Transcript When to think Viral - Department of Microbiology

Norovirus: Nature’s Perfect
Puke’o’genic Pathogen
Todd F. Hatchette MD FRCPC
Director, Virology and Immunology
QEII HSC
November 27, 2008
Overview
• Case
• Outline features of Norovirus
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Epidemiology
Transmission
Clinical features
Infection control concerns
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
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
Caliciviridae
• New classification: four genera
1. Norovirus – Found in human, cows and pigs
• Most common cause of human illness
• Includes the “Norwalk-like” agent
2. Sapovirus – Found in Humans and pigs
• “Saporo-like” agents
3. Vesivirus:
• Animal viruses – feline
4. Lagovirus:
• Mainly in rabbits/hares. Rarely has been isolated in humans
The Many Faces of Norovirus
(Zeng et al., 2006 Virology 346:312-323)
Caliciviridae
• Genetic variation occurs by recombination
5’
2C
3C
3D
3’
AAAAAA
ORF 1
ORF 3
ORF 2
– Occurs at the junction of the NS cassette and capsid regions
– May permit
virus to escape
host immunity
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 300400 outbreaks each year
• High attack rate
History
• Zahorsky 1929 describes “winter vomiting
disease”
– Outbreaks of non-bacterial gastro (NBG)
• Gordon et al 1940’s
– 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
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
Winter Vomiting disease
Lopman et al., 2003 BMC Public Health
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
Not Just a Winter Disease
Frankhauser et al., 2002 JID 186:1-7)
Not Just a Winter Disease
Frankhauser et al., 2002 JID 186:1-7)
Norovirus
clinical 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
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
33:622-628)
– Diarrhea more common in adults
– Vomiting is more common in children
• Prospective community cohort study in the
Netherlands (Rockx et al., 2002 CID 35:246-253)
Rockx et al., 2002
Duration of Shedding
Correlates with age but not duration or severity of symptoms
Rockx et al., 2002
Duration of Shedding
• 71 cases of gastroenteritis, 71 children were positive for
NV by RT-PCR (Murata et al. 2007 Ped Infect Dis J 26:46-49)
• Healthy Pediatric patients can shed for up to 47 days
Shedding and Immunosuppresion
• Up to a year in pediatric cancer patients
(Ludwig et al., 2008 J Med Virol. 80:1461-1467)
(Siebenga et al., 2008 JID: 994-1001)
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 (> 50%)
• Absence of bacterial pathogens
• Symptoms vary patient to patient
Norovirus Transmission
• Transmission
– Fecal Oral
• Direct contact
• Contaminated
fingers/hands
• Aerosol
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
Outbreaks of Gastroenteritis Reported to CDC
Jan 1996–Nov 2000*
N=348
Settings
MMWR 2001 50 RR-9
Mode of transmission
Food as a source
• Calicivirus stable on food for up to 1 week
(Mattison et al., 2007 J Food Pro 170:500-503)
4oC
Room temp
Why are they so Infectious?
Characteristics that facilitate their spread during epidemics
• Low infectious dose
• Prolonged asymptomatic shedding
• Environmental stability
– Survives <10ppm Chlorine, freezing and
heating to 60 oC
• Strain diversity
– Multiple antigenic and genetic types
• Incomplete immunity
MMWR 2001 50 RR-9
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)
• The higher the dose the more likely people
developed illness
(Teunis et al., 2008 J Med Virol 1468-1476)
Norovirus Persistence on Surfaces
(Clay et al., 2006 AJIC 34:41-43)
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
Norovirus and the cruise ship
industry
• 3/5 outbreaks described in the
MMWR (2002:51(49) 11121115) had repeated outbreaks
on subsequent cruises after
disinfections in accordance with
CDC recommendations
– Required “aggressive cleaning
and sanitizing” before
outbreaks stopped
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 13:396-403)
RT-PCR performed
9 primer sets
Visualize PCR products
Sequencing
Compare with GenBank
Report
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. 12:279-287)
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
Norovirus and Human Resistance
Lindesmith et al., 2003 Nat Med 9:548-553
Tan and Jiang, 2007
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)
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 >65 yrs
(Harris et al., 2008 EID 14:1546-1552)
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
Are Noroviruses “Emerging”
(Widdowson et al., 2005 EID 11:735-737)
• >2500 foodborne outbreaks of norovirus 19951997
– <1% 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
The “other” Pandemic
• Genogroup II.4
– First identified in mid
1990’s
Laboratory Reports of Norovirus-Positive
Specimens in England and Wales, 1991 to 2006
• Responsible for significant
outbreaks in Nursing
homes in US and acute
care facilities in Europe
• Continues to evolve
Lopman et al., 2008 PLoS Med 187-189
How did to arise?
• Could new variants arise in chronically
infected patients?
Siebenga et al., JID 2008 198:994-1001
Siebenga et al., JID 2008 198:994-1001
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 5:269-289
Norovirus the “Gastric Flu”
Den Haag (2006)
Sakai (2004-2006)
Lindesmith et al., 2008
PLoS Med 5:269-289
Hunter (2004-2006)
Farmington Hills (2002-2004)
Grimsby cluster (1995-2002)
Camberwell (1987-1995)
Norovirus the “Gastric Flu”
• Genetic drift of H3
Influenza A from
1983-1994
Bush et al., 1999 Science 286:1921-1925
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
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 13:1184-1188)
• Genetic diversity can occur through recombination
Nature’s Perfect Puke’o’genic
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.