Norovirus: Nature

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Norovirus Natures Perfect Pukeogenic Pathogen

• Todd F. Hatchette MD FRCPC
• Director, Virology and Immunology
• QEII HSC
• November 27, 2008

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Overview

• Case
• Outline features of Norovirus
• Epidemiology
• Transmission
• Clinical features
• Infection control concerns

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Case

• Thursday 1230 AM index case awoken from sleep
  with projectile vomiting
• Distressed
• Multiple vomiting episodes overnight
• Relocated to more comfortable location
• By 800AM was fatigued but otherwise well

• Friday 1700 hrs
• Patient 2 feels light headed and fatigued
• Nausea and vomiting begin at 1745
• Associated with
• profuse watery diarrhea
• Fever
• Chills
• Vomiting resolves by 0300hrs
• Diarrhea resolves next day

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Caliciviridae

• Members of the Caliciviridae
• (Calyx Latin for cup or chalice).
• sense, single-stranded RNA genome.
• EM structured.
• Size 26-40 nm

• Had been referred to by names are derived from
  the geographic area they are discovered
• Small round-structured virus (SRSV)
• Now classified into genogroups

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Caliciviridae

• New classification four genera
• Norovirus Found in human, cows and pigs
• Most common cause of human illness
• Includes the Norwalk-like agent
• Sapovirus Found in Humans and pigs
• Saporo-like agents
• Vesivirus
• Animal viruses feline
• Lagovirus
• Mainly in rabbits/hares. Rarely has been
  isolated in humans

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The Many Faces of Norovirus
(Zeng et al., 2006 Virology 346312-323)
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Caliciviridae

• Genetic variation occurs by recombination

• Occurs at the junction of the NS cassette and
  capsid regions

• May permit virus to escape host immunity

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Norovirus - Epidemiology

• Most common cause of sporadic gastroenteritis
• 23 million infections each year in the US
• Causes up to 50 of all food borne outbreaks
• Accounts for 54 of Gastro in Hospitals in UK
• Cost 184 million (US) between 2002-2003
• Common cause of travelers diarrhea
• Since 2002 PHAC has had approximately 300-400
  outbreaks each year
• High attack rate

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History

• Zahorsky 1929 describes winter vomiting disease
• Outbreaks of non-bacterial gastro (NBG)
• Gordon et al 1940s
• Collected stool samples from institutional
  outbreak of NBG filtrate fed to volunteers
• Showed it could be serially passed in humans
• Could not isolate pathogen in eggs

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History

• Norwalk Ohio, 1968
• Outbreak of winter vomiting disease in an
  elementary school
• 50 of students and teachers were infected
• Etiology could not be identified but stools saved
  and filtrates used in subsequent human
  experimentation
• Kapikian et al., 1972
• Able to visualize SRGV in EM from volunteers
  infected with filtrate from Norwalk outbreak

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Winter Vomiting disease
Lopman et al., 2003 BMC Public Health
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Why could it be seasonal?

• Possibly related to virus stability
• Social behaviors that increase the likelihood of
  person-to-person transmission
• Winter pressures on healthcare

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Not Just a Winter Disease
Frankhauser et al., 2002 JID 1861-7)
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Not Just a Winter Disease
Frankhauser et al., 2002 JID 1861-7)
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Norovirusclinical presentation

• Incubation 12-48hrs
• Onset abrupt or gradual
• adults commonly presents as explosive projectile
  vomiting, diarrhoea or both but either can occur
  alone
• myalgias, malaise and occasionally headaches
• low grade fever in 50
• Illness lasts 12-60 hrs

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Clinical Presentation

• Retrospective sturdy looking at large food borne
  outbreak in children and staff at 30 day care
  centers in Sweden (Gotz et al., 2001 CID
  33622-628)
• Diarrhea more common in adults
• Vomiting is more common in children
• Prospective community cohort study in the
  Netherlands (Rockx et al., 2002 CID 35246-253)

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Rockx et al., 2002
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Duration of Shedding
Correlates with age but not duration or severity
of symptoms
Rockx et al., 2002
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Duration of Shedding

• 71 cases of gastroenteritis, 71 children were
  positive for NV by RT-PCR (Murata et al. 2007 Ped
  Infect Dis J 2646-49)

• Healthy Pediatric patients can shed for up to 47
  days

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Shedding and Immunosuppresion

• Up to a year in pediatric cancer patients (Ludwig
  et al., 2008 J Med Virol. 801461-1467)

(Siebenga et al., 2008 JID 994-1001)
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Norovirus Clinical Presentation

• Clinical criteria for recognizing Norovirus
  outbreaks (Kaplan et al., 1982 Turcios, et al.
  2006)
• (99 specific/68 sensitive)
• Short incubation period (24-48 hours)
• Short symptomatic illness (12-60 hrs)
• High frequency of vomiting (gt 50)
• Absence of bacterial pathogens
• Symptoms vary patient to patient

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Norovirus Transmission

• Transmission
• Fecal Oral
• Direct contact
• Contaminated fingers/hands
• Aerosol

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Norovirus - Transmission

• Transmission associated with
• Contaminated food
• 9.2/13.8 million cases of food related illness in
  US secondary to calicivirus
• Any food not served hot (56oC for 30 min before
  preparation) can be a source of infection.
• Person to person contact
• Oysters
• NV can bind to the carbohydrates in the gut of
  shellfish
• Sick crew members contaminated the oyster field
• Contaminated water
• Genome has been identified in bottled water
• Mode of transmission sometimes not clear

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Outbreaks of Gastroenteritis Reported to CDC Jan
1996Nov 2000N348
Mode of transmission
Settings
MMWR 2001 50 RR-9
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Food as a source

• Calicivirus stable on food for up to 1 week
  (Mattison et al., 2007 J Food Pro 170500-503)

Room temp
4oC
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Why are they so Infectious? Characteristics that
facilitate their spread during epidemics

• Low infectious dose
• Prolonged asymptomatic shedding
• Environmental stability
• Survives lt10ppm Chlorine, freezing and heating to
  60 oC
• Strain diversity
• Multiple antigenic and genetic types
• Incomplete immunity

MMWR 2001 50 RR-9
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How Infectious is it?

• Human challenge studies are limited because the
  starting dose is unknown
• Try to quantify by EM but many particles are in
  aggregates
• Estimated that 49 of people exposed to a single
  virus particle will get infected. (Teunis et al.,
  2008 J Med Virol 1468-1476)

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• The higher the dose the more likely people
  developed illness

(Teunis et al., 2008 J Med Virol 1468-1476)
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Norovirus Persistence on Surfaces
(Clay et al., 2006 AJIC 3441-43)
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Norovirus and the cruise ship industry - the
ship of stools
The Carnival of crap

• 2002 21 outbreaks of acute gastroenteritis on
  17 cruise ships reported to CDC
• 9 were laboratory confirmed cases of Norovirus
• 9 unknown
• 26 land-based outbreaks reported during the same
  time

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Norovirus and the cruise ship industry

• 3/5 outbreaks described in the MMWR (200251(49)
  1112-1115) had repeated outbreaks on subsequent
  cruises after disinfections in accordance with
  CDC recommendations
• Required aggressive cleaning and sanitizing
  before outbreaks stopped

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Caliciviridae diagnosis

• Diagnosis
• Culture not successful
• EM
• laborious and relatively insensitive (requiring
  106 to 107 particles/g or ml of feces).
• RT-PCR
• Which gene to target?
• Testing 5 specimens appears to be ideal (Fisman
  et al, 2008)

Recent 3D culture has some success (Straube et
al., 2007 EID 13396-403)
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Norovirus pathogenesis

• Pathogenesis is not clear
• Lesions in the small bowel
• Broadening and blunting of intestinal villa
• Transient malabsorption of sugars and fats
• Decreased activity in brush border enzymes

(Hutson et al., 2004 Trends in Microbiol.
12279-287)
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Norovirus

• Long term immunity is not consistent and usually
  short lived
• Immunity appears to be genotype specific
• Paradoxical association with antibody level
• Suggests genetic factors

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Norovirus and Human Resistance
Lindesmith et al., 2003 Nat Med 9548-553
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Tan and Jiang, 2007
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Norovirus and Mortality

• Illness is generally self limiting
• Elderly can succumb to complications of
  dehydration
• Recent US estimates
• 310/23 million die each year
• 553/1.4 million cases of Salmonella die each year
• Others estimate lower (0-3.7 deaths/year)

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Norovirus and Mortality

• Case fatality in UK - 7.5/10000 cases
• Recent modeling data suggests that from 2001-2006
  there were 228 deaths from norovirus related
  infections in England and Wales

• Represents 20 of deaths from infectious diseases
  in gt65 yrs

(Harris et al., 2008 EID 141546-1552)
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Prevention

• Good hand hygiene
• Alcohol based hand washes? - controversial
• Good food hygiene
• Discard stool vomit and clean with a bleach
  solution
• H2O2 products can also be used
• Patients to remain off work for 72 hrs after
  symptoms resolve

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Are Noroviruses Emerging(Widdowson et al.,
2005 EID 11735-737)

• gt2500 foodborne outbreaks of norovirus 1995-1997
• lt1 attributed to norovirus
• 68 were unknown etiology
• Today
• Responsible for up to 50 of food borne outbreaks
  in US
• Detected in 35 of persons with sporadic
  gastroenteritis

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The other Pandemic

• Genogroup II.4
• First identified in mid 1990s
• Responsible for significant outbreaks in Nursing
  homes in US and acute care facilities in Europe
• Continues to evolve

Laboratory Reports of Norovirus-Positive
Specimens in England and Wales, 1991 to 2006
Lopman et al., 2008 PLoS Med 187-189
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How did to arise?

• Could new variants arise in chronically infected
  patients?

Siebenga et al., JID 2008 198994-1001
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Siebenga et al., JID 2008 198994-1001
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Norovirus the Gastric Flu

• Evidence for genetic drift - the surface exposed
  carbohydrate binding domain is under heavy
  immunologic pressure
• Examined 176 full length GII.4 sequences from
  1987-2005
• Found 5 major clusters

Lindesmith et al., 2008 PLoS Med 5269-289
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Norovirus the Gastric Flu
Den Haag (2006)
Sakai (2004-2006)
Hunter (2004-2006)
Lindesmith et al., 2008 PLoS Med 5269-289
Farmington Hills (2002-2004)
Grimsby cluster (1995-2002)
Camberwell (1987-1995)
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Norovirus the Gastric Flu

• Genetic drift of H3 Influenza A from 1983-1994

Bush et al., 1999 Science 2861921-1925
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Norovirus the Gastric Flu

• Evidence of positive selection in AA in the P2
  protein (surface exposed region) but no single
  pattern was discernable
• VLPs containing representative samples had
  different binding affinities with different
  antigens

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Evidence for Zoontic transmission

• Noroviruses known to infect pigs, cattle, mice
• Cattle and pigs can be infected experimentally
  with human strains
• Human norovirus GII.4 was detected in fecal
  samples from cattle and swine and from retail
  meat samples (along with animal samples)
  (Mattison et al., 2007 EID 131184-1188)
• Genetic diversity can occur through recombination

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Natures Perfect Pukeogenic Pathogen

• The ultimate goal of a virus is not to kill its
  host but to find a new host to infect so that it
  can replicate its genetic material. What better
  way to do this than to induce explosive diarrhea
  and vomiting.