NLVs)1. Norwalk-Like Viruses (NLVs)

2. Sapporo-Like Viruses (SLVs)2. Sapporo-Like Viruses (SLVs)

Recently- Genus NorovirusesRecently- Genus Noroviruses

(formerly Norwalk-Like Viruses)(formerly Norwalk-Like Viruses)

The Norovirus GenusThe Norovirus Genus

Norwalk VirusNorwalk Virus

Desert Storm VirusDesert Storm Virus

Southampton VirusSouthampton Virus

Snow Mountain AgentSnow Mountain Agent

Hawaii VirusHawaii Virus

Toronto VirusToronto Virus

Bristol VirusBristol Virus

Jena VirusJena Virus

Viral MorphologyViral Morphology

Non-enveloped, icosahedralNon-enveloped, icosahedral

27-40 nm27-40 nm

Single structural capsid protein, 60kDSingle structural capsid protein, 60kD

- 180 molecules, folds into 90 - 180 molecules, folds into 90 dimers dimers

Distinguishing characteristic:Distinguishing characteristic:

32-cupped shaped depressions on the 32-cupped shaped depressions on the axes of the icosahedronaxes of the icosahedron

Norovirus Structure by EM

www.pubmed.gov PMID: 13679618

GenomeGenome(+) ss RNA, 7900 nt in length(+) ss RNA, 7900 nt in length

3 Open Reading Frames:3 Open Reading Frames:

ORF1= non-structural proteins- RdRp ORF1= non-structural proteins- RdRp + helicase + helicase

ORF2= structural capsid proteinORF2= structural capsid protein

ORF3= small protein, function unknownORF3= small protein, function unknown

5’ 3’

ORF1 ORF2 ORF3

RdRp hel cap ?

GenomeGenome

www.pubmed.gov; PMID: 13679618

www.allthevirologyonthewww.com

RdRp StructureRdRp Structure

Crystal structure from www.pubmed.gov PMID: 12706072

Replication StrategyReplication StrategyReplication suggested- Typical of positive-sense ss RNA viruses, unconfirmedReplication suggested- Typical of positive-sense ss RNA viruses, unconfirmed

Wagner et al. Basic Virology. www.netlibrary.com

Replication of the GenomeReplication of the Genome

Wagner et al. Basic Virology. www.netlibrary.com

Disease ManifestationsDisease Manifestations

Infects small intestines and causes Infects small intestines and causes gastroenteritisgastroenteritis

Expansion of the villi at proximal small Expansion of the villi at proximal small intestine and shortening of the microvilli intestine and shortening of the microvilli

-epithelial cells remain intact-epithelial cells remain intact

Incubation period: 24-48 hoursIncubation period: 24-48 hours

Mistakenly termed- “stomach flu”Mistakenly termed- “stomach flu”

Path of InfectionPath of Infection

Wagner et al. Basic Virology. www.netlibrary.com

Clinical SymptomologyClinical SymptomologyNon-bloody diarrheaNon-bloody diarrhea NauseaNausea

VomitingVomiting Abdominal crampsAbdominal cramps

MalaiseMalaise MyalgiasMyalgias

HeadacheHeadache Low-grade feverLow-grade fever

Symptoms last 12-60 hours.Symptoms last 12-60 hours.

Children tend to suffer from vomiting, while Children tend to suffer from vomiting, while adults tend to suffer from diarrhea.adults tend to suffer from diarrhea.

TransmissionTransmissionFecal-Oral Fecal-Oral Typically in contaminated drinking waterTypically in contaminated drinking waterMany sources found : Many sources found :

poorly maintained municipal poorly maintained municipal suppliessupplies

wellswellsrecreational lakesrecreational lakesswimming poolsswimming poolscruise ship watercruise ship waterfood handled by infected person or food handled by infected person or washed with contaminated waterwashed with contaminated water

Prevalence of Sources of TransmissionPrevalence of Sources of Transmission

Epidemiology and IncidenceEpidemiology and Incidence

Found Worldwide.Found Worldwide.

Burden: - ca. 267,000,000 annual casesBurden: - ca. 267,000,000 annual cases

- 612,000 hospitalizations- 612,000 hospitalizations

- 3,000 deaths- 3,000 deaths

Highly contagious: fewer than 100 virus Highly contagious: fewer than 100 virus particles can cause infectionparticles can cause infection

2002- Cruise ship bound for Alaska-2002- Cruise ship bound for Alaska-

13% of 1266 on board were 13% of 1266 on board were affected; contaminated drinking affected; contaminated drinking waterwater

EpidemiologyEpidemiology

Frankenhauser et al. www.cdc.gov

Prevention and ControlPrevention and Control

Highly Stable in environment-Highly Stable in environment-

resistant to: resistant to:

freezingfreezing

heating to 60heating to 60ºCºC

disinfection w/ chlorinedisinfection w/ chlorine

acidic conditionsacidic conditions

vinegarvinegar

alcoholalcohol

high sugar high sugar concentrationconcentration

Prevention and ControlPrevention and ControlInfection produces IgG, IgA and IgM, but Infection produces IgG, IgA and IgM, but antibodies are not protective.antibodies are not protective.No lasting immunity or protection from No lasting immunity or protection from reinfection. Transient immunity- lasting 3-4 reinfection. Transient immunity- lasting 3-4 months.months.Vaccine not likely.Vaccine not likely.No current antiviral drugs, however complete No current antiviral drugs, however complete recovery is most common.recovery is most common.Prevent by hand-washing, good hygiene, proper Prevent by hand-washing, good hygiene, proper water management, preparation of food.water management, preparation of food.

Things to Remember for ExamThings to Remember for Exam

Defining structural characteristic(s).Defining structural characteristic(s).

Nucleic acid/ genome type.Nucleic acid/ genome type.

How many open reading frames and what How many open reading frames and what each one contains (general).each one contains (general).

Cell tropism and effects; hint- Does Cell tropism and effects; hint- Does Norwalk virus kill intestinal epithelial cells?Norwalk virus kill intestinal epithelial cells?

Infectious dose; environmental stabilityInfectious dose; environmental stability

Lasting immunity?; protective antibodies Lasting immunity?; protective antibodies produced?produced?

ReferencesReferences

Centers for Disease Control and Prevention. “Norwalk-Like Viruses:” Centers for Disease Control and Prevention. “Norwalk-Like Viruses:” Public health consequences and outbreak management. MMWR Public health consequences and outbreak management. MMWR 2001; 50 (No. RR-9): [inclusive page numbers]. www.cdc.gov 2001; 50 (No. RR-9): [inclusive page numbers]. www.cdc.gov

- MMWR, 2003, Outbreaks on Cruise ships.- MMWR, 2003, Outbreaks on Cruise ships.

www.pubmed.gov suggested articles, PMID: 13679618; 14499247; www.pubmed.gov suggested articles, PMID: 13679618; 14499247; 14557646; 14715308; 12791850; 1270607214557646; 14715308; 12791850; 12706072

Wagner, E.K.; Martinez, H. Wagner, E.K.; Martinez, H. Basic VirologyBasic Virology. Malden, MA. Blackwell . Malden, MA. Blackwell Science, 1999. www.netlibrary.com Science, 1999. www.netlibrary.com

Dorlands Online Medical Dictionary. www.dorlands.com Dorlands Online Medical Dictionary. www.dorlands.com