FAMILY CALICIVIRIDAE: Noroviruses

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FAMILY CALICIVIRIDAENoroviruses

• Teresa Kunkel
• 4-16-04
• Honors Virology Presentation

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To Be Discussed

• Taxonomy, structure and genome
• Disease manifestations and clinical symptoms
• Diagnosis
• Transmission
• Epidemiology and incidence
• Environmental resistance
• Prevention and Control

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Noroviruses Taxonomy

• Previously- Family Caliciviridae
• Genus 1. Norwalk-Like Viruses (NLVs)
• 2. Sapporo-Like Viruses (SLVs)
• Recently- Genus Noroviruses
• (formerly Norwalk-Like Viruses)

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The Norovirus Genus

• Norwalk Virus
• Desert Storm Virus
• Southampton Virus
• Snow Mountain Agent
• Hawaii Virus
• Toronto Virus
• Bristol Virus
• Jena Virus

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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

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Norovirus Structure by EM
www.pubmed.gov PMID 13679618
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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
ORF2
ORF3
hel
cap
?
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3
RdRp
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Genome
www.allthevirologyonthewww.com
www.pubmed.gov PMID 13679618
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RdRp Structure
Crystal structure from www.pubmed.gov PMID
12706072
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Replication Strategy

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

Wagner et al. Basic Virology. www.netlibrary.com
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Replication of the Genome
Wagner et al. Basic Virology. www.netlibrary.com
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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

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Path of Infection
Wagner et al. Basic Virology. www.netlibrary.com
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Clinical Symptomology

• Non-bloody diarrhea Nausea
• Vomiting Abdominal cramps
• Malaise Myalgias
• Headache Low-grade fever
• Symptoms last 12-60 hours.
• Children tend to suffer from vomiting, while
  adults tend to suffer from diarrhea.

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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

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Prevalence of Sources of Transmission
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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 Alaska-
• 13 of 1266 on board were affected
  contaminated drinking water

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Epidemiology
Frankenhauser et al. www.cdc.gov
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Outbreaks of Gastroenteritis Associated with
Noroviruses on Cruise Ships --- United States,
2002 During January 1--December 2, 2002, CDC's
Vessel Sanitation Program (VSP), which conducts
surveillance for acute gastroenteritis (AGE) on
cruise ships with foreign itineraries sailing
into U.S. ports (1), received reports of 21
outbreaks of AGE on 17 cruise ships. Of the 21
outbreaks, nine were confirmed by laboratory
analysis of stool specimens from affected persons
to be associated with noroviruses, three were
attributable to bacterial agents, and nine were
of unknown etiology. Seven outbreaks were
reported in 2001, and of these, four were
confirmed to be associated with norovirus (CDC,
unpublished data, 2002). This report describes
five of the norovirus outbreaks that occurred
during July 1--December 2, 2002, on cruise ships.
Outbreaks Cruise Ship A. On July 18, cruise
ship A, owned by cruise line A, embarked 1,318
passengers and 564 crew members for a 7-day
cruise from Vancouver to Alaska. On July 19, five
passengers reported to the ship's infirmary with
symptoms of AGE (Figure 1). By July 25, a total
of 167 (13) passengers and nine (2) crew
members had reported illness. Among the 176
patients, the predominant symptoms were vomiting
(76) and diarrhea (73). Five of 10 stool
specimens from ill passengers were positive for
norovirus by reverse transcriptase polymerase
chain reaction (RT-PCR). On July 25, when
passengers disembarked, the ship was disinfected
in accordance with CDC recommendations, and the
same day, a new group of passengers embarked for
another 7-day cruise. During the cruise, 189
(14) of 1,336 passengers and 30 (5.3) of 571
crew members had AGE with diarrhea (91) and
vomiting (85) (Figure 1). An environmental
health inspection conducted by CDC revealed no
sanitary deficiencies. Cruise line A cancelled a
subsequent cruise and voluntarily took the ship
out of service for 1 week for aggressive cleaning
and sanitizing. No outbreaks were reported on
subsequent cruises. Cruise Ship B. On October 1,
cruise ship B, also owned by cruise line A,
embarked 1,281 passengers and 598 crew members
for a 21-day cruise from Washington to Florida.
By October 16, a total of 101 (8) passengers and
14 (2) crew members reported to the infirmary
with AGE symptoms. On October 18, CDC
investigators boarded the ship to conduct an
epidemiologic and environmental investigation. Of
972 surveyed passengers, 399 (41) met the case
definition for AGE. Investigators found no
association between illness and water, specific
meals served on the ship, or with offshore
excursions. Stool specimens from 12 of 13
patients tested positive for norovirus.
Characterization of the strain by sequence
analysis of RT-PCR products matched those from
cruise ship A. Despite implementation of control
measures that included disinfection of the vessel
and quarantine of ill passengers and crew
members, a total of 264 passengers and 41 crew
members reported illness on three subsequent
10-day cruises. Cruise line A voluntarily
withdrew cruise ship B from service for 10 days
for aggressive cleaning and sanitizing. No
outbreaks were reported on subsequent voyages.
Cruise Ship C. On September 28, cruise ship C,
owned by cruise line B, embarked 1,984 passengers
and 941 crew members for a 7-day round-trip
cruise from Florida to the Caribbean. Several
passengers had AGE within 24 hours of
embarkation, and by October 1, a total of 70 (4)
passengers and two (0.2) crew members reported
illness. On October 3, CDC investigators boarded
the ship to conduct an epidemiologic and
environmental investigation. Questionnaires
completed by 1,879 (95) passengers and 860 (91)
crew members identified 356 (19) passengers and
13 (1.5) crew members who met the AGE case
definition. The epidemiologic investigation
suggested a point source of infection, followed
by cases associated with person-to-person
transmission. The investigation identified an
association between illness among passengers and
lunch served at embarkation (odds ratio2.4 95
confidence interval1.1--5.2 p value0.02). Four
of 11 stool specimens from patients were positive
for norovirus by RT-PCR. Characterization of the
strain by sequence analysis of RT-PCR products
matched those from an outbreak on the same ship
that occurred 3 weeks previously but was not
identical to the outbreak strain on cruise ships
A and B. CDC recommended reinforcing sanitation
practices and excluding ill foodhandlers from the
work place. Cruise ship C continued service, and
no new cases were reported on subsequent cruises.
Reported by EH Cramer, MD, D Forney, Vessel
Sanitation Program AL Dannenberg, MD, Div of
Emergency and Environmental Health Svcs, National
Center for Environmental Health MA Widdowson,
VetMB, JS Bresee, MD, S Monroe, PhD, RS Beard, H
White, MS, S Bulens, MPH, Div of Viral and
Rickettsial Diseases E Mintz, MD, C Stover, MPH,
Div of Bacterial Diseases, National Center of
Infectious Diseases E Isakbaeva, MD, J Mullins,
DVM, J Wright, DVM, V Hsu, MD, W Chege, MD, J
Varma, MD, EIS officers, CDC.
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Prevention and Control

• Highly Stable in environment-
• resistant to
• freezing
• heating to 60ºC
• disinfection w/ chlorine
• acidic conditions
• vinegar
• alcohol
• high sugar concentration

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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.

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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?

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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