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FAMILY CALICIVIRIDAE:
Noroviruses
To Be Discussed:
Taxonomy, structure and genome
Disease manifestations and clinical symptoms
Diagnosis
Transmission
Epidemiology and incidence
Environmental resistance
Prevention and Control
Noroviruses Taxonomy
Previously- Family Caliciviridae
Genus: 1. Norwalk-Like Viruses (NLVs)
2. Sapporo-Like Viruses (SLVs)
Recently- Genus Noroviruses
(formerly Norwalk-Like Viruses)
The Norovirus Genus
Norwalk Virus
Desert Storm Virus
Southampton Virus
Snow Mountain Agent
Hawaii Virus
Toronto Virus
Bristol Virus
Jena Virus
Viral Morphology
Non-enveloped, icosahedral
27-40 nm
Single structural capsid protein, 60kD
- 180 molecules, folds into 90
dimers
Distinguishing characteristic:
32-cupped shaped depressions on the
axes of the icosahedron
Norovirus Structure by EM
www.pubmed.gov PMID: 13679618
Genome
(+) ss RNA, 7900 nt in length
3 Open Reading Frames:
ORF1= non-structural proteins- RdRp
+ helicase
ORF2= structural capsid protein
ORF3= small protein, function unknown
ORF1
5’
RdRp
hel
ORF2
cap
ORF3
?
3’
Genome
www.alltheviro
logyonthewww
.com
www.pub
med.gov;
PMID:
13679618
RdRp Structure
Crystal structure
from
www.pubmed.gov
PMID: 12706072
Replication Strategy
Replication suggested- Typical of positive-sense ss RNA
viruses, unconfirmed
Wagner et al. Basic Virology.
www.netlibrary.com
Replication of the Genome
Wagner et al. Basic Virology.
www.netlibrary.com
Disease Manifestations
Infects small intestines and causes
gastroenteritis
Expansion of the villi at proximal small
intestine and shortening of the microvilli
-epithelial cells remain intact
Incubation period: 24-48 hours
Mistakenly termed- “stomach flu”
Path of Infection
Wagner et al. Basic Virology. www.netlibrary.com
Clinical Symptomology
Non-bloody diarrhea
Vomiting
Malaise
Headache
Nausea
Abdominal cramps
Myalgias
Low-grade fever
Symptoms last 12-60 hours.
Children tend to suffer from vomiting, while
adults tend to suffer from diarrhea.
Transmission
Fecal-Oral
Typically in contaminated drinking water
Many sources found :
poorly maintained municipal supplies
wells
recreational lakes
swimming pools
cruise ship water
food handled by infected person or
washed with contaminated water
Prevalence of Sources of Transmission
Epidemiology and Incidence
Found Worldwide.
Burden: - ca. 267,000,000 annual cases
- 612,000 hospitalizations
- 3,000 deaths
Highly contagious: fewer than 100 virus
particles can cause infection
2002- Cruise ship bound for Alaska13% of 1266 on board were
affected; contaminated drinking
water
Epidemiology
Frankenhauser et al. www.cdc.gov
Prevention and Control
Highly Stable in environmentresistant to:
freezing
heating to 60ºC
disinfection w/ chlorine
acidic conditions
vinegar
alcohol
high sugar concentration
Prevention and Control
Infection produces IgG, IgA and IgM, but
antibodies are not protective.
No lasting immunity or protection from
reinfection. Transient immunity- lasting 3-4
months.
Vaccine not likely.
No current antiviral drugs, however complete
recovery is most common.
Prevent by hand-washing, good hygiene, proper
water management, preparation of food.
Things to Remember for Exam
Defining structural characteristic(s).
Nucleic acid/ genome type.
How many open reading frames and what
each one contains (general).
Cell tropism and effects; hint- Does
Norwalk virus kill intestinal epithelial cells?
Infectious dose; environmental stability
Lasting immunity?; protective antibodies
produced?
References
Centers for Disease Control and Prevention. “Norwalk-Like Viruses:”
Public health consequences and outbreak management. MMWR
2001; 50 (No. RR-9): [inclusive page numbers]. www.cdc.gov
- MMWR, 2003, Outbreaks on Cruise ships.
www.pubmed.gov suggested articles, PMID: 13679618; 14499247;
14557646; 14715308; 12791850; 12706072
Wagner, E.K.; Martinez, H. Basic Virology. Malden, MA. Blackwell
Science, 1999. www.netlibrary.com
Dorlands Online Medical Dictionary. www.dorlands.com